ISSN:0003-2654    

DOI:10.1039/AN97398FX005

出版商:RSC    

年代:1973

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN97398BX007

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

iv THE ANALYST [February, 1973THE ANALYSTEDITORIAL ADVISORY BOARDChairman: H. J. Cluley (Wembley)*L. S. Bark (Solford)R. Belcher (Birmingham)L. J. Bellamy, C.B.E. (Waltham Abbey)L. S. Birks (U.S.A.)E. Bishop (Exeter)E. A. M. F. Dahmen (The Netherlands)A. C. Docherty (Billingham)0. Dyrssen (Sweden)*W. T. Elwell (Birminghom)*D. C. Garratt (London)*R. Goulden (Sittingbourne)*R. C. Chirnside (Wembley)1. Hoste (6elgium)D. N. Hume (U.S.A.)H. M. N. H. Irving (Leeds)A. G. Jones (Welwyn Garden City)M. T. Kelley (U.S.A.)*J. A. Hunter (Edinburgh)W. Kemula (Poland)*G. F. Kirkbright (London)G. W. C. Milner (Horwell)G. H. Morrison (U.S.A.)*G. Nickless (Bristol)*J. M. Ottaway (Glosgow)*G. E. Penketh (6illingham)S. A. Price (Tadworth)D. I.Rees (London)E. B. Sandell (U.S.A.)A. A. Smales, O.B.E. (Harwell)H. E. Stagg (Manchester)E. Stahl (Germany)A. Walsh (Australia)T. S. West (London)P. Zuman (U.S.A.)*A. Townshend (Birmingham)* Members of the Board serving on the Executive Committee.NOTICE TO SUBSCRIBERSSubscriptions for The Analyst, Analytical Abstracts and Proceedings should beThe Chemical Society, Publications Sales Ofice,Blackhorse Road, Letchworth, Herts.Rates for 1973(other than Members of the Society)sent to:(a) The Analyst, Analytical Abstracts, and Proceedings, with indexes . . . . €37.00index), and Proceedings . . . . . . . . . . . . . . f38.00index), and Proceedings . . . . . . . . . . . . . . f45.00(b) The Analyst, Analytical Abstracts printed on one side of the paper (without(c) The Analyst, Analytical Abstracts printed on one side of the paper (withThe Analyst and Analytical Abstracts without Proceedings-(e) The Analyst, and Analytical Abstracts printed on one side of the paper (without(d) The Analyst and Analytical Abstracts, with indexes .. . . . . . . €34.00index) . . . . . . . . . . . . . . . . . . €3500(f) The Analyst, and Analytical Abstracts printed on one side of the paper (withindex) . . . . . . . . . . . . . . . . . . f 42.00(Subscriptions are NOT accepted for The Analyst and/or for Proceedings alonevi SUMMARIES OF PAPERS I N THIS ISSUE [February, 1973Summaries of Papers in this IssueIonic Polymerisation as a Means of End-point Indication inNon-aqueous Thermometric TitrimetryPart I.The Determination of Organic BasesA method for the thermometric titration of organic bases in non-aq~ieoussolution, in which ionic polymerisation is used to indicate t h c b end-point,has been evaluated for a range of aliphatic and aromatic amincm, includingsubstituted and polyfunctional amines, hcterocyclic nitrogen compounds,amides and some basic sulphur and phosphorus compounds. I’ercliloricacid and boron trifluoride were used as titrants ant1 a-mcthylstyrcnc andisobutyl vinyl ether were the monomers used, rcspcctivc.ly, in conjunctionwith them.The precision of the method with titrants o f niolarities from 0 . 1 to 0.001is of the order of 1.5 per cent. when a simple manual procetlurc: involvingthe use of a thermometer to measure the tcinperature is atloptcd.Moreelaborate methods, in which the temperature is nicasurc~l witli ;L thermistorand recorded, give precisions better than 1 pcr cent.Sample sizes down to about 0.0001 rnequiv, e.g., about 1 0 pg o f iiiorplio-line, which corresponds to 10 p.p.m. of morplioline in tliv voliiincs o f s;Linpl(~solution titrated, can be determined with 0.001 M titran ts. (‘a1il)rationgraphs show that the volume of titrant and amount o f sample are linearlyrelated in the range 0 to 3 ml of titrant.It is suggested that comparison of the results obtainc(l w1ic.n ;L 1 ) ; ~ s ~ istitrated with the two titrants, a Brransted acid and a J,ewis acitl, c;~n I)(\ usctlt o investigate some of the properties of the base.E.J. GREENHOW and L. E. SPENCERDepartment of Chemistry, Chelsea College, University of London, Manrc.;;L Road,J ,ondon, S,M7.3.Analyst, 1973, 98, 81-89.Ionic Polymerisation as a Means of End-point Indication inNon-aqueous Thermometric TitrimetryPart 11. The Determination of Organic AcidsA method for the thermometric titration of organic acids in non-aqueoussolution, involving the ionic polymerisation of acrylonitrile to indicate tlicend-point, has been evaluated for a range of mono- and polyacidic compounds,including phenols, triazine derivatives and tannic acid. In addition toacrylonitrile, methyl acrylate and dimethyl itaconate can be used as monomersfor the end-point indication. A number of titrant - catalysts have beenexamined, including tetra-n-butylammoniuni hydroxide, n-butyllithiuni andpotassium hydroxide.The precision of the method ranges from about 0.5 pcr ccnt.with 0.1 Mtitrant, to 2.7 per cent., with 0.001 M titrant, by using the manual andsemi-automatic methods described in Part I.Sample sizes down to about 0.0001 mequiv, e.g., about 10 p g of benzoicacid, which corresponds to 100 p.p.m. of benzoic acid in the volumes ofsample solution titrated, can be determined with 0.001 M titrant. Calibrationgraphs show the volume of titrant and mass of saniple to be linearly or almostlinearly related in the range 0 to 2 ml of titrant.Comparison of the titration values obtained by using thc acetone methodand ionic polymerisation with potassium hydroxide and tetra-n-butylam-monium hydroxide solutions as titrants enables one to differentiate betwccnacidic groups of different ionic strengths in the 10 to 12 pK, region.E.J. GREENHOW and L. E. SPENCERDepartment of Chemistry, Chelsea College, IJnivcrsity of I,ontlon, Mmirca I<oatl,London, S.W.3.Analyst, 1973, 98, 90-07February, 19731 SUMMARIES OF PAPERS I N THIS ISSUEIonic Polymerisation as a Means of End-point Indication inNon-aqueous Thermometric TitrimetryPart 111. The Determination of Alkaloids and Alkaloidal SaltsStrychnine, nicotine, atropine, quinine, papaverine, caffeine and tlieo-phylline have been determined in amounts down to 0.0001 mequiv, e.g.,33 pg of strychnine and 8.5 pg of nicotine, by catalytic thermometric titration.The hydrochlorides of quinine and ephedrine, ephedrine sulphate, codeinephosphate and atropine methonitrate have been determined by direct titra-tion by using the same technique.Addition of mercury(I1) acetate wasnot necessary in the titration of the hydrochlorides.Titrations were carried out in non-aqueous solution with 0.1, 0.01 and0.00 1 M perchloric acid, with the ionic polymerisation of a-methylstyreneto indicate the end-point. Depending on sample size and the procedureadopted, each determination can be carried out in 2 to 5 minutes by usinga manual method, with a thermometer for temperature measurement, ora simple automatic apparatus.The method would appear to be suitable for the determination o falkaloids and related basic compounds that have been extracted from crudedrugs, formulations or natural materials with non-basic organic solvents.For most of the determinations it is not necessary to dry wet chloroformextracts before titration.viiE.J. GREENHOW and L. E. SPENCERDepartment of Cliemistry, Chelsea College, IJnivcrsity of Idondon, Manresa Road,London, S.W.3.Analyst, 1973, 98, 98 - 102.Determination of Nitro and Nitroso Compounds by ThermometricTitrimetrySome nitro and nitroso compounds have been determined by reductionwith a known and excess amount of titanium(II1) chloride solution andsubsequent thermometric titration of the excess of the titanium(II1) withan iron(II1) solution.The accuracy is & 1 per cent. for 0.4 m equiv of sample and the timetaken for a single titration is less than 2 minutes. The over-all time takenfor a single determination is about 20 minutes.L. S. BARK and P. BATEDepartment of Chemistry and Applied Chemistry, University of Salford, Salford,Lancashire, M5 4WTAnalyst, 1973, 98, 103-106.Thin-layer Chromatography of Simple Urea - Formaldehyde -Methanol Reaction ProductsPart I. Qualitative AspectsMethods are described for the preparation of addition and condensationproducts of urea and formaldehyde of low relative molecular mass and theirmethyl esters. The stability of these compounds both as solids and in solutionis discussed. Conditions are described that enable most compounds to beseparated adequately by thin-layer chromatography without decompositionor other reaction occurring on the plate. The implications of the coloursgiven by the compounds on a chromatographic plate and the effect of sub-stituents on the RBl value are discussed.P. R. LUDLAMThe Borden Chemical Company (U. K.) Limited, North Haddeslcy, Southampton,SO5 9213.~n.alqJ.cf 1972 QR 1n7-11~

ISSN:0003-2654    

DOI:10.1039/AN97398FP013

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

x THE ANALYST [February, 1973IIANALYTICAL SCIENCESMONOGRAPHSA New SeriesBadge of The Society for Analytical ChemistryThe Society for Analytical Chemistry’s primary objects are toencourage, assist and extend the knowledge and study of analyticalchemistry. To this end the publication of journals, reports and bookshas always been recognised as an essential function. This month theSAC publishes the f i r s t in a new series of Monographs -H igh-Precision Titrimetryby C. Woodward and H. N. RedmanImperial Chemical Industries Limited (Agricultural Division)BRIEF CONTENTS:IntroductionVisual Titrations, with sections on Apparatus, Standard Substances and their preparationInstrumental Methods, with sections on Photometric Titrations, Electrometric Titrationsand assay, and Standard Solutions.and Miscellaneous Techniques.References t o the literature of high-precision titrimetry.Pp.viii +63Price f2-50Members of The Chemical Society (which includes members of the SAC) maybuy a personal copy a t the special price of f2.00 provided they state the fact ofsuch membership on their order and send with it a remittance for the correctamount made out t o “Society for Analytical Chemistry.”This Monograph i s now available from-THE SOCIETY FOR ANALYTICAL CHEMISTRY(Book Depart men t)9/10 SAVILE Row, LONDON WIX IAFebruary, 19731 THE ANALYST xiNew Chemistry Titles from The Butterworth GroupCoordination ChemistryExperimental Methods Kalrpzhn BurgThe object of this book is to provide a convenient and authoritative gnido to tho soloctionof suitable experimental methods for solving specific problems in coordination chemistq.The theoretical principles of the various methods are discussed only so far as is necessaryfor an appreciation of their scope; their application in coordination chemistry is verythoroughly covered, with numerous carefully selected examples from tho recent litoraturo.1973 370 p p 0 408 70205 2 $5.00Laboratory Techniques in Food AnalysisD.PearsonThis volume provides an introduction to the basic laboratory t,c~chniqii~s of food analysisfor students and technicians. A suitable course book for stixtlcnts, itJ is also a valuahlorofercnce for bench workers in industry or public health contml. 1 tJ is o m of a sorios ofbooks on laboratory techniques.1973 328 p p illustrated 0 408 70424 1 g6.50IUPAC. Analytical Chemistry - 3(Brasov, 1971) Edited by P.Gh. ZugravescuThe book includes nine of the Plenary Lectures presented a t the Third National Con-ference on Analytical Chemistry held in Brasov, 22-26 September, 1971. Thoso papersdealt with Electrochemical Analysis, Spectrometric Analysis, Radiochomical Analyvis,Chromatography and Organic Analysis. It will be of intorost to postgratluato~ inchemistry, to researchers and a must for university librarics.I972 152 p p illustrated 0 408 70389 X $4.30 or $12.90IUPAC. Chemistry of Natural Products - VIII(New Delhi, 1972) Edited by T. R. GovindachariThese are the plenary lectures presented a t the Eighth International Symposium on thoChomistry of Natural Products held in New Delhi, India in February 1972.1973 184 p p illustrated 0 408 70437 3 €5.25 or $15.75IUPAC.Dissociation Constants of OrganicBase in Aqueous SolutionSupplement 1972 D. D. PerrinDesigned to be used in conjunction with the original table, which coverod tho literatureup to the end of 1961. The range of this table is more extensive than that of the original,notably because of the inclusion of Russian journals.1972 1160 p p 0 408 70408 X $22.50 or $67.50I UPAC publications are available in the USA and Canada from Crane, Russak & Co.Inc., 52 Vanderbilt Avenue, New Yo&, N Y 10017Available through any bookseller, or from the publisher.The Butterworth Group88 Kingsway, London WC2B 6ABShowroom and trade counter: 4-5 Bell Yard, WCxii SUMMARIES OF PAPERS IN THIS ISSUEThin-layer Chromatography of Simple Urea - Formaldehyde -Methanol Reaction ProductsPart 11.Quantitative AspectsA thin-layer chromatographic method for the determination o f urea,monomethylolurea and dimethylolurea in urea - formaldehyde resins isdescribed. The resin is treated with methanolic boron trifluoridc, wherebythe methylol compounds are quantitatively converted into their respectivemethyl ethers, Subsequent application of chromatography on silica gel platesthat have been previously treated with ammonia vapour in order to preventreaction of the urea derivatives results in the effective separation of thecomponents of low relative molecular mass, thus allowing their concentrationsto be determined.Examples are given illustrating the change in concen-tration of urea derivatives of low relative molecular mass with time in urea -formaldehyde formulations.P. R. LUDLAMThe Borden Chemical Company (U.K.) Limited, North Saddesley, Southampton,SO5 9ZB.Analyst, 1973, 98, 116-121.LFebruary, 1073A Gas-chromatographic Method for the Determination ofLow Concentrations of Acrylic Acid in Mixtures ofC, to C, Fatty Acids in Biological MaterialsThe presence of acrylic acid in mixtures of short-chain (C, to C,) fattyacids can be determined by gas chromatography by using a compositc columntechnique. By varying the proportions of the total column length occupiedby non-polar and polar liquid phases, the acrylic acid peak could be “moved”to a predetermined position on the chromatogram and complete separationfrom the other acids could be achieved.Suitable placing of the peak enabledthe concentration of acrylic acid to be accurately and quickly determined.R. C. NOBLE and J. W. CZERKAWSKIHannah Research Institute, Ayr, Scotland, KA6 5HL.Analyst, 1973, 98, 122-126.Automatic Logging and Processing of AutoAnalyzer Peaks withan Off-line, Time-sharing ComputerA complete data acquisition and processing system for use with TechniconAutoAnalyzers is described. The system involves the use of a Solartron Data-logger and a teleprinter terminal connected to the Honeywell G265 Time-Sharing Computer Service by a Post Office telephone line.AutoAnalyzer recorders are fitted with re-transmitting slide-wires toproduce voltages that are proportional to peak height. Laboratory-builtcircuits detect the occurrence of peaks and generate digitise-command signalsto the logging system.Peak-height voltages are output to a tape punchand a printer. A manual-entry unit enables coding data to be punched a t thebeginning of each tape.Ten AutoAnalyzer channels can be monitored simultaneously. Thechannel of origin of each value is identified by a number that precedeseach peak voltage.The computer is used to process the raw data generated by the Auto-Analyzers and datalogger. The limited area of core store available to eachcomputer user necessitates the use of several programs, which are calledsequentially into the core store, to process the data.The programs werewritten in the BASIC language by members of the authors’ Department.J. D. CAISEY and B. D. RIORDANToxicology Department, Glaxo Research Ltd., Fulmer, Buckingharnshire.Analyst, 1973, 98, 126-132February, 19731 THE ANALYST xiiiANNUAL REPORTSONANALYTICAL ATOMICSPECTROSCOPYVolume 1, 1 9 1THIS comprehensive and critical reportof developments in analytical atomicspectroscopy has been compiled frommore than lo00 reports received fromworld-wide correspondents who areinternationally recognised authorities inthe field and who constitute the Editor-ial Board. In addition to surveyingdevelopments throughout the worldpublished in national or internationaljournals, a particular aim has been toinclude less widely accessible reportsfrom local, national and internationalsymposia and conferences concernedwith atomic spectroscopy.Volume 1 covers the year 1971.204 pagesPrice E O OMembers of The Chemical Society may buypersonal copies at the special price of E3-00.Obtainable from-THE SOCIETY FOR ANALYTICALCHEMISTRY,(Book Department),9/10 Savile Row, London, W1X IAFSPECIALIST ABSTRACTJOURNALSpublished bySCIENCE AND TECHNOLOGY AGENCYAtomic Absorption and FlameEmission Spectroscopy AbstractsVol.5, 1973, bimonthly f24X-Ray Fluorescence SpectrometryAbstractsVol. 4, 1973, quarterly €24Thin-Layer Chromatography AbstractsVol. 3, 1973, bimonthly €24Gas Chromatography-MassSpectrometry AbstractsVol.4, 1973, quarterly €37Nuclear Magnetic ResonanceSpectrometry AbstractsVol. 3, 1973, bimonthly €30Laser-Raman Spectroscopy AbstractsVol. 2, 1973, quarterly 230X-Ray Diffraction AbstractsVol. 1-2, 1973, quarterly €30Neutron Activation Analysis AbstractsVol. 2-3, 1973, quarterly €30Electron Microscopy AbstractsVol. 1, 1973, quarterly €30Liquid Chromatography AbstractsVol. 1, 1973, quarterly f 3 0Electron Spin Resonance SpectroscopyAbstractsVol. 1, 1973, quarterly €30Sample copies on request from:SCIENCE AND TECHNOLOGY AGENCY,3 DYERS BUILDINGS, HOLBORN,LONDON, E.C.l, ENGLAND01 -405 932xiv SUMMARIES OF PAPERS I N THIS ISSUE [February, 1973Non- aqueous Atomic- absorption Spectrophotometric Analysis ofOrganonickel Complexes by a Ligand Exchange MethodA procedure is described in which diethylammonium diethyldithiocar-bamate is used to complex nickel in a mixed organic solvent, thus eliminatinginterferences due to different bonding.The interferences can also be removedby using a nitrous oxide - acetylene flame and a method has been devisedthat requires the use of only a single solvent for dissolution. The ligandexchange method should have wide application in the elimination of bondinginterferences.M. A. LEONARD and W. J. SWINDALLDepartment of Analytical Chemistry, The Queen's University of Belfast, Belfast,BT9 5AG, Northern Ireland.Analyst, 1973, 98, 133-136.A Comparison of a Spectrophotometric (Quercetin) Method andan Atomic-absorption Method for the Determination of Tin in FoodProcedures for the determination of tin in food, which involve a spectro-photometric method (with the quercetin - tin complex) and an atomic-absorption method, are described.The precision of the complete methodsand of the individual analytical steps required is evaluated, and the para-meters that influence the precision are discussed.It is concluded that while the spectrophotometric method is to bepreferred for very low tin concentrations, for instance, residues of organotincompounds, the two methods are equally useful for the determination oftin in concentrations normally found in canned foods. With both methodsrecoveries of added tin do not deviate significantly from 100 per cent. withintheir respective working ranges.ASE ENGBERGDepartment of Pesticides, Food Additives and Contaminants, National Food Institute,Copenhagen, Denmark.Analyst, 1973, 98, 137-145.The Spectrophotometric Determination of Nitrofurantoinin Blood and UrineShort PaperJANE HARRISON, D. A. LEWIS and R. J. ANCILLPharmacology Group, School of Pharmacy, University of Bath, Bath, Somerset,BA2 7AY.Analyst, 1973, 98, 146.A Method for the Detection of Microgram Amounts ofHydroxamic AcidsA rapid and simple method for the detection of small amounts ofhydroxamic acids is described. The chloroform-soluble, violet-colouredvanadium complex formed between vanadium and the hydroxamic acidsallows the detection of as little as 10 to 20 p g of hydroxamic acid in one dropof sample solution.Y. K. AGRAWALDepartment of Chemistry, Indian Institute of Technology, Powai, Bombay-76, India.Analyst, 1973, 98, 147-148

ISSN:0003-2654    

DOI:10.1039/AN97398BP019

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

FEBRUARY, I973 THE ANALYST Vol. 98, No. I163 Ionic Polymerisation as a Means of End-point Indication in Non-aqueous Thermometric Titrimetry Part I.* The Determination of Organic Bases BY E. J. GREENHOW AND L. E. SPENCER (Department of Chemistry, Chelsea College, University of London, Manresa Road, London, S . W . 3 ) A method for the thermometric titration of organic bases in non-aqueous solution, in which ionic polymerisation is used to indicate the end-point, has been evaluated for a range of aliphatic and aromatic amines, including substituted and polyfunctional amines, heterocyclic nitrogen compounds, amides and some basic sulphur and phosphorus compounds. Perchloric acid and boron trifluoride were used as titrants and a-methylstyrene and isobutyl vinyl ether were the monomers used, respectively, in conjunction with them.The precision of the method with titrants of molarities from 0.1 to 0.001 is of the order of 1.5 per cent. when a simple manual procedure involving the use of a thermometer to measure the temperature is adopted. More elaborate methods, in which the temperature is measured with a thermistor and recorded, give precisions better than 1 per cent. Sample sizes down to about 0.0001 mequiv, e.g., about 10 pg of morpho- line, which corresponds to 10 p.p.m. of morpholine in the volumes of sample solution titrated, can be determined with 0.001 M titrants. Calibration graphs show that the volume of titrant and amount of sample are linearly related in the range 0 to 3 ml of titrant. It is suggested that comparison of the results obtained when a base is titrated with the two titrants, a Brarnsted acid and a Lewis acid, can be used to investigate some of the properties of the base. THE determination of organic bases in non-aqueous solution by thermometric titration has been described by several workers.Keily and Humel studied the titration of bases in acetic acid while Forman and Hume2 used acetonitrile as the solvent; the titrants were perchloric acid in acetic acid and hydrogen bromide in acetonitrile, respectively. In both investigations temperature changes were slight when 0.1 M titrant was used, and a device reading to 0.001 "C was used for temperature measurement. Greater temperature changes, about 2 "C in the course of the titration, were achieved by Vaughan and Swithenbank3 when using a 5 M solution of hydrogen chloride in propan-2-01 as the titrant, which gave an endothermic heat of dilution at the end-point.In a method reported by Vajgand and co-worker~,~~~ the catalytic effect of the titrant, 0.25 M perchloric acid, on a mixture of water and acetic anhydride included in the sample solution causes temperature rises of about 0-5 "C at the end-point. In all of the methods described above, the molarity of the titrant or the temperature change obtainable at the end-point, or both, tends to fix a lower limit for the size of the sample that can conveniently be titrated, which, with the most sensitive method, would appear to be about 0.1 mequiv. Two recent papersss7 have briefly described procedures in which the rise in temperature that accompanies anionic and cationic polymerisation is used as a means of indicating the end-point in the non-aqueous titration of acids and bases, respectively.In these procedures, monomers that are capable of ionic polymerisation are used as solvents for the acids or bases to be determined. The temperature rise following the neutralisation of the sample by the titrant is a result of the catalytic action of free titrant on the monomer - solvent mixture. Catalysts for anionic polymerisation are, in general, strongly alkaline in character, and are therefore suitable as titrants for weak acids in non-aqueous systems. Similarly, cationic polymerisation can be initiated by catalysts with strongly acidic properties ; these catalysts, * For Parts I1 and I11 of this series, see pp.90 and 98, respectively. @ SAC and the authors. 8182 GREENHOW AND SPENCER : IONIC POLYMERISATION FOR END-POINT [AndySt, VOl. 98 in turn, are suitable reagents for the titration of bases. As many ionic polymerisations can take place at room temperature and require relatively small amounts of catalyst to initiate the highly exothermic chain reactions, sharp rises in temperature, often as great as 5 “C in 1 s, can be achieved near the end-point in these titrations. The present paper reports a detailed evaluation of the application of cationic polymerisa- tion to the thermometric titration of different classes of organic bases. Certain properties of the solvents used in ionic polymerisation studies, particularly their dielectric constants, are known to have an influence on the initiation of the polymerisation and on the rate of polymerisation.A number of solvents, covering a range of dielectric constants and “donici- ties,”8 have been investigated as solvents for the titrant and for the sample. Two titrant - monomer systems have been investigated. In the first, perchloric acid, a Brernsted acid, is used as the titrant and a-methylstyrene as the monomer-solvent. In the second, a Lewis acid, boron trifluoride, is the titrant and isobutyl vinyl ether the monomer - solvent, EXPERIMENTAL REAGENTS- a-Methylstyrene, isobutyl vinyl ether and the organic bases were laboratory-reagent grade materials and were used as received without purification. Toluene, 1,4-dioxan, 1,2-di- chloroethane and nitroethane were dried over 4A molecular sieve.Morfdioline-Analytical-reagent grade morpholine (BDH Chemicals Ltd.) , with a mini- mum assay (acidimetric) of 99 per cent., was used as a standard compound. C +I I- t Fig. 1. Thermistor bridge circuit: C, Mallory cell, Type RMlSR, 1.35 V ; D, Servoscribe potentio- metric recorder, Type RE 511; R,, sensitivity control, variable resistor, 50 R; R,, fixed resistor, 2000 R; R,, fixed resistor, 1500 R ; R, and R,, zero control, variable resistors, 1000 R ; S, switch; and T, thermistor, S.T.C. Type F23D (2000 a)February, 19731 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART I 83 Potassium hydrogen @zthaZate-AnalaR grade. Dry for 2 hours at 110 "C before use. Dry acetic acid-Prepare by adding the theoretical amount of acetic anhydride to glacial acetic acid of known water content (determined by the Karl Fischer method) and allow the mixture to stand overnight.Boron trijztoride diethyl etherate-Mix 10 volumes of laboratory-reagent grade boron trifluoride with 1 volume of diethyl ether and add about 2 g of calcium hydride to each 100 ml of the mixture. Distil the dried mixture and take a middle fraction, the boiling-point of which is above 120 "C. Boron tri$uoride diethyl etherate, 0.1 M in dioxan-Standardise this solution against a solution of morpholine (20 mg) in toluene (2 ml). Perchloric acid, 0.1 M in dry acetic acid-Measure 8-5 ml of AnalaR grade perchloric acid (71.0 to 73.0 per cent.) into a 1-litre calibrated flask and add 100 ml of dry acetic acid and 15 ml of acetic anhydride slowly with constant stirring and cooling.Dilute to the mark with dry acetic acid and leave for 24 hours in the dark. Standardise the solution against solutions of potassium hydrogen phthalate in dry acetic acid and morpholine in toluene. Prepare other standard solutions of perchloric acid by adding the appropriate amount of the 0.1 M solution in dry acetic acid to the solvent of choice, and other standard solutions of boron trifluoride by diluting the 0.1 M solution in dioxan in a similar way. APPARATUS- A. Manual method-Use a -5 to +SO "C thermometer graduated in 0.1 "C, either a 10-ml Dewar beaker or a 50-ml tall-form beaker, a 5-ml burette graduated in 0.01 ml, with the tip drawn out to a capillary about 1 inch long, and a magnetic stirrer. B. Semi-automatic method-Use the apparatus of Method A with a thermistor for tem- perature measurement instead of the thermometer.The thermistor (S.T.C., Type F23D) forms part of a bridge circuit (Fig. l), which is connected to a millivolt chart recorder with full-scale ranges of 5, 10, 20, 50 and 100mV and a chart speed of 30 mmmin-l. C. Automatic method-Use the thermistor system for temperature measurement, a 10-ml Dewar beaker to contain the sample, and a motor-driven Agla micrometer syringe (0.5 ml) for the titrant feed. The switches for the syringe motor and the recorder-chart drive are coupled together to synchronise titrant addition with temperature measurement. PROCEDURE A. MANUAL METHOD- Prepare a solution of the base in a suitable solvent, e.g., toluene, acetone, nitroethane, 1,2-dichloroethane or acetic acid (dry).The concentration will depend on the titrant con- centration, thus 2 ml of the solution should contain about 0.2 mequiv of base when the 0.1 M titrant is used, about 0.02 mequiv with 0.01 M titrant, and so on. Transfer by pipette 2 ml of the sample solution into the beaker, add 10 ml of monomer (2 to 5ml if the 10-ml Dewar beaker is used), stir the solution, in which the thermometer bulb is immersed, for 1 minute, then add titrant at the rate of about 0.5 ml min-l to within 0.3 ml of the end-point, noting the temperature at &minute intervals, and complete the titration with addition of titrant at a rate not exceeding 0.2 ml min-1, noting the temperature at 15-s intervals. At rates significantly greater than 0.2 ml min-1, high titration values are obtained owing to overshooting of the end-point.Addition of titrant at rates slower than 0.2 ml min-l gives only a small improvement in precision with the more concentrated titrants, and with the less concentrated titrants can result in loss of end-point sharpness. When the temperature exceeds 35 "C, remove the thermometer from the solution so as to avoid damaging it, and pour the solution to waste after diluting it with about two volumes of acetone. B. SEMI-AUTOMATIC METHOD- Use a procedure that is similar to that used in Method A, but replace the thermometer by a thermistor and record the temperature changes on the millivolt chart recorder. Start a stop-clock synchronously with the recorder-chart drive in order to relate the titrant volume, which is read off at appropriate times, to the temperature on the recorder chart.In practice, it is necessary only to note the time and the volume corresponding to the required inflection point on the chart record.84 GREENHOW AND SPENCER IONIC POLYMERISATION FOR END-POINT [A?W&d, VOl. 98 C . AUTOMATIC METHOD- Use a procedure that is similar to that used in Method €3 but add titrant at a constant rate of 0.2 ml min-l from the motor-driven syringe. Calibrate the recorder chart in millilitres of titrant in order to read off the titrant volume directly. DETERMINATION OF END-POINT- The titrant volume at the end-point is measured in three ways. (i) As the volume corresponding to the "upturn" temperature where the titration curve leaves the tangent drawn to its horizontal part.In Method A a rise in temperature of at least 0.1 "C is needed in order to locate this end-point. (ii) From the intersection point of tangents to the two component parts of the tem- perature - volume curve. For precision, this measurement requires the parts to have linear sections in the vicinity of the end-point. (iii) As the volume corresponding to the temperature following the first temperature increase of 0-3 "C or more, in a period of 15 s, when the rate of titrant addition is between 0.1 and 0.3 ml min-l. Methods (ii) and (iii) give approximately the same result, and method (iii) can be used as a rapid means of end-point determination in conjunction with Method A. Method (i) is the preferred method when applicable, as the volume of titrant thus measured corresponds closely to that obtained by potentiometric titrimetry. RESULTS AND DISCUSSION In an earlier paper,6 it was shown that the perchloric acid-a-methylstyrene system could be used for the determination of primary, secondary and tertiary aliphatic amines, represented by n-butylamine, morpholine and triethylamine, respectively, and it was claimed that a solution of boron trifluoride in dioxan was also a suitable titrant when used in con- junction with isobutyl vinyl ether as the monomer.The applicability of the latter titrant to the determination of these amines has been confirmed. The precision of the manual method of thermometric titration (A) has been determined by using both titrants in concentrations in the range 0.1 to 0.001 M (Table I). In general, TABLE I RESULTS FOR PRECISION FROM THE THERMOMETRIC TITRATION OF MORPHOLINE WITH 0.1 TO 0.001 M SOLUTIONS O F PERCHLORIC ACID AND BORON TRIFLUORIDE Coefficient of variation, Titrant Method per cent.- of End- Mono- Morpho- No. of Mean titra- point mer/ line/ titra- titre/ Standard Single Mean Nominal molarity Solvent* tiont method? ml mg tions ml deviation points value Perehlorie acid (monomer : wmethy1styrene)- - 0.1 A A (ii) 10 10 5 1.27 0.016 1.29 0.58 0.1 A A (ii) 10 20 6 2.52 0.040 1-68 0.71 0.025 A A (ii) 15 7 3 3.91 0.056 1.42 0.82 0.01 A A (ii) 10 2 4 3.38 0.083 2-44 1.22 2 0.2 3 1.30 0.010 0.77 0.45 0.2 3 1.67 0.015 0.90 0.52 0.002 A + X (1 + 49) A (2) 0.002 A + N (1 + 49) €3 (2%) Boron trifluoride (monomer : isobutyl vinyl ethev)- 0.1 D A (ii) 10 10 5 1-04 0.011 1.09 0.49 0.1 D A (ii) 10 25 5 2.42 0.015 0.63 0.28 0.01 D A (id) 10 2 4 3.33 0.038 1-14 0.57 0.2 3 1-80 0.026 1-39 0.80 0.002 D + C (1 + 49) A (i) 2 0.2 4 1.44 0-034 2.36 1.18 0.1 3 1-62 0.030 1.85 1.07 5 10 4 0-867 0.005 0.68 0.29 2.5 5 0.436 0.002 74 0.63 0.28 0.002 D + N (1 + 49) A ($2) 0.001 D + N (1 + 49) A (2) 0.1 D B (4 0.1 D C (ii) * A = acetic acid; C = acrylonitrile; D = dioxan; N = nitroethane; and X = 1,2-dichloroethane.t See Experimental. Figures in parentheses refer to proportions by volume.February, 19731 INDICATION I N NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART I 85 the titration values show coefficients of variation of single results about the mean to be of the order of 1.5 per cent. and coefficients of variation of the mean value to be less than 1 per cent.Results for precision have also been calculated from values obtained with the semi- automatic method (B) and the automatic method (C) ; these results are also shown in Table I. As might be expected, Methods B and C gave results with higher precision than those obtained with the manual method by using titrants of the same molarity. However, the improvement in precision is not as marked as one would expect, considering the large size of the bulb (20 x 5 mm) of the thermometer used in Method A, and the fact that with the 10-ml beaker the bulb is immersed only to one third of its length in the titration solution. The semi-automatic method offers some advantage over the fully automatic method in that, with the manually operated titrant feed, it is possible to add the bulk of the titrant rapidly and the remainder at a slow rate so as to avoid over-running of the end-point.All of the precision experiments were carried out by using standard solutions of morpholine in toluene; 1 and 2-ml aliquots were taken with grade A pipettes (B.S. 1583:1961), and sampling errors arising from their use will, of course, affect the over-all precision of the determination. Calibration studies with morpholine have shown that sample size and titre are linearly related in the ranges 0.05 to 0.3 mequiv of sample (about 5 to 30 mg) with 0.1 M titrant, 0.0005 to 0.003 mequiv of sample (about 50 to 300 pg) with 0.001 M titrant, and in the corresponding ranges with titrants of intermediate molarity.The morpholine samples for the calibration experiments were added to the monomer as solutions in 1 ml of toluene. It can be seen, therefore, that with the 0*001 M titrant a 50-pg amount of the organic base could be titrated as a 50 p.p.m. solution in toluene. With this amount, titres of about 0-5 ml were obtained, and it can be concluded that concentrations as low as 10 p.p.m. should easily be detected. Titrants more dilute than 0.1 M were prepared by adding solvents to the 0.1 M solutions, Further dilution of the 0.1 M boron trifluoride solution with dioxan, and 0.1 M perchloric acid solution with dry acetic acid, down to concentrations of 0.01 M, gave satisfactory titrants with respect to end-point sharpness, but at lower concentrations the end-points became less I I I I I Perchloric acid titrandm1 (1 division = 1 ml) Fig.2. Effect of titrant molarity and titrant solvent on the shape of the thermometric titration curve : perchloric acid titrants (morpholine sample). a b c d e f Rlolarity . . . . . . 0.1 0.01 0.002 0.002 0.002 0.001 Morpholine/mg . . . . 10 2 0.2 0.2 0.2 0.1 Diluent for 0.1 M HC10, in CH,COOH . . . . - A A N X X a-Methylstyrene/ml . . 10 10 2 2 2 2 A = acetic acid; N = nitroethane; and X = 1,2-dichloroethane86 GREENHQW AND SPENCER : IONIC POLYMERISATION FOR END-POINT [AfiUZySt, VOl. 98 satisfactory (see Figs. 2 and 3). This difficulty was overcome by using either nitroethane or 1 ,Z-dichloroethane as the diluent ; it was then possible to obtain significant rises in tem- perature at the end-point with 0.001 M titrants.Acrylonitrile also proved to be a satisfactory diluent, but only for the boron trifluoride titrant. Although the rise in temperature at the end-point with nitroethane as the diluent was usually greater than could be obtained with 1,Z-dichloroethane or acrylonitrile, the endotherm resulting from the dilution of the monomer made it difficult to determine the end-point accurately. In contrast, sharp end-points were obtained with titrants diluted with 1,2-dichloroethane, and titration curves of similar shape were obtained with titrants prepared by diluting the 0.1 M boron trifluoride titrant only with acrylonitrile. I t t s I I 1 I I I Boron trifluoride titranthl (1 division = 1 ml) Fig. 3. Effect of titrant molarity and titrant solvent 011 the shape of the thermometric titration curve : boron trifluoride titrants (morpholine sample).a b c d e f g h Molarity . . .. . . 0.1 0.01 0.002 0.002 0.002 0.001 0.001 0.001 Morpholinelmg . . . . 10 2 0.2 0.2 0.2 0.1 0.1 0.1 Diluent for 0.1 M BF3.(C,H,),0 in dioxan - D N X C D N X Isobutylvinyl etherlml . . 10 10 2 2 2 2 2 2 D = dioxan ; N = nitroethane ; X = 1,2-dichloroethane ; and C = acrylonitrile The effect of solvents on the rate of cationic polymerisation has been the subject of considerable investigation (see, for example, reference 9). Increasing the dielectric constant of a catalyst solution promotes the separation of ion pairs and allows the cation and monomer to react more readily. Consequently, highly polar solvents, such as nitroethane, might be expected to increase both the rate of initiation and of propagation of the polymerisation process.Although the rate of polymerisation is lower in dichloroethane, the absence of a large dilution endotherm, which tends to nullify any temperature rise, results in a sharper end-point inflection than is possible with nitroethane-based titrants. Thus with titrants diluted with 1,2-dichloroethane, the “upturn” temperature at the end-point [method (41 can be measured reasonably accurately, while with titrants diluted with nitroethane only the less reproducible tangent-intersection end-point [method ( 4 1 can be obtained. The ineffectiveness as titrants of 0.002 and 0-001 M solutions of boron trifluoride in dioxan probably results from the Lewis-base properties of dioxan, which reduce the activity of this catalyst.Acrylonitrile appears to have a similar effect on perchloric acid, but not on boron trifluoride for which it is a satisfactory diluent. The temperature rise indicating the end-point of the thermometric titration occurs when a critical concentration of catalyst is exceeded. Blank titrations show that thisFebruary, 19731 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART I 87 concentration is reached with less than 0.05 ml of 0.1 M titrant under the conditions used, but with 0401 M titrant about 0.4 ml is required. The amount of titrant needed to reach a required concentration will depend on the volume of the titration solution, and it has been found that with 0.001 M titrants it is desirable to limit the volume of monomer to about 2 ml.The sharp end-points obtained with 0.001 M titrant (Figs. 2, f and 3, h) would suggest that even more dilute titrants, such as 0.0001 M concentration, could be used, and organic bases in amounts as low as 0.000 01 mequiv, e.g., about 1 pg or less of morpholine, could be determined. However, with 0.0001 M titrant, there would be difficulties in achieving the critical catalyst concentration needed to initiate polymerisation, and it would probably be necessary to use a volume of monomer of much less than 2 ml, thereby limiting the amount of heat available from polymerisation. At this level, then, the manual titration method would no longer be suitable and it would be desirable to have constant temperature conditions in the vicinity of the apparatus. 1 2 0.1 M Boron trifluoride in dioxadml Fig.4. Effect of water on the thermometric titration of morpho- line (10 mg in 1 ml of toluene plus 10 ml of isobutyl vinyl ether) with 0.1 M boron trifluoride in dioxan (titration Method A): a, no water added; b, + l o mg of water; c, +22 mg of water; d, +95 mg of water; e, +120 mg of water; f, +104mg of water + 0.5 g of molecular sieve 4A; and g, +73 mg of water (only 2 ml of isobutyl vinyl ether). Points on curves have been omitted for clarity Small amounts of impurities can have an adverse effect on polymerisation processes that proceed by chain-reaction mechanisms. In an earlier papera it was shown that both water and methanol inhibited the polperisation that is catalysed by perchloric acid, but that a fairly high proportion of methanol could be tolerated and water could be eliminated by addition of molecular sieve to the titration solution.The presence of water also affects the efficiency of the boron trifluoride catalyst. As shown in Fig. 4, it reduces the sharpness of the end-point inflection but not as markedly as with perchloric acid. In addition, there is a “drift” of the end-point to a higher titre; however, this drift is small even when the mass88 [Analyst, Vol. 98 of water is equal to that of the morpholine in the sample, and can be reduced by increasing the volume of the monomer, i.e., by decreasing the concentration of water in the monomer, or, of course, by reducing the sample size. Methanol has a much smaller effect on boron trifluoride than on perchloric acid, and sharp end-points were obtained in titrations of 1 + 100 morpholine - methanol mixtures. Ketones, aldehydes and esters do not appear to interfere in the titration procedure.A range of organic bases that were titrated by using the two titrant - monomer systems, with 0.1 M titrant in each instance, is listed in Table 11. For these determinations, solutions of titrants were standardised with solutions of morpholine in toluene. Perchloric acid was also standardised against a solution of potassium hydrogen phthalate in dry acetic acid, by using both an indicator (crystal violet) and the thermometric method to measure the end-point. The results obtained for nominally 0.1 M perchloric acid were similar for all three methods. GREENHOW AND SPENCER: IONIC POLYMERISATION FOR END-POINT TABLE I1 ORGANIC BASES TITRATED WITH 0.1 M PERCHLORIC ACID IN ACETIC ACID AND Conditions: 0.1 mequiv of base in 1 ml of solvent (toluene, dichloroethane, nitroethane, acetone or acetic acid) added to 10ml of the appropriate monomer in a 50-ml beaker and titrated by using Method A BORON TRIFLUORIDE DIETHYL ETHERATE IN DIOXAN Aliphatic amines- n-Butylamine (1 : 1 : 1) ; morpholine (1 : 1 : 1) ; triethylamine (1 : 1 : 1) ; tris(hydroxymethy1)- methylamine (1 : 1 : 0) ; and 6-aminocaproic acid (1 : 1 : 1) Pyridine (1 : 1 : 1) ; a-picoline (1 : 1 : 1) ; 4-vinylpyridine (1 : 1 : 1) ; quinoline (1 : 1 : 1) ; 8-hydroxy- quinoline (1 : 1-4 : 1) ; and 2,6-lutidine (I : 1 : 0.9) p-Toluidine (1 : 1 : 0-7) ; p-nitroaniline (1 : 1 :0) ; and P-hydroxyaniline (1 : 1.2 : 0) o-Phenylenediamine (2 : 2 : 1) ; m-phenylenediamine (2 : 2 : 1.3) ; p-phenylenediamine (2 : 2 : 1.5) ; 2-amino-4-methylpyridine (2 : 1 : 1.3) ; 8-aminoquinoline (2 : 2 : 1.3) ; and hydrazobenzene Pyridine derivatives- Aniline derivatives- Difunctional aromatic amines- (2 : 2 : 0) Heterocyclic nitrogen compounds- Imidazole (2 : 1 : 1.2) ; benzimidazole (2 : 1 : 1) ; benzotriazole (3 : 1 : 1) ; quinoxaline (2 : 1.4 : 0.5) ; and 2,3-dichloroquinoxaline (2 : 0.8 : 0) Acetamide (1 : 1 : 0) ; dimethylformamide (1 : 1 : 0) ; diethylformamide (1 : 1 : 0.6) ; NN-dimethyl- acetamide (1 : 1 : 0.4) ; dimethyl sulphoxide (1 : 1 : 0-7) ; and hexamethylphosphoramide ( 1 : 1.5: 1)* Figures in parentheses following the name of the base denote the theoretical number of basic functional groups in the molecule, the number of groups titrated with the 0.1 M perchloric acid and the number of groups titrated with the 0.1 M boron trifluoride, respectively.* On the basis of the amido groups the functionality will be 3. Amides and sulphur and phosfihorus derivatives- Both perchloric acid and boron trifluoride titrants can be used to determine primary, secondary and tertiary aliphatic amines, and simple pyridine and quinoline derivatives. Only perchloric acid reacts stoicheiometrically with the monofunctional aniline derivatives examined ; boron trifluoride gives titration values ranging from zero, with 9-nitroaniline, to about 70 per cent. of the theoretical requirement, with 9-toluidine. With difunctional organic bases the titration values obtained depend on the amount of interaction of the two groups, i.e., the influence each group has on the reactivity of the other.With perchloric acid both amino groups in o-, m- and 9-phenylenediamine are deter- mined, while with boron trifluoride only one of the groups in o-phenylenediamine is deter- mined and, under the titration conditions used, titration values with the m- and $-isomers are obtained corresponding to about one and a half amino groups, which suggests that the forces of attraction for the boron trifluoride exerted by the monomer and the second amino group of the m- and p-isomers are similar. Both titrants can be used to determine 'the amino group in 6-aminocaproic acid (6-amino- n-hexanoic acid) but application of the method to aliphatic amino-acids in general has been found to be influenced by the solubility of the acids in the solvent system and low resultsFebruary, 19731 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY.PART I 89 were obtained with glycine, for example. Boron trifluoride reacts stoicheiometrically, in a 1 : 1 ratio, with 8-hydroxyquinoline but does not react with p-hydroxyaniline. On the other hand, perchloric acid reacts with both compounds non-stoicheiometrically in excess of the 1: 1 ratio, indicating that some reaction occurs with the hydroxyl groups. Both groups in hydrazobenzene can be titrated with perchloric acid but boron trifluoride does not react. With 2-amino-4-methylpyridine, perchloric acid reacts stoicheiometrically in a 1 : 1 ratio, whereas with 8-aminoquinoline, in which the functional groups are on separate rings, the reaction is in the ratio 2 : 1.Rather surprisingly, boron trifluoride reacts non-stoicheio- metrically in a ratio exceeding 1 : 1 with both of these difunctional bases. The cyclic bases imidazole, benzotriazole, quinoxaline and 2,3-dichloroquinoxaline have been examined. Perchloric acid reacts in a 1 : 1 molar ratio with the first two compounds, but non-stoicheiometrically with the other two, the ratios being about 1.4: 1 with quinoxaline and only about 0 4 : l with the dichloro compound. Boron trifluoride does not react with this last compound, as might be expected with a compound containing two strongly de- activating halogen atoms. With quinoxaline the reaction occurs in a molar ratio of about 0.5: 1, but with imidazole the ratio exceeds 1 : 1, in contrast to the ratio of 1 : 1 with perchloric acid.In contrast, benzotriazole does not react with boron trifluoride. Some compounds that have high electron-pair donicitiess have been titrated. Dimethyl sulphoxide, diethylformamide and NN-dimethylacetamide react stoicheiometrically with perchloric acid but sub-stoicheiometrically with boron trifluoride. Hexamethylphosphor- amide reacts with perchloric acid and boron trifluoride in the ratios of 1 : 1.5 and 1 : 1, respec- tively, which accords with the reported high donicity of this compound. Dimethylformamide and acetamide, which are both lower on the donicity scale, react stoicheiometrically with perchloric acid but do not react with boron trifluoride.The reactions described in this paper are competitive, the organic bases competing with the monomer for the titrant - catalyst. With perchloric acid in combination with a-methyl- styrene, the reactivity of organic bases is, in general, so much higher than that of the monomer that stoicheiometric reaction of the base with the titrant occurs before polymerisation. With boron trifluoride in conjunction with isobutyl vinyl ether, however, the difference in reactivity between many bases and the monomer is not so marked and sub-stoicheiometric reactions are more common. It is clear that different results would be obtained in the sub-stoicheio- metric reactions if other monomer - catalyst combinations were used. We have examined styrene and isoprene as possible alternative monomers in combination with the present catalysts but both were unsatisfactory under the conditions used. When sub-stoicheiometric reactions occur, i.e., when the reactivities of the organic base and the monomer with respect to the titrant are similar, the process is kinetically controlled. This effect has been noted with 9-toluidine for which the reaction ratio with 0.1 M boron trifluoride solution is 0.7 when 10 mg of sample are titrated in 10 ml of monomer and 0-58 when 20 mg of sample are titrated in 10 ml of monomer; to obtain more exact information about the reactivities and related properties of the bases it will be necessary to carry out a detailed kinetic investigation. This thermometric method can therefore be used to study the basic properties and, indirectly, the structures of organic bases. The reaction ratios given in Table I1 are an approximate indication of the basic properties of the organic bases examined when non- stoicheiometric reaction has occurred. For example, the results show that e-toluidine is more basic than 9-nitroaniline, the ratios being 0.7 and zero, respectively, with boron trifluoride titrant, under the conditions used for the titrations. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES Keily, H. J., and Hume, D. N., Analyt. Chem., 1956, 28, 1294. Forman, E. J., and Hume, D. N., TaZanta, 1964, 11, 129. Vaughan, G. A., and Swithenbank, J. J., Analyst, 1967, 92, 364. Vajgand, V. J., and Ga&l, F. F., Talanta, 1967, 14, 345. Vajgand, V. J., Kiss, T. A., GaAl, F. F., and Zsigrai, I. J., Ibid., 1968, 15, 699. Greenhow, E. J., Chew. & Ind., 1972, 466. Gutmann, V., Chem. Brit., 1971, 7 , 102. Plesch, P. H., Editor, “The Chemistry of Cationic Polymerisation,” Pergamon Press, London, 1963. Received May 16lh, 1972 Accepted September 25th. 1972 -, Ibid., 1972, 422.

ISSN:0003-2654    

DOI:10.1039/AN9739800081

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

90 Analyst, February, 1973, Vol. 98, pp. 90-97 Ionic Polymerisation as a Means of End-point Indication in Non-aqueous Thermometric Titrimetry Part II.* The Determination of Organic Acids BY E. J. GREENHOW AND L. E. SPENCER (Defiartment of Chemistry, Chelsea College, University of London, Manresa Road, London, S. W.3) A method for the thermometric titration of organic acids in non-aqueous solution, involving the ionic polymerisation of acrylonitrile to indicate the end-point, has been evaluated for a range of mono- and polyacidic compounds, including phenols, triazine derivatives and tannic acid. In addition to acrylonitrile, methyl acrylate and dimethyl itaconate can be used as monomers for the end-point indication. A number of titrant - catalysts have been examined, including tetra-n-butylammonium hydroxide, n-butyllithium and potassium hydroxide. The precision of the method ranges from about 0.5 per cent.with 0.1 M titrant, to 2.7 per cent., with 0.001 M titrant, by using the manual and semi-automatic methods described in Part I. Sample sizes down to about 0.0001 mequiv, e.g., about 10 pgof benzoic acid, which corresponds to 100 p.p.m. of benzoic acid in the volumes of sample solution titrated, can be determined with 0.001 M titrant. Calibration graphs show the volume of titrant and mass of sample to be linearly or almost linearly related in the range 0 to 2 ml of titrant. Comparison of the titration values obtained by using the acetone method and ionic polymerisation with potassium hydroxide and tetra-n-butylam- monium hydroxide solutions as titrants enables one to differentiate between acidic groups of different ionicstrengths in the 10 to 12 pK, region.THE difficulty in obtaining a sharply defined end-point in the non-aqueous thermometric titration of weak acids, such as phenols, has been pointed out by Vaughan and Swithenbank.1 These authors showed that the end-point could be clearly defined by using acetone as a thermometric end-point indicator. Acetone is used as the solvent for the sample of acid, and, after the latter has been neutralised by the alkaline titrant, further addition of titrant catalyses the exothermic dimerisation of the acetone and a sharp rise in temperature occurs. The general principles of this approach to thermometric titrimetry, which has been given the name “catalytic thermometric titration,” have been discussed by Vajgand, GaAl, Zarnic, Brusin and Velimirovic.2 Catalytic thermometric procedures in which highly exothermic ionic polymerisation processes are used to indicate the end-point in titrations of organic acids and bases in non- aqueous solution have been discussed in Part I3 and in earlier paper^.^^^ When acrylonitrile is used as the solvent for an organic acid it undergoes polymerisation after the acid has been neutralised by the alkaline titrant, if certain strongly basic titrants such as potassium hydroxide in propan-2-01 and tetra-n-butylammonium hydroxide in toluene - methanol are used, provided that a sufficient excess of the titrant is added. With 0.1 M titrants rises in temperature exceeding 10 “C can be obtained with an excess of titrant of about 0.05 ml.The present paper gives a more detailed evaluation of the procedure described in an earlier paper.4 The precision and sensitivity of the method have been studied, as well as its application to a range of mono- and polyfunctional organic acids. In addition to acrylo- nitrile, methyl acrylate and dimethyl itaconate have been investigated as monomer - solvents. A number of compounds known to be effective catalysts for anionic polymerisation have been examined as possible titrants ; those found to be suitable include n-butyllithium and potassium t-butoxide, in addition to the titrants mentioned above. Results obtained in the titration of polyacidic compounds by using acrylonitrile as the end-point indicator and potassium hydroxide and tetra-n-butylammonium hydroxide as titrants have been compared with those obtained by using the acetone procedure of Vaughan and Swithenbank.1 * For Parts I and 111 of this series, see pp.81 and 98, respectively. @ SAC and the authors.GREENHOW AND SPENCER EXPERIMENTAL REAGENTS- 91 Laboratory-reagent grade acrylonitrile, methyl acrylate, toluene, methanol, propan-2-01, 2-methylpropan-2-01, acetone, dimethylformamide and dimethyl sulphoxide were dried over molecular sieve 4A before use. Dimethyl itaconate-Commercial material supplied by Pfizer Ltd. was used as received. Benzoic acid-AnalaR grade (BDH Chemicals Ltd.) was used as received. Tannic acid-Laboratory-reagent grade (BDH Chemicals Ltd.) material (relative mole- cular mass 1701.23 and empirical formula C76H5@46) was used.Other organic acids were laboratory-reagent grade materials and were used without further purification. Tetra-n-butylammonium hydroxide, 0- 1 M in toluene - methanol-Laboratory-reagent grade (BDH Chemicals Ltd.). This reagent was used as received. Prepare more dilute solutions by adding toluene - propan-2-01 (3 + 1) mixture to the 0.1 M reagent. Tetra-n-butylammonium hydroxide solutions, 0.1 to 0.001 M-Standardise the solutions against benzoic acid in dimethylformamide by the thermometric method. Potassium hydroxide, 0.1 M solution in propan-2-ol-Standardise this solution against benzoic acid, with phenolphthalein as indicator, and also by the thermometric method. Potassium t-butoxide, 0.1 M solution in 2-methyl~ropan-2-ol-Prepare this solution by dissolving potassium metal in 2-methylpropan-2-01 and standardise the solution against benzoic acid in dimethylformamide by the thermometric method.n-Butyllithium, 0.1 M solution in toluene-Prepare this solution by diluting the 16 per cent. solution in hexane (Koch-Light) with toluene and standardise it against benzoic acid in dimethylformamide by the thermometric method. PROCEDURE- The manual and semi-automatic methods (Methods A and B) described in Part 1 3 were used with the following modifications. Titrate organic acids as 0-1 N solutions in toluene or dimethylformamide when 0.1 and 0-025 M titrants are used, and as 0.01 N solutions when 0.01 and 0.001 M titrants are used. In precision determinations add the sample as an aliquot of a standard solution with grade A pipettes or, for amounts of less than 1 ml, with an Agla micrometer syringe.With 0.1 and 0-025 M titrants carry out the titrations in a 50-ml beaker insulated with polystyrene foam or in the closed apparatus (capacity 15 ml) (Fig. 1) by using 10 and 5 ml of monomer, respectively; with 0.01 and 0-001 M titrants use the closed apparatus (capacity Scales apparatus 15-ml 1 crn apparatus 1 1 cm Magnetic stirrer Fig. 1. Titration apparatus92 GREENHOW AND SPENCER : IONIC POLYMERISATION FOR END-POINT [Analyst, VOl. 98 5 ml) and 2 and 1 ml of monomer, respectively. Use the methyl acrylate and dimethyl itaconate monomers as 1 + 1 mixtures with dimethylformamide or dimethyl sulphoxide, and not as the pure monomers. End-points are measured as in Part I at the “upturn” temperature [method (i)], at the intersection point of the tangents to the two component parts of the titration curve [method ( 4 1 or by the method of Vaughan and Swithenbank,6 in which the end-point is taken to be the point where the tangent to the main heat rise leaves the curve at its lower temperature end (see Fig. 1, reference 6).All three methods give values showing similar precision, but that of Vaughan and Swithenbank gives the best stoicheiometry and is preferred when a tangent can be drawn unambiguously. RESULTS AND DISCUSSION The precision of the method has been established by titrating aliquots of standard solutions of 3,5-xylenol and benzoic acid in toluene with 0.1, 0.025, 0.01 and 0.001 M tetra- n-butylammonium hydroxide solutions, and the results obtained are summarised in Table I.Precisions are expressed as coefficients of variation of single points about the mean, and range from about 0.5 per cent. for 0.1 M titrant to 2-7 per cent. for 0.001 M titrant. Co- efficients of variation of the means themselves, which depend on the number of replicate titrations, are correspondingly lower. Higher precisions could, no doubt, be attained by adding the sample by mass instead of by volume. Most of the determinations were carried out by using the manual procedure (A) in which titrant is added from a burette and the temperature is measured with a thermometer. Some improvement in precision was obtained by using the semi-automatic procedure (B) in which the temperature is measured with a thermistor and recorded, but this improvement was not marked.TABLE I RESULTS FOR PRECISION FROM THE THERMOMETRIC TITRATION OF BENZOIC ACID AND 3,5-XYLENOL WITH 0.1 TO 0.001 M SOLUTIONS OF TETRA-n-BUTYLAMMONIUM HYDROXIDE WITH ACRYLONITRILE AS END-POINT INDICATOR Titrant Titra- molarity tion 0-1 A 0.025 A 0.026 A 0.01 A 0.00 1 A 0.1 B 0.01 B * See Procedure. and the remainder in Coefficient of variation, Method* per cent. & Mean F- End- Mono- Sample,’ titre/ Standard Single Mean point mer/ml mgt n# ml deviation points value (ii) 6 B,12*6 4 1.075 0.0068 0.537 0.268 (ii) 10 x , 4 4 1.433 0.013 0.878 0.439 (ii) 10 x , 1 0 6 3.236 0.051 1-64 0.690 2 B, 1.2 5 1.222 0.022 1.78 0.795 1 B,O*036 4 0.810 0.022 2.72 1.36 5 B,12-5 4 1-06 0.0044 0.416 0.208 2 B, 1.2 5 1.225 0.018 1.47 0.660 (i) (4 (4 (2) Experiments with 10 ml of monomer were carried out in the 60-ml beaker the closed apparatus (Fig.1). t B = benzoic acid; X = 3,5-xylenol. n = number of determinations. The effect of carbon dioxide and moisture in the atmosphere contributes to the total error in determinations when the 50-ml beaker is used. This effect is great with 0.001 M titrant and it was not possible to obtain reproducible results when an open container was used for the titration. Sharp, reproducible end-points were, however, obtained when a closed system that was purged with dry nitrogen was used (Fig. 1). Typical titration curves obtained with titrants of different molarities are shown in Fig. 2. Although satisfactory results could be obtained with 15 ml of acrylonitrile and a total volume of monomer plus sample of up to about 30 ml when 0.1 and 0.025 M titrants were used, with the 0.01 and 0.001 M titrants it was necessary to take smaller amounts of monomer and sample solution to achieve the required concentration of the catalyst for initiation of polymerisation at the end-point.Suitable volumes were 2 ml of acrylonitrile and not more than 1 ml of sample solution, and 1 ml of acrylonitrile and not more than 0.1 ml of sampleFebruary, 19731 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART 11 93 solution, for the 0.01 and 0.001 M titrants, respectively. The blank titration value, which gives a measure of the amount of catalyst needed to initiate polymerisation under the con- ditions used, ranges from less than 0.05 ml with 0.1 M titrant to about 0.3 ml with 0901 M titrant. Tetra-n-butylammonium hydroxide reagent/ml ( 1 division = 1 mi) Fig.2. Thermometric titration of benzoic acid with 0.1 to 0.001 M tetra-n-butylammonium hydroxide reagent. a b C d Molarity . . . . 0.1 0.01 0.001 0.001 Acrylonitrile/ml . . 10 2 1 1 Apparatus . . .. A B B C Benzoic acid/mg . . 12.2 1.22 0.036 0.036 A = 60-ml beaker; B = 12-ml beaker; and C = 6-ml closed apparatus (Fig. 1) With the more dilute titrants one might expect the volume of “free” titrant required to initiate polymerisation to increase significantly with increase in titrant volume , because any volume increase effectively reduces the over-all concentration of the catalyst. If this was so the calibration graph would be exponential in form.However, calibration graphs for all the titrants studied were found to be linear, or almost linear, in the range 0 to 2 ml of titrant, even though a titrant volume of 2 ml represents a three-fold increase in total volume when 1 ml of monomer is used. Fig. 3 shows the calibration graph for benzoic acid and nominally 0.001 M (actually 0.000 65 M) tetra-n-butylammonium hydroxide solution. I 1 ! 0.001 M Tetra-n-butyiammonium hydroxide reagent/ml Fig. 3. Calibration graph for the titra- tion of benzoic acid with 0.001 M tetra- n-butylammonium hydroxide reagent94 GREENHOW AND SPENCER : IONIC POLYMERISATION FOR END-POINT [Analyst, vol. 98 It was noted earlier4 that water and methanol inhibited the polymerisation process but that, with 0.1 M titrant, about 1 per cent.of water and 5 per cent. of methanol could be tolerated in the solutions to be titrated. With 10-mg samples in JOml of solution this is 25 and 125 times the sample size, respectively. Tertiary amines and polar solvents, such as dimethylformamide and dimethyl sulphoxide, do not inhibit polymerisation but primary and secondary amines undergo an exothermic addition (cyanoethylation) with acrylonitrile, which reduces the end-point sharpness (Fig. 4). With 0.1 M titrant and 10 ml of acrylonitrile this effect does not become serious, from the aspect of end-point determination, until the amine to sample ratio approaches 100 : 1 with morpholine. In addition to acrylonitrile, other monomers that are capable of undergoing anionic polymerisation have been examined as end-point indicators.Satisfactory initiation of poly- merisation for the titration could not be achieved with styrene, isoprene or methyl meth- acrylate, but methyl acrylate and dimethyl itaconate polymerised readily when dissolved in dimethylformamide or dimethyl sulphoxide. Successful titrations were carried out with potassium hydroxide in propan-2-01 and tetra-n-butylammonium hydroxide as titrant - catalysts. The titration curves were similar to those obtained with acrylonitrile (Fig. 5). Dimethyl itaconate is an attractive monomer for routine analysis in that it is non-toxic and, unlike methyl acrylate, has a tolerable odour. .t i 1 1 I I I 0.1 M Tetra-n-butylammonium hydroxide reagent/ml (1 division = 1 ml) Fig. 4. Effect of morpholine on the titration of benzoic acid with 0.1 M tetra-n-butylammoniuni hydroxide reagent.Conditions: 12 mg of benzoic acid and 5 nil of acrylonitrile. Morpholine/mg: a, 75; b, 160; c, 200; d, 320; e , 430; and f, 530. Arrow indicates theoretical end-point Tetra-n-butylammonium hydroxide was found to be a satisfactory titrant - catalyst for most of the monofunctional acids determined. It has the advantage that with many acids the salts formed are soluble in the titration solution, and the question of occlusion of sample in precipitated salts does not arise. Potassium hydroxide in propan-2-01 and potassium t-butoxide in 2-methylpropan-2-01 are also satisfactory titrant - catalysts but the potassium salts formed in the titrations are generally insoluble and sample occlusion can occur.n-Butyl- lithium, a well established catalyst for anionic polymerisation, does not polymerise acrylo- nitrile, presumably because of complex formation, but it is an effective catalyst for the polymerisation of dimethyl. itaconate in dimethylforniamide and dimethyl sulphoxide. Titration curves obtained with 0.1 M potassium hydroxide in propan-2-01, 0.1 M potassium t-butoxide in 2-methylpropan-2-01 and 0.1 M n-butyllithium in toluene as titrants are shown in Fig. 5. In Table 11, a range of monobasic organic acids that have been titrated with 0.1 M tetra-n-butylammonium hydroxide solution is listed. Most of the acids examined combineFebruary, 19731 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART 11 96: with the titrant in a 1 : 1 molar ratio, but 2,6-di-t-butyl-4-methylphenol, succinimide and phthalimide react sub-stoicheiometrically while 2-hydroxyquinoline is unreactive.The low values obtained with the first three of these four compounds would appear to result partly from steric hindrance as all of them react to a greater extent, but still not stoicheiometrically, with potassium hydroxide. An explanation for the non-reactivity of 2-hydroxyquinoline would lie in the strong hydrogen bonding of the hydroxyl group with the nitrogen atom. As was noted in Part l , 3 the titration process involves competition between monomer and organic acid for the titrant. Apparently acrylonitrile, succinimide, phthalimide and, possibly, 2,6-di-t-butyl-4-methylphenol have similar reactivities with respect to the titrant.T i t r a n t h l (1 division = 1 ml) Fig. 5. Catalytic thermometric titration with different monomer and titrant - catalyst combinations. a b c d e f g Titrant . . .. K KB B K B L L Monomer/ml .. A,10 A,15 M,2 M,2 T,2 T,l T , l Solvent/ml . . - - F,2 S,2 F,2 F,1 S,1 Compound/mg . . 2,12 X,4 Y,15 R,11 Y,15 2,12 H,9 Titrants (0.1 M)-K, KOH in propan-2-01; KB, potassium t-butoxide in 2-methylpropan-2-01; B, tetra-n-butylammonium hydroxide in toluene - methanol; and L, n-butyllithium in toluene. Monomers-A, acrylonitrile; M, methyl acrylate; and T, di- methyl itaconate. Solvents-F, dimethylformamide ; and S, dimethyl sulphoxide. Compounds-2, benzoic acid ; X, 3,S-xylenol; Y, salicylic acid ; R, resorcinol ; and H, 3,4-dihydroxybenzoic acid A number of polyfunctional acids have been titrated with 0.1 M tetra-n-butylammonium hydroxide and 0.1 M potassium hydroxide solutions in conjunction with acrylonitrile as end-point indicator.In Table 111, the titration values are compared with those obtained by the acetone method of Vaughan and Swithenbank.l It can be seen that with their method the second acidic group in hydroquinone and salicylic acid is determined while with the polymerisation technique it is not. Further, with the potassium hydroxide titrant the second acidic group in resorcinol and pyrogallol is determined while with the tetra-n-butylam- monium hydroxide titrant it is not. The first and second acidic groups in cyanuric acid and the first two and third acidic groups in trithiocyanuric acid can be distinguished in a similar way.With tannic acid, twenty, twelve and ten acidic groups are determined by using the acetone procedure, the polymerisation method with potassium hydroxide titrant and the polymerisation method with tetra-n-butylammonium hydroxide titrant, respectively. The above results with polyfunctional acids suggest that catalytic thermometric titration96 GREENHOW AND SPENCER : IONIC POLYMERISATION FOR END-POINT [Analyst, Vol. 98 TABLE I1 MONOFUNCTIONAL ORGANIC ACIDS TITRATED THERMOMETRICALLY WITH 0.1 M TETRA-n-BUTYLAMMONIUM HYDROXIDE SOLUTION WITH ACRYLONITRILE AS THE END-POINT INDICATOR Conditions: Add 0.1 mequiv of the acid in 1 ml of toluene or dimethylformamide to 10 ml of acrylonitrile in a 50-ml beaker and titrate by using Method A Phenylacetic acid, benzilic acid, hippuric acid and cinnamic acid Benzoic acid, 9-toluic acid, o-nitrobenzoic acid, 3,5-dinitrobenzoic acid, P-aminobenzoic acid, m-aminobenzoic acid, p-methoxybenzoic acid and acetylsalicylic acid 3,5-Xylenol, 2,6-xylenol, 2,6-di-t-butyl-4-methylphenol (0.6) , * o-nitrophenol, o-aminophenol, salicylaldehyde, methyl salicylate and 3-hydroxypyridine 1-Naphthol, l-amino-7-naphthol, 8-hydroxyquinoline and 2-hydroxyquinoline (0) Dirnedone Succinimide (0.17) * and phthalimide (0.35) * titration, the figure being the fraction of the acid function titrated a t the end-point.and 0.89, respectively, with 0.1 M potassium hydroxide in propanol-2-01 as the titrant. Figures in parentheses following the names of compounds indicate non-stoicheiometric * The values for 2,6-di-t-butyl-4-methylphenol, succinimide and phthalimide are 0.73, 0.69 can be made selective by using different titrant - catalysts and different monomers (including acetone).Although acids, or acidic groups within a compound, that are distinguishable by the three methods cannot be classified into groups in a simple manner according to their pK, values, i.e., their acid-dissociation constants in aqueous solution, it is apparent from the pK, values given in Table I11 that the methods are selective within the pK, range 10 to 12 for most of the compounds examined. The anomalous result obtained with succinic acid, which is titrated as a monobasic acid in the acetone method and as a dibasic acid by the polymerisation technique, may be caused by 1 : 1 condensation of the acid with acetone, which would eliminate one carboxyl group. With dichloroisocyanuric acid, a source of “active” chlorine, two equivalents of titrant are consumed in the displacement of the chlorine atoms.TABLE I11 THERMOMETRIC TITRATION OF POLYFUNCTIONAL ORGANIC ACIDS WITH ACRYLONITRILE AND ACETONE AS END-POINT INDICATORS Compound Succinic acid . . .. Resorcinol . . . , . . Pyrocatechol . . .. Hydroquinone . . .. Phloroglucinol . . .. Pyrogallol . . .. . . Salicylic acid . . .. p-Hydroxybenzoic acid . . 3,4-Dihydroxybenzoic acid 3,4,6-Trihydroxybenzoic acid Tannic acid .. .. 2,6-Pyridinedicarboxylic acid Trithiocyanuric acid . . Dichloroisocyanuric acid . . Cyanuric acid . . .. .. . . .. .. .. .. .. .. .. .. .. . . . . .. . . Acidic groups 2 2 2 2 3 3 2 2 3 4 2 3 3 - 1 (3) Groups titrated by method* - P1 P2 K 2 2 (1) 1 1 (1) 1 2 (2) 1 2 (2) 1 1 (22) 1 1 (22) 2 2 2 2 2 2 2 2 2 2 10 12 20 2 2 1.74 1 1 2 2 3 3 2 3 2 pK, valuest -7 PKI PK2 4.21 5-64 9.85 12.08 9.81 11.32 10.85 11.39 8-40 8.88 9.01 11.64 2.98 12-38 4.68 9.3 4-34 8.85 - - - - - - 6-6 10.6 4-90 8-O$ - c * P1: acrylonitrile end-point indicator with tetra-n-butylammonium hydroxide titrant (0.1 M).P2 : acrylonitrile end-point indicator with potassium hydroxide titrant (0.1 M) . K: acetone method with potassium hydroxide titrant (1.0 M) ; values in parentheses are from reference 1. Data are from reference 7, except for t Acid-dissociation constants in aqueous solution. thiocyanuric acid (Mr. J. Chudy, Chelsea College). $ pK, 10.8.February, 19731 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART 11 97 It can be concluded that the polymerisation technique offers a higher degree of sensitivity than has been achieved previously in the non-aqueous titration of organic acids and, in conjunction with the acetone procedure, enables one to obtain selectivity in the study of weaker acids. The sharpness and magnitude of the temperature changes at the end-point when 0.001 M titrant is used suggests the possibility of carrying out determinations in the sub-microgram region with 0.O001 M and weaker titrants. A limitation to the use of weaker titrants is the requirement for a catalyst concentration sufficient to initiate anionic poly- merisation, which automatically limits the final total volume of sample, monomer and titrant at the end-point. REFERENCES 1 . 2. Vaughan, G. A., and Swithenbank, J. J., Analyst, 1966, 90, 694. Vajgand, V. J., Gail, F. F., Zarnic, Lj., Brusin, S., and Velimirovic, D., in Ruzas, I., Editor, “Proceedings of the IIIrd Analytical Chemical Conference,” Volume 2, AkadCmiai Kiad6, Budapest, 1970, p. 443. Greenhow, E. J., and Spencer, L. E., Analyst, 1973, 98, 81. Greenhow, E. J., Chem. & Ind., 1972, 422. - , Ibid., 1972, 466. Vaughan, G. A., and Swithenbank, J. J., Analyst, 1970, 95, 890. Kortum, G., Vogel, W., Andrussow, K. , Editors, “Dissociation Constants of Organic Acids in Aqueous Solution,” International Union of Pure and Applied Chemistry, Butterworths, London, 1961. NOTE-Reference 3 is to Part I of this series. 3. 4. 5 . 6 . 7 . Received June 28th, 1972 Accepted September 28th, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800090

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

98 Artalyst, February, 1973, Vol. 98, pp. 98-102 Ionic Polymerisation as a Means of End-point Indication in Non-aqueous Thermometric Titrimetry Part III.* The Determination of Alkaloids and Alkaloidal Salts BY E. J. GREENHOW AND L. E. SPENCER (Defiartment of Chemistry, Chelsea College, University of London, Manresa Road, London, S. W.3) Strychnine, nicotine, atropine, quinine, papaverine, caffeine and theo- phylline have been determined in amounts down to 0.0001 mequiv, e.g., 33 pg of strychnine and 8.5 pg of nicotine, by catalytic thermometric titration. The hydrochlorides of quinine and ephedrine, ephedrine sulphate, codeine phosphate and atropine methonitrate have been determined by direct titra- tion by using the same technique. Addition of mercury(I1) acetate was not necessary in the titration of the hydrochlorides.Titrations were carried out in non-aqueous solution with 0.1, 0.01 and 0.001 M perchloric acid, with the ionic polymerisation of a-methylstyrene to indicate the end-point. Depending on sample size and the procedure adopted, each determination can be carried out in 2 to 6 minutes by using a manual method, with a thermometer for temperature measurement, or a simple automatic apparatus. The method would appear to be suitable for the determination of alkaloids and related basic compounds that have been extracted from crude drugs, formulations or natural materials with non-basic organic solvents. For most of the determinations it is not necessary to dry wet chloroform extracts before titration. IN Part I1 methods are described for the thermometric titration of organic bases by using ionic polymerisation to indicate the end-point.The organic bases examined were mainly simple derivatives of pyridine and aniline, although some polyfunctional heterocyclic com- pounds, such as benzimidazole, were titrated. It was shown that bases could be determined in amounts down to about 10 pg, depending on the equivalent mass of the base. Apart from the use of this technique in pollution studies, there is no widespread industrial analytical requirement for determinations of simple organic bases a t the 10-pg level. However, in the examination of many natural products and pharmaceutical preparations the determination of small amounts of organic bases is of considerable importance. The determination of alkaloids at the milligram level is a routine procedure in pharmaceutical analysis and forensic investigations.A standard procedure for the assay of alkaloids in crude drugs, galenicals, injections and tablets, which is prescribed in official publications of pharmaceutical organisations, involves solvent extraction of the alkaloid followed by its determination by a gravimetric, titrimetric or spectrophotometric method.2 Gravimetric methods are usually tedious and not necessarily accurate, while spectrophotometric methods, although more sensitive than titrimetric methods, require more careful calibration and more elaborate instrumentation than the latter. In some methods of assay use is made of direct non-aqueous titration with perchloric acid for the determination of the extracted alkaloid, although it is more usual to add an excess of standard acid to the extract and back-titrate in aqueous solution.Alkaloid hydro- chlorides dissolved in organic solvents can be titrated directly with perchloric acid but it is necessary to add mercury(I1) acetate to the sample to complex the chloride ions, which otherwise interfere with the titration. Recommended titrant concentrations are 0.1, 0.05 and 0.025 M for the perchloric acid and 0.1 and 0.02 M for the sodium hydroxide solution used in the back-titration, thus from 0.02 to 0.1 mequiv of sample can be treated with 1 ml of titrant, e.g., 33.4 to 6.7 mg of strychnine. Vajgand and co-workers3-6 have shown that tertiary amines, including caffeine, cinchonine and brucine, can be determined in amounts down to about 2 mg by thermometric titration by using the perchloric acid catalysed reaction between water and acetic acid to indicate the end-point , * For Parts I and I1 of this series, see pp.81 and 90, respectively. 0 SAC and the authors.GREENHOW AND SPENCER 99 In this paper the procedures described in Part I1 have been applied to the determination of some representative alkaloids, purine bases and alkaloidal salts. The aim has been to determine the lower limit of sample size at which reproducible results can be obtained, and to study the application of the method to alkaloidal salts and to extracts obtained by standard separation procedures that are used in assays for alkaloid content. EXPERIMENTAL REAGENTS- Toluene and 1,4-dioxan were AnalaR grade, and lJ2-dichloroethane and nitroethane were laboratory-reagent grade materials.All four solvents were dried over molecular sieve 4A before use. Chloroform (AnalaR grade) was extracted with distilled water so as to remove the ethanol and was used in the wet state or, when required, after drying over molecular sieve 4A. Other solvents, a-methylstyrene, alkaloids, purine bases and alkaloidal salts were labdratory-reagent grade materials and were used as received. Perchloric acid, 0.1 M solution in acetic acid-Prepare this solution and standardise it by the method described in Part 1.l Prepare 0.01 and 0.001 M solutions by diluting the 0.1 M titrant with lJ2-dichloroethane. APPARATUS- A. Manual method-Use a -5 to +50 “C thermometer, graduated in 0.1 “C, the “closed” flask (5 or 15 ml) described in Part II,s a 5-ml burette, graduated in 0.01 ml with the tip drawn out to a capillary about 1 inch long, and a magnetic stirrer.C.* Automatic method-The motor-driven micrometer syringe , 5-ml titration vessel and thermistor are shown diagrammatically in Fig. 1. The motor, a 12 r.p.m. Smith’s Clocks motor, drives at two speeds, 24 and 2.4 r.p.m., through a gear box, and the syringe mounting [Burkard Scientific (Sales) Ltd.] can accommodate 10, 5, 2 and l-ml glass syringes, which gives the choice of eight rates of titrant addition. To bridge circuit and 50-mV recorder \ D B A C Fig. 1. Apparatus for thermometric titrimetry : A, synchronous motor (12 r,p.m.); B, gear box; C, gear change (24 r.p.m.; disengaged; 2-4 r.p.m.); D, micrometer syringe; E, thermistor, 2 kfi; F, insulation; and G, titration flask PROCEDURE A.MANUAL METHOD- Prepare a solution of the base in a suitable solvent, e.g., acetic acid (dry), 1,4-dioxan nitroethane, lJ2-dichloroethane or chloroform. Suitable concentrations are 100, 10 and 1 mequiv 1-1 with 0.1, 0.01 and 0.001 M titrants, respectively. Add 0.1 to 1.0 ml of sample solution to 1 ml of a-methylstyrene in the 5-ml titration flask with a grade A l-ml pipette or an Agla micrometer syringe, add titrant at the rate of 0-4mlmin-1 to within 0.3 ml of the end-point, noting the temperature at 16-s intervals, and complete the titration with addition of titrant at a rate not exceeding 0.2 mlmin-l. Titrate larger sample volumes (up to 3 ml) in the 15-ml flask and use 2 ml of a-methylstyrene.* A semi-automatic method, B, is described in Part I, but was not used in the present investigations.100 GREENHOW AND SPENCER : IONIC POLYMERISATION FOR END-POINT [ArtdySt, VOl. 98 C. AUTOMATIC METHOD- Use the same volumes of sample solution and a-methylstyrene as in the manual procedure but add titrant at a constant rate (not greater than 0.2 ml min-l) and record the temperature on a 50-mV recorder at a chart speed of 600 mm h-1. End-points are measured as in Part I at the “upturn” temperature [method (i)] or at the intersection point of the tangents to the two component parts of the titration curve [method (ii)]. Use of method (i) is preferred when the upturn temperature can be located unambiguously as it gives a titration value corresponding closely to that obtained by potentiometric titration.RESULTS AND DISCUSSION The results obtained from a series of titrations in which standard solutions of the alkaloids and purine bases were titrated with 0.1, 0.01 and 0.001 M perchloric acid, the amount of sample taken being chosen so as to give titres in the range 0.1 to 1.0m1, are summarised in Table I. In all instances it was found that the sample size and titre were linearly related, except in the region close to zero sample size when the 0.001 M titrant was used. In the 0.1 to 1.0-ml range it is possible to determine 0-01 to 0.1 mequiv of alkaloid with 0.1 M titrant, 0.0001 to 0.001 mequiv of alkaloid with 0.001 M titrant and intermediate amounts with titrants of intermediate molarity.Calibration graphs for nicotine, which are similar to those for the other alkaloids, are shown in Fig. 2. TABLE I THERMOMETRIC TITRATION OF ALKALOIDS WITH PERCHLORIC ACID : RANGES OF SAMPLE SIZE SHOWING LINEAR CORRELATION WITH TITRANT VOLUME Samples sizes in milligrams Perchloric acid titrant Alkaloid 0:1 M 0.01 M 0.00 i M Atropine .. . . 29.0-2.9 2’9-0.29 ’ 0.29-0.029 Nicotine . . .. . . 8-6-0.86 0.86-0.0 85 0.085-0.0085 Papaverine . . 6 . 17.0-3.4 3.4-0.34 0.34-0-034 Quinine . . .. . . 384-1.9 1-9-0.19 0*19-0*0 19 Strychnine . . . . 33-3-3.3 3.3-0.33 0.3 3-0.0 3 3 Caffeine . . .. . . 19-4-1.9 1.9-0.19 0.19-0.019 Theophylline . . . . 19.7-2.0 2-0-0.2 0-2-0.02 The manual method (A) was used for the 0.1 M titrations and the automatic method (C) for the 0.01 and 0.001 M titrations.The precision of the thermometric titration method was assessed in Table I, Part I,1 and shown to be of the order of 1.5 per cent., and is marginally better with semi-automatic and automatic methods than when the manual procedure was used. Results obtained with the alkaloids indicate the same order of precision (Table 11). The lower limit of 0.1 ml of titrant was chosen as being a reasonably reproducible titrant volume when the manual procedure is used. Typical titration curves obtained with this procedure are shown in Fig. 2, Part I; titration curves obtained with the automatic method are shown in Fig. 3 in this paper. With the automatic method, total titrant volumes of 0.01 ml can be measured, with a slow rate of titrant addition to give a measurable chart length, but the precision is lower than that which can be obtained with volumes in the 0.1 to 1.0-ml range.With the exception of atropine, the alkaloids gave perchlorates that were insoluble in the titration mixture, and with strychnine and papaverine the precipitates were voluminous. With papaverine the precipitate gave rise to high titration values at the 0.1 mequiv level, owing to occlusion of titrant in the precipitate, and it is recommended that with 0.1 M titrant, the determination of papaverine should be restricted to the 0.05 to 0.01 mequiv range. No special precautions are necessary with 0.1 and 0.01 M titrants but 0-001 M perchloric acid is sensitive to moisture present in the atmosphere; it should be freshly prepared before use and the titration should be carried out in a dry atmosphere.February, 19731 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY.PART 111 101 a b c 1 .o - 0.5 - I 110.0 0.1 F .; \ C .- .I- 0.05 Perchloric acid/ml (1 division = 1 ml) Fig. 2. Calibration graphs for the thermometric titration of nicotine, Titvant- a b C Molarity . . .. . . 0.1 0.01 0.001 Rate of additionlml min-’ 0.2 0-2 0.2 Method . . .. . . A C C Titvation- End-point . . .. . . (2i) (f’ (22) a-hlethylstyrene/ml . . 1 Dry acetic acid is a convenient solvent for most of the alkaloids, alkaloid hydrochlorides and purine bases; quinine was soluble with difficulty in this solvent but could be dissolved in dioxan. Nicotine was titrated in solution in 1,2-dichloroethane. With the exception of nicotine and quinine, which were titrated as diacidic bases, all the compounds examined reacted with perchloric acid stoicheiometrically in a 1 : 1 ratio.The analysis of alkaloidal extracts was simulated by dissolving the alkaloid in chloroform that was saturated with water. With the 0.1 and 0.01 M titrants the solution could be titrated satisfactorily without drying it, but it is essential that water droplets are removed as these completely inhibit the’ cationic polymerisation. With 0.001 M titrants it is advisable to dry all sample solutions. It was found that solutions of the quinine and ephedrine hydrochlorides in dry acetic acid could be titrated directly with perchloric acid without adding mercury(I1) acetate so as TABLE I1 RESULTS FOR PRECISION FROM THE THERMOMETRIC TITRATION OF ALKALOIDS WITH 0.1 TO 0.001 M SOLUTIONS OF PERCHLORIC ACID Titration? * Amount Titrant End- Alkaloid taken/mg molarity* Method point Theophylline .. 9-8 0.1 B (4 Nicotine . . . . 0.85 0.0 1 B (4 Nicotine . . . . 0.085 0.001 B (i) Strychnine . . 0.33 0.001 B (4 hydrochloride . . 18.0 0.1 A (i) Nicotine . . . . 0.086 0.001 B (ii) Quinine Mean titre/ nS ml 3 0.52 4 1.12 3 1.10 3 1-27 3 1.06 3 0.90 Standard deviation 0.010 0.008 0-0 17 0.008 0.006 0.01 1 Coefficient of variation, per cent. r S i n g l e n points value 1.93 1.12 0.71 0.36 1-57 0.91 0.64 0.37 0.54 0.31 1-21 0.70 * Nominal. t See Experimental. Number of titrations.102 GREENHOW AND SPENCER to complex chloride ions. Hydrogen chloride is not a catalyst for cationic polymerisation and does not, therefore, affect end-point sharpness.When mercury(I1) acetate was added to the titration solution a very high titre was obtained with perchloric acid and its value depended on the amount of mercury(I1) acetate added, suggesting that reaction occurs between the titrant and the mercury(I1) acetate either directly or, more probably, by way of an or-methylstyrene - mercury(I1) acetate adduct. I I I Perchloric acid/ml (1 division = 1 rnl) I Fig. 3. Thermometric titration curves obtained by the automatic method. Titvant- a b C Molarity . . .. .. 0.1 0.01 0.001 Rate of additionlml min-l 0.2 0.2 0.2 or-Methylstyrene/ml . . .. 2 2 1 Compound/mg . . . . Atropine, 29.0 Theophylline, 0.98 Nicotine, 0.086 Arrow indicates theoretical end-point (allowing for blank titration) The titration of other alkaloidal salts was investigated with 0.1 M perchloric acid.Ephedrine sulphate in dry acetic acid solution gave slightly low, although reproducible, titra- tion values, and it is possible that sulphuric acid liberated in the titration has a slow catalytic action on the a-methylstyrene. Very low titration values were obtained with atropine methonitrate dissolved in dry acetic acid, suggesting that the latter in some way causes de- composition of the alkaloid. A solution of the methonitrate in a mixture of acetonitrile, dioxan and chloroform (5 + 1 + 1) gave a satisfactory titration. Codeine phosphate is not easily soluble in the usual organic solvents but can be dissolved in a mixture of phenol and chloro- form (1 + l).’ However, when such a solution was titrated there was a large “background” rise in temperature, which made the end-point indistinct and, consequently, the precision poor.A dilute solution of codeine phosphate in dry acetic acid (0.01 mequiv ml-1) gave a satisfactory titration curve and reproducible results. It can be concluded that the thermometric method involving cationic polymerisation to indicate the end-point is suitable for the determination of alkaloids and alkaloid hydro- chlorides at a lower level than has previously been practicable by titrimetric methods. With the automatic apparatus about 10 pg of alkaloid can be determined with 0.001 M titrant. With this titrant, end-point sharpness is such as to suggest that even weaker titrants should be effective and, by taking extreme care to avoid contamination from the atmosphere and using well insulated automatic equipment, determinations at the sub-microgram level might well be possible. Messrs. G. P. Davis and S. F. George are thanked for construction of apparatus. REFERENCES 1. 2. 3. 4. 5. 6. 7. Greenhow, E. J . , and Spencer, L. E., Analyst, 1973, 98, 81. Beckett, A. H., and Stenlake, J. B., “Practical Pharmaceutical Chemistry,” University of London, Vajgand, V. J., and GaLl, F. F., Talanta. 1967, 14, 346. Vajgand, V. J., Kiss, T. A., Ga61, F. F., and Zsigrai, I. J., Ibid., 1968, 15, 699. Vajgand, V. J . , Ga&l, F. F., and Brunn, S. S., Ibid., 1970, 17, 416. Greenhow, E. J . , and Spencer, L. E., Analyst, 1973, 98, 90. Pernarowski, M., Chatten, L., and Levi, L., J. Amer. Pharm. Ass., Sci. Edn, 1964, 43, 746. NOTE-References 1 and 6 are to Parts I and I1 of this series, respectively. The Athlone Press, London, 1962. Received July 13th, 1972 Accepted September 26th, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800098

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, February, 1973, Vol. 98,PP. 103-106 103 Determination of Nitro and Nitroso Compounds by Thermometric Titrimetry BY L. S. BARK AND P. BATE (Department of Chemistry and Applied Chemistry, University of Salford, Salford, Lancashire, M6 4WT) Some nitro and nitroso compounds have been determined by reduction with a known and excess amount of titanium(II1) chloride solution and subsequent thermometric titration of the excess of the titanium(II1) with an iron(II1) solution. The accuracy is f 1 per cent. for 0.4 mequiv of sample and the time taken for a single titration is less than 2 minutes. The over-all time taken for a single determination is about 20 minutes. THE various methods that have been proposed for the determination of nitro and nitroso compounds have been reviewed by Ashworth.lS2 In many of these methods, metal ions are used to reduce the functional group; titanium(II1) appears to have been the most widely used of these ions and tin(I1) and chromium(II1) have been used to a lesser extent. Titan- ium(II1) is preferred to tin(I1) because of the stronger reducing power of the former and the fact that the reductions carried out with its use are generally much more rapides The first method in which titanium(II1) chloride was used for determining nitro com- pounds was reported by Knecht4 in 1903. The method involved the addition of a 100 to 200 per cent.excess of the titanium(II1) reagent to the sample and boiling of the solution for 5 minutes while a stream of carbon dioxide was passed through the solution so as to prevent oxidation of the unreacted titanium(II1) solution.The unreacted titanium(II1) was then titrated with a standard solution of ammonium iron(II1) sulphate. Most of the early methods involved the heating of the reaction mixture in a strongly acidic medium, In some instances, chlorination of the nucleus occurred at the high temperatures that were used. However, Kolthoff and Robinson5 found that in most instances reduction could be carried out at room temperature within a few minutes if a buffer such as sodium citrate was used. Ma and Earleye,' used sodium acetate in preference to sodium citrate because of the higher pH and lower blank readings obtained with sodium acetate, and determined a variety of nitrogen compounds that contained reducible groups. Tiwari and Sharma8s9 preferred to use titanium(II1) sulphate instead of the previously used titanium(II1) chloride, and determined several nitro compounds in the presence and absence of a buffer.In most instances the excess of titanium(II1) reagent has been determined by using ammonium iron(II1) sulphate with thiocyanate as indicator, although other reagents, such as methylene blue, Crystal scarlet and Acid green, have also been used. In all these methods a visual indication of the end-point is used. This method of end-point determination is not always satisfactory, especially when highly coloured samples are involved. The advantages of thermometric titrations over visual titrations have been discussed previously,1° especially for industrial materials and highly coloured samples.However, up to the present time, no methods have been reported in which a thermometric indication of the end-point is used for the determination of the excess of titanium(II1) reagent in the determination of nitro and nitroso compounds. Such a method is reported in this paper. EXPERIMENTAL APPARATUS- Electrical circz4it-This has been described previously10 and is a simple Wheatstone bridge incorporating a thermistor sensor as one of the arms of the bridge. Delivery b.ure#es-The titrant was delivered from a multiroller peristaltic pump (LKB Perspex Pump 10200), delivering 0.3 to 0.4 ml min-l. The delivery rate was monitored by gravimet ry . The titanium( 111) chloride solution was dispensed from a Radiometer Autoburette ABUll with a 25-ml burette so that a known volume of solution could be added accurately.0 SAC and the authors,104 [Analyst, Vol. 98 Nitrogen Puuri$cation train-The nitrogen was passed from a cylinder through two Drechsel bottles, the first containing a reagent to remove oxygen and the second distilled water, into the reaction vessel. An alkaline solution of pyrogallol was tried in the first bottle, but it became spent after only a few days. A solution of chromium(I1) chloride was therefore used, which was found to be much more efficient as the reagent was still useful after 3 months. Reaction $ask-A three-necked, pear-shaped flask of 25 ml capacity was used; one of the necks contained the thermistor, another the burette tip and the centre neck a glass tube drawn out into a capillary through which the nitrogen passed into the solution.The reaction flask was surrounded with a block of expanded polystyrene, which was built around a Metrohm magnetic stirrer. The top part of the flask was covered with layers of cotton-wool so that the whole flask was insulated from its surroundings. The solution was stirred magnetically at a constant rate with a polythene-covered stirring bar in a conventional manner. PRELIMINARY INVESTIGATIONS- A study was made of the reaction conditions that influence the shape of the enthalpo- grams obtained when titanium(II1) solutions were titrated with iron(II1) ions [from am- monium iron(II1) sulphate]. Studies were made of solvent effects and the effects of variations in the acidity of the system. SoZvent efects-In many instances an organic solvent has to be used to dissolve the nitro or nitroso compound.It is advantageous to use a solvent that is completely miscible with the aqueous solutions that are subsequently used. Hence only ethanol, acetone and glacial acetic acid were investigated, each of which showed different thermal effects when diluted with solutions of ammonium iron(II1) sulphate during the titration of the excess of the titanium(II1) ions. The heats of dilution and mixing of the titrant solution with the aqueous organic solution of the titrand, together with the heat of reaction of the titanium(II1) and the iron(II1) ions, determine the shape of the enthalpogram produced. This shape may affect the accuracy with which the end-point can be determined. Enthalpograms were obtained by using the three solvents under identical conditions : aliquots of the solvent (5 ml) under investigation were used, and also of the titanium(II1) chloride solution (5 ml of 0.08 M solution), sodium acetate solution (7 ml of 2.5 M solution) and hydrochloric acid (1 ml of 50 per cent.V/V acid). The graphs obtained with glacial acetic acid and acetone had very rounded end-points and accurate determinations were not possible. All further work was therefore carried out only with ethanol. E$ects of variation in the acidity of the system-It had been found previously6 that titanium(II1) chloride solutions containing less than 10 per cent. V/V of hydrochloric acid BARK AND BATE: DETERMINATION OF NITRO AND NITROSO h 4 b Volume of titrant added Fig. 1. Enthalpograms for titration of titan- ium(II1) solutions under different conditions with 0.8 M ammonium iron(II1) sulphate solutionFebruary, 19731 COMPOUNDS BY THERMOMETRIC TITRIMETRY 105 were readily oxidised when stored in the usual manner.It had also been recommended6 that the acid is added to the sample after reduction of the organic group and before oxidation of the excess of the titanium(II1) ion. Thus enthalpograms were obtained by using different concentrations of hydrochloric acid in the titrand. The concentration of the acid in the titrant was adjusted to 25 per cent. V/V so that at all stages of the titration the titrand was acidic and hence decomposition of the titanium(II1) by oxidation would be minimised. Mixtures of 5 ml of ethanol, 5 ml of 0-08 M titanium(II1) chloride solution, 7 ml of 2.5 M sodium acetate solution and 5 ml of different dilutions of concentrated hydrochloric acid (5 + 0, 4 + 1, 3 + 2, 2 + 3, 1 + 4 and 0 + 5 ) were titrated with 0.8 M ammonium iron(II1) sulphate solution and the enthalpograms obtained are shown schematically in Fig.1. Enthalpogram 1 is characteristic of the solution that contains no added hydrochloric acid, enthalpogram 4 that of solutions that contain 4 ml of 11.5 M hydrochloric acid, while enthalpograms 2 and 3 are characteristic of solutions that have acid concentrations inter- mediate between those for enthalpograms 1 and 4. For each of the enthalpograms, the line BC represents the sum of the heats of reaction between iron(II1) and titanium(II1) and also the heat of dilution and mixing of the titrant acid in the various mixtures.The heat of dilution and mixing is shown by the line CD. In practice, when obtaining an enthalpogram of type 2 by using the 0.16 M titanium(II1) solution prepared from the titanium( 111) chloride solution obtainable commercially, which contains approximately 15 per cent. m/V of titanium(III), it was found that the acid con- centration of the original concentrated solution of titanium(II1) was sufficient to ensure that on dilution to 0.16 M titanium(II1) the diluted solution contained sufficient acid to give type 2 enthalpograms without the addition of further acid. REAGENTS- Titanium(I1I) chloride solution, 0.16 M-Titanium(II1) chloride (76 ml of a 15 per cent. m/V solution) was added to 50 ml of concentrated hydrochloric acid (sp.gr. 1.16) and the mixture diluted to 500 ml with distilled water. This diluted solution was then added to the reservoir of the Autoburette and 1OOg of zinc amalgam were added. The solution was left for 24 hours before use so as to attain a stable and reproducible state. Iron(II1) solution, 0.8 M-Ammonium iron(II1) sulphate (195 g) was dissolved in a mixture of 125 ml of concentrated hydrochloric acid and 300 ml of distilled water. The solu- tion was filtered and the filtrate was made up to 500 ml with distilled water and standardised by an iodimetric method. Zinc amalgam-"Mossy" zinc (100 g) was treated with a solution of mercury(I1) chloride (10 g of HgC1, dissolved in a mixture of 5 ml of concentrated hydrochloric acid and 150 ml of water).After 5 minutes, the solution was poured off and the zinc amalgam was washed several times with distilled water. Chromium(I1) chloride solution-This solution was prepared by a previously reported method. l1 Sodium acetate, 2.5 M-Anhydrous sodium acetate (103 g) was dissolved in distilled water and the solution made up to 500 ml. Hydrochloric acid, sp. gr. 1.16. Solvent-E t hanol. Reducible nitrogen compounds-All compounds were purified before use and solutions were made by dissolving an amount of the compound in ethanol such that a 5-ml aliquot of the solution was equivalent to approximately 0.4 molar equivalent of sample. PROPOSED METHOD- A 5-ml aliquot of the nitrogen-containing compound (approximately 0.4 molar equivalent) is transferred by pipette into the reagent flask followed by 7 ml of 2.5 M sodium acetate solution.Nitrogen is passed through the solution for 10 minutes at the rate of 10 to 15 ml min-l while the solution is stirred. After this period, a known amount (approximately 5 ml) of the titanium(II1) chloride solution is added from the Autoburette. After allowing 5 minutes for reduction of the functional group, 4ml of distilled water are added and the burette tip and thermistor inserted in the solution. The nitrogen flow is stopped as the flow has a cooling effect on the solution (probably owing to the evaporation of the solvent). As the flask is virtually sealed, no oxidation of the titanium(II1) solution apparently occurs in the time taken to carry out the titration (1 minute). It was used immediately.106 BARK AND BATE The solution is then titrated with the ammonium iron(II1) sulphate solution.The amount of unreacted titanium(II1) solution is then determined from the enthalpo- gram and hence the amount of reducible substance originally present can be calculated. The titanium(II1) solution is standardised by taking a similar aliquot of organic solvent without the presence of any reducible nitrogen compound and proceeding as above. The results for various nitro and nitroso compounds are given in Table I. TABLE I RESULTS FOR THE DETERMINATION OF NITRO AND NITROSO COMPOUNDS Compound Amount takenlmg Amount found/mg Purity, per cent. Nitrobenzene . . .. . . .. 6.96 6.97 100.1 8.82 8.81 99.8 1,3-Dinitrobenzene . . .. .. 5-18 5.13 99.0 4.14 4.13 99.8 2,4-Dinitrobenzoic acid .. .. 4.68 4.7 1 100.7 5-80 5.82 100-3 4-Nitrobenzoic acid . . .. . . 8.69 8.70 100.1 6.95 6.93 99.7 4-Nitrophenol .. .. .. 8-46 8.49 100.4 6.77 6.78 100.2 3-Nitrophthalic acid .. ,. 12.56 12-47 99-3 10.04 10.07 100.3 4-Nitroaniline .. .. . . 8.50 8.46 99.5 6-80 6.77 99.6 8-Nitroquinoline . . .. .. 10.22 10.18 99-6 8-18 8-15 99.6 4-Nitroacetanilide . . .. .. 10.03 10.00 99.7 8.02 8.06 100.6 1 -Nitroso-2-naphthol .. . . 11.41 11.35 99.5 14.23 14.39 101.1 2-Nitroso- l-naphthol .. . . 13-24 13-20 99.7 10-56 10.63 100.7 4-Nitroso-NN’-diethylaniline . . 14.23 14.14 99.4 11.38 11-34 99.7 N-Nitrosodiphenylamine . . .. 9.47 9-50 100.4 7-57 7.64 99.6 INTERFERENCES- The most troublesome interference in the method is caused by oxygen, but the steps taken to avoid its presence were adequate for the present work.However, any reducible substance will interfere in the determination although ethylenic and acetylenic groups generally are not reduced by titanium(II1) chloride. Ma and Earley6 reported that nitroso compounds could be determined in the presence of nitro compounds by excluding the buffer and carrying out the reduction in strongly acidic media. However, in the present work it was found that nitro compounds interfered in the nitroso determination even if acidic conditions were used. CONCLUSION Some nitro and nitroso compounds have been determined by their reduction with titanium(II1) chloride solution. The accuracy is &l per cent. for 0-4 molar equivalents of sample. The time taken for a single titration is less than 2 minutes and the over-all time taken for a single determination is about 20 minutes. REFERENCES 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. Ashworth, M. R. F., “Titrimetric Organic Analysis. Part I. Direct Methods,” Interscience Pub- - , “Titrimetric Organic Analysis. Part 11. Indirect Methods,” Interscience Publishers, New Glynn, E., Analyst, 1947, 72, 248. Knecht, E., Bey. dt. chem. Ges., 1903, 36, 166. Kolthoff, I. M., and Robinson, C., Recl Trav. Chim. Puys-Bas Belg., 1926, 45, 169. Ma, T. S., and Earley, J. V., Mikrochim. Acta, 1959, 129. -,- , Ibid., 1960, 685. Tiwari, R. D., and Sharma, J. P., 2. analyt. Chem., 1962, 191, 329. -, -, Analyt. Chem., 1963, 35, 1307. Bark, L. S., and Bate, P., Analyst, 1971, 96, 881. Vogel, A. I., “Quantitative Inorganic Analysis,” Longmans Green and Co. Ltd., London, 1964. lishers, New York, 1964. York, 1966. Received August 31st, 1972 Accepted October 6th, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800103

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, February, 1973, Vol. 98, $9. 107-115 107 Thin-layer Chromatography of Simple Urea - Formaldehyde - Methanol Reaction Products Part I.* Qualitative Aspects BY P. R. LUDLAM (The Borden Chemical Company ( U . K.) Limited, North Baddesley, Southampton, SO6 9ZB) Methods are described for the preparation of addition and condensation products of urea and formaldehyde of low relative molecular mass and their methyl esters. The stability of these compounds both as solids and in solution is discussed. Conditions are described that enable most compounds to be separated adequately by thin-layer chromatography without decomposition or other reaction occurring on the plate. The implications of the colours given by the compounds on a chromatographic plate and the effect of sub- stituents on the RF value are discussed.FOR many years resins manufactured by the condensation of urea and formaldehyde under various conditions and over a range of molecular ratios have held a position of considerable importance in the adhesive, textile finishing and moulded plastics fields. Many commercial urea - formaldehyde resins contain only moderate amounts of material with a relative molecular mass of less than 200. Because of the large number and extreme complexity of compounds of high relative molecular mass, this work was mainly directed towards the chromatographic separation of compounds with relative molecular masses below about 200. Methanol is nearly always present in commercial formaldehyde, either in small amounts, as a result of incomplete oxidation during manufacture, or at the 2 to 10 per cent.level, when it is added in order to improve the stability of the solution. If, during the preparation of urea - formaldehyde condensation products the reaction mixture is made even mildly acidic, there will be a tendency for any methanol present to undergo etherification reactions with methylol (hydroxymethyl) groups present. Occasionally substantial amounts of methanol are added to reaction mixtures with the intention of forming ethers and consequently modify- ing the properties of the final resin. Thus, as methyl ethers are to be expected in resins, and for analytical considerations that will be discussed in detail in Part I1 of this paper, the methyl ethers of the methylol compounds have been prepared and studied by thin-layer chromatography.Chromatographic studies of urea - formaldehyde - methanol condensation products of low relative molecular mass have been made by Hamadal and Inoue and Kawai2 on paper in one dimension. The poor separation of urea, monomethylolurea and dimethylolurea severely limits the information that can be obtained on commercial products. It03-5 carried out two-dimensional chromatography on paper with methanol in one direction and pyridine - chloroform - water (17 + 8 + 3) in the second dimension. Good separation was obtained and a careful examination of resinous condensates was undertaken. No reference can be found to chromatography on thin layers or to any quantitative aspects of chromatography in this field. A major consideration in the chemistry and chromatographic separation of urea - formaldehyde - methanol compounds is their instability. In general, they are reactive materials ; they will polymerise, disproportionate or decompose readily.A few important generalisations can be made : (i) Methylenediurea is stable in the solid form. It will, however, hydrolyse in aqueous solution, the reaction being catalysed by hydrogen ionss (ii) The ethers are more stable, both in solution and as solids, than the methylol com- pounds and can be stored for many months at room temperature without marked decom- position. * For Part I1 of this series, see p. 116. 0 SAC and the author.108 LUDLAM : THIN-LAYER CHROMATOGRAPHY OF SIMPLE [ArtabSt, Vol. 98 (iii) The methylol compounds, even if prepared in a pure state and stored at normal temperatures, show indications of decomposition after a few weeks and, in aqueous or alcoholic solution, can show some indication of decomposition or reaction after a few hours.(iv) The reactions of methylol compounds and, to a lesser extent, the ethers, are catalysed strongly by hydrogen ions. Therefore, if their solutions are applied directly to chromato- graphic plates of an acidic nature, decomposition will occur. This problem can be overcome by pre-treating the plates with ammonia vapour immediately before application of the solutions. The simplest compounds that can be formed from urea and formaldehyde under alkaline conditions are monomethylolurea, I, and dimethylolurea, 11. These compounds can easily H2N-CO-NH-CH2-OH HO-CH2-NH-CO-NH-CH2-OH I I1 I11 IV CHa-O-CH2-NH-CO-NH-CH2-OH H2N-CO-NH-CH2-NH-CO-NH2 V VI H2N-CO-NH-CH2-O-CHS CHS-O-CHZ-NH-CO-NH-CH2-O-CH 3 be converted into their methyl ethers, i.e., monomethylolurea monomethyl ether, 111, and dimethylolurea dimethyl ether, IV.Dimethylolurea monomethyl ether, V, can also be prepared. These five simple compounds of urea, formaldehyde and methanol have all been prepared in a chromatographically pure condition. By causing formaldehyde to react with excess of urea under acidic conditions methylenediurea, VI, can be prepared in a pure, crystal- line condition. This last compound, as with urea, will readily condense with formaldehyde and methanol at the primary amido nitrogen atoms, thus giving a series of compounds analogous to that formed by urea.All of these methylol compounds and their ethers have been prepared but all contain contaminants to a lesser or greater extent. However, by comparing their chromatographic behaviour with that of the urea derivatives, an unambiguous identification can be made on the chromatographic plate. If, during the preparation of methylenediurea from urea and formaldehyde, the urea is not present in a large enough excess, considerable contamination of the product with di- methylenetriurea will result. This substance has not been obtained in a pure form but it can be identified on the chromatographic plate. SYNTHESIS OF COMPOUNDS FOR CHROMATOGRAPHY All of the compounds discussed above can be obtained from urea, formaldehyde and methanol according to the processes illustrated in Fig.1. MONOMETHYLOLUREA- The method used for the synthesis of monomethylolurea is essentially that of Einhorn and Hamburger.' However, the preparation is simplified slightly by using disodium hydrogen orthophosphate instead of barium hydroxide to attain the necessary pH. A two-fold excess of urea prevents contamination of the monomethylolurea with dimethylolurea, which, if formed in any significant amount, is extremely difficult to remove by simple recrystallisation procedures. Dissolve 1 g of disodium hydrogen orthophosphate in 42 g of 36 per cent. aqueous form- aldehyde (methanol up to a limit of 10 per cent. in the formaldehyde will not interfere). To the solution add 60 g of urea and stir the mixture while maintaining the temperature at less than 25 "C by running water round the reaction vessel.When the urea has completely dissolved, after about 2 hours, place the reaction vessel and its contents in a refrigerator at a temperature of 0 "C for 15 to 24 hours, by which time the reaction mixture will have solidified. Break up the mass and form a slurry with about 20 ml of industrial methylated spirit containing 1 per cent. V/V of a 10 per cent. m/V aqueous solution of disodium hydrogen orthophosphate, filter and recrystallise twice from ethanol containing disodium hydrogen orthophosphate as before. Thin-layer chromatography (described below) indicates that the monomethylolurea prepared by this method is free from significant amounts of urea and other urea derivatives. The melting-point (capillary method) was found to be 111 "C.The value given in the literature is 111 "C.7(DMU.MME) 9/, (MMU) U.CH2.0.CH3- HO.CH2.U.CHz.O.CH3 (MMU.MME) 109 (DMU) 3 l5 C H 3 .O .C H 2. U . C H 2 .O G H 3 (DMU.DME) DIMETHYLOLUREA- Dimethylolurea is prepared by the customary method.* Dissolve 1 g of disodium hydrogen orthophosphate in 169 g of 36 per cent. aqueous form- aldehyde and add 60 g of urea. Stir the mixture while maintaining the temperature at less than 25 "C by running water round the reaction vessel. When the exothermic reaction has subsided, after 2 hours, place the reaction vessel and contents in a refrigerator at a temperature of 0 "C for 15 to 24 hours. Filter off the crude product and recrystallise twice from industrial methylated spirit. Thin-layer chromatography shows that the dimethylolurea prepared by this method is free from significant amounts of urea and other urea derivatives.An accurate melting-point (capillary method) cannot be obtained as the decomposition of dimethylolurea commences at temperatures below its melting-point. The melting-point as determined on a hot-plate is 136 "C (with decomposition). Values given in the literature range from 126 "C* to 139 OC.Q METHYLENEDIUREA- KadowakilO described a method for the preparation of methylenediurea but, as prepared by his procedure, it was heavily contaminated with dimethylenetriurea, which it was extremely difficult to remove. However, if the molar ratio of urea to formaldehyde is increased from 4: 1 to 10: 1, pure methylenediurea can easily be prepared, albeit in low yields.The con- siderable urea contaminant is removed quantitatively during recrystallisation. Aqueous formaldehyde (44 per cent.) is used in this method for the preparation of methylenediurea as it is essentially free from methanol and therefore the formation of methyl ethers in the reaction mixture is prevented. It is, however, unlikely that the use of formaldehyde containing up to 6 per cent. of methanol would cause undue problems in the purification of the methylene- diurea. Stir 400 g of urea with 300 ml of water, 21 g of 44 per cent. aqueous formaldehyde and 2 g of phosphoric acid until all the urea has dissolved. After leaving it to stand for 24 hours at room temperature, cool the solution to 0 "C and leave it for a further 24 hours. Filter off the crude methylenediurea and recrystallise it twice from water.110 LUDLAM : THIN-LAYER CHROMATOGRAPHY OF SIMPLE [Analyst, VOl.98 Thin-layer chromatography shows that the methylenediurea is free from urea, dimethyl- enetriurea and other urea condensation products. As with dimethylolurea, decomposition begins to occur below the melting-point but the melting-point on a hot-plate was found to be 208 "C. The value given in the literaturelo is 218 "C. MONOMETHYLOLUREA MONOMETHYL ETHER- The method used for the preparation is that described by Kadowaki.lo Add 4-25g of pure monomethylolurea to 25 ml of methanol containing one drop of 5 N hydrochloric acid and shake or stir the mixture vigorously. The monomethylolurea should dissolve and react within 1 minute. Next, add 0.3 g of finely powdered silver carbonate, continuously shaking the flask to ensure complete and rapid neutralisation of the hydrochloric acid.After 5 minutes, filter the solution and remove the methanol at room temperature by evaporation in a jet of air or in a rotary evaporator. Recrystallise the crude ether twice from ethyl acetate. Thin-layer chromatography shows that the ether is free from significant amounts of impurities such as monomethylolurea or dimethylolurea and its ethers. The melting-point by the capillary method was found to be 91 "C. The value given in the literaturelo is also 91 "C. DIMETHYLOLUREA DIMETHYL ETHER- Kadowaki's method for synthesislo is analogous to that used for monomethylolurea monomethyl ether and was found to be suitable. Add 5 g of pure dimethylolurea to 50 ml of methanol containing one drop of 5 N hydro- chloric acid and shake or stir the mixture vigorously.After 1 minute, when dissolution should be complete, add 0.3g of finely powdered silver carbonate and shake or stir the mixture continuously to ensure complete and rapid neutralisation of the hydrochloric acid. After a further 5 minutes filter the solution and remove the methanol at room temperature, either by evaporation in a jet of air or in a rotary evaporator. Recrystallise the crude ether twice from ethyl acetate. Thin-layer chromatography shows that the ether is free from significant amounts of impurities such as monomethylolurea and dimethylolurea. The melting-point, determined by using the capillary method, was 101 "C.The value given in the literaturelo is 101 "C. DIMETHYLOLUREA MONOMETHYL ETHER- Monomethylolurea monomethyl ether was allowed to react with formaldehyde under slightly alkaline conditions to give a pure, crystalline product. Dissolve 0.1 g of disodium hydrogen orthophosphate in 1 ml of water and add 4.2 g of 36 per cent. aqueous formaldehyde and 5.2 g of monomethylolurea monomethyl ether. Shake the mixture to dissolve the solid material and maintain the temperature at less than 25 "C, by use of running water, for 2 hours. Place the reaction mixture in a refrigerator maintained at 0 "C for 24 hours. Filter off the crystals and dissolve them in 15 ml of ethanol, add 50ml of ethyl acetate and set the solution aside to facilitate crystallisation. Finally, recrystallise twice from 90 + 10 ethyl acetate - ethanol to obtain platelet crystals.Thin- layer chromatography shows that impurities are not present in significant amounts. The melting-point, determined by use of the capillary method, was 98 "C. The value given in the literaturell is 94 to 96 "C. METHYLOLMETHYLENEDIUREAS- By analogy with the preparation of monomethylolurea and dimethylolurea, it should be possible to prepare monomethylolmethylenediurea and dimethylolmethylenediurea by reacting methylenediurea at pH 9 with 1 and 2 mol of formaldehyde, respectively. However, the solubilities of methylenediurea and its methylol derivatives in water are low so that dilute solutions have to be used in the initial condensation procedure, which results in relatively poor yields.Similarly, purification procedures are hampered by the solubility characteristics. If methylenediurea and formaldehyde in a molar ratio of 1 : 1 are made to react together at pH 9 for 24 hours a t room temperature the reaction mixture contains not only mono- methylolmethylenediurea and methylenediurea but also a considerable amount of the di- methylol compound. The incidence of the dimethylol compound can be reduced considerably by using less formaldehyde (e.g., a molar ratio of 1:0-73) but it still proves impossible to remove the dimethylol compound by simple crystallisation procedures.February, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART I 111 In the preparation of dimethylolmethylenediurea , if an excess of formaldehyde were used, the concentration of the monomethylol compound would be expected to be small.This proved to be so, but difficulties were again encountered in the purification of the crude reaction mixture, caused by the excess of formaldehyde remaining in solution, presumably as the hemiacetals of the methylol compounds, and causing a marked tendency for poly- merisation reactions to occur. These preparation difficulties have not been overcome but the following procedures do produce fairly stable solids with the desired compound in the greatest concentration. The impurities present are those which are to be expected and can easily be identified on the chromatographic plate. MONOMETHYLOLMETHYLENEDIUREA- Dissolve 1.3 g (0.01 mol) of methylenediurea in 25 ml of hot water containing 0.1 g of disodium hydrogen orthophosphate.Cool the solution quickly and, before the methylene- diurea crystallises out, add 0.61 g (0-0073 mol) of 36 per cent. aqueous formaldehyde. Stir the solution overnight at room temperature and then evaporate it to dryness at a temperature not exceeding 30 "C, either in a rotary evaporator, or by passing a jet of air over the solution in an evaporating basin. The residue will contain dimethylolmethylenediurea as an impurity and also a considerable amount of methylenediurea. The methylenediurea can be removed by dissolving the crude methylol compound in 30 ml of hot 80 + 20 water - ethanol mixture and cooling quickly. The methylenediurea remains in solution and the methylol compounds precipitate out. The ratio of monomethylolmethylenediurea to dimethylolmethylenediurea is not changed by this procedure.DIMETHYLOLMETHYLENEDIUREA- Dissolve 1.3 g (0.01 mol) of methylenediurea in 25 ml of hot water containing 0.1 g of disodium hydrogen orthophosphate. Cool the solution quickly and, before the methylene- diurea crystallises out, add 1.7 g (0.02 mol) of 36 per cent. aqueous formaldehyde. Stir the solu- tion overnight at room temperature and then evaporate it to dryness at a temperature not exceeding 30 "C, either in a rotary evaporator or by passing a jet of air over the solution in an evaporating basin. The solid thus obtained contains some of the monomethylol compound as an impurity and also some unchanged methylenediurea. The latter compound can be removed by dissolving the solid in 30 ml of hot 80 + 20 water - ethanol and cooling quickly.The ratio of monomethylolmethylenediurea to dimethylolmethylenediurea is not effectively altered by this procedure. MONOMETHYLOLMETHYLENEDIUREA MONOMETHYL ETHER- The impure monomethylolmethylenediurea can easily be converted into the methyl ether by the following procedure. Reduce 1 g of monomethylolmethylenediurea to a fine powder and suspend it in 20 ml of methanol. Add 1 drop of concentrated hydrochloric acid and stir the mixture for 3 minutes, by which time most of the impure methylol compound should have reacted and passed into solution. Add 0.3 g of silver carbonate, grinding the particles with a glass rod against the walls of the vessel to ensure rapid and complete neutralisation of the free acid. Stir the solu- tion for 5 minutes and then filter.Evaporate the filtrate to dryness at room temperature in a rotary evaporator, or, alternatively, by passing a jet of air over the surface of the liquid. The remaining solid is mostly monomethylolmethylenediurea monomethyl ether, but contains a considerable amount of dimethylolmethylenediurea dimethyl ether. DIMETHYLOLMETHYLENEDIUREA DIMETHYL ETHER- The reaction of 1 g of crude dimethylolmethylenediurea with methanol is carried out by a procedure exactly analogous to that described above for the monomethylol compound. The solid resulting from the evaporation of the neutralised methanolic solution is mainly dimethylolmethylenediurea dimethyl ether, but contains some monomethylolmethylenediurea monomethyl ether. DIMETHYLOLMETHYLENEDIUREA MONOMETHYL ETHER- This material, so far obtained only in a very impure form, is made by condensing crude monomethylolmethylenediurea monomethyl ether with an equimolar amount of form-112 LUDLAM: THIN-LAYER CHROMATOGRAPHY OF SIMPLE [AfiaZyst, Vol.98 aldehyde in aqueous solution at pH 9.5. The resulting material contains dimethylolmethylene- diurea dimethyl ether, monomethylolmethylenediurea monomethyl ether and methylenediurea as the principal impurities. Dissolve 0.8 g of crude monomethylolmethylenediurea methyl ether in 1 ml of water containing 0.1 g of disodium hydrogen orthophosphate. Add 0.25 g of 36 per cent. aqueous formaldehyde and allow the solution to stand at room temperature overnight. Filter off the crude dimethylolmethylenediurea monomethyl ether.CHROMATOGRAPHIC DETAILS PLATES- Commercial thin-layer plates of several kinds have been used but none seems to offer any significant advantage over Merck Kieselgel F264 (fast running) spread on glass plates. The plates are not activated before use but are stored over silica gel. Immediately before use, the plate is exposed to ammonia vapour for a few seconds by holding it in the chromato- graphic chamber above the solvent, which contains ammonia. ELUTING SOLVENT- Numerous solvent systems have been investigated, and it was found to be generally true that the presence of ammonia, or some other basic compound, is essential for adequate separation, notably of urea, monomethylolurea and dimethylolurea, to be achieved. Two solvent systems have proved to be satisfactory: ethyl acetate - methanol - ammonia solution (sp.gr. 0.880) (88 + 6 + 6) is used when the emphasis is on the separation and detection of ethers and methylol compounds of urea; and ethyl acetate - methanol - ammonia solution (sp. gr. 0.880) (80 + 15 + 5) when examining mixtures for methylenediurea, the methylol- methylenediureas and dimethylenetriurea. CHROMATOGRAPHIC TANK- ensure that the atmosphere in the tank was saturated with solvent. DETECTION PROCEDURES- Many spray reagents and detection procedures have been examined in the course of this investigation. Some, such as picric acid, ninhydrin, Schiff’s reagent, phenylhydrazine - nickel sulphate, potassium permanganate in dilute sulphuric acid and various concentrations of potassium dichromate in sulphuric acid, were found to be either very insensitive or very specific, e.g., Schiff’s reagent gave colours only with compounds that liberated formaldehyde.Some procedures were partially successful and were used for a time, often until a more suitable method was found. These reagents and procedures include the following. p-Dimethylaminobenzaldehyde in ethanol, 1 per cent. solution-The plate was sprayed with the reagent and placed for 5 minutes in a vessel saturated with hydrogen chloride. This reagent showed good sensitivity to urea and compounds containing primary amido groups but secondary amido compounds were detected only at relatively high concentrations. The contrast between the spots and the background plate (yellow on white) was poor. Dichloropuoresceinn solution - bromine vapour-The plate was slightly moistened by spray- ing it with 0.05 per cent. dichlorofluorescein in 1 N sodium hydroxide solution, exposed to bromine vapour until the initial pink colour was discharged and finally sprayed heavily with the dichlorofluorescein solution.Pink spots were produced on a pale yellow background. This procedure was sensitive but the factors that are involved in colour formation were not easily controlled and reproducibility was found to be poor. Any ammonia or basic materials remaining on the plate also interfered with colour production. The sensitivity was found found to be about 0.2 pg for dimethylolurea. Alkaline potassium pentacyanonitrosylfe rrate(III) (potassium nitroprusside) - potassium hexacyano ferrate(III) solution-Equal volumes of 10 per cent.solutions of potassium penta- cyanonitrosylferrate(III), potassium hydroxide and potassium hexacyanoferrate(II1) were mixed and used immediately, as the mixture is stable for only about half an hour. Purple spots were produced on a brownish yellow background. Two main drawbacks were found with this spray: it was fairly insensitive, as the minimum amount of dimethylolurea that Both solvents must be prepared daily. The tank used in this work measured 22 x 22 x 7 cm. No precautions were taken toFebruary, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART I 113 could be detected was 15 pg; and the colours faded within 5 minutes, making it necessary to photograph the plates in order to allow full interpretation.ADOPTED PROCEDURE- The most widely suitable procedure consists in exposing the plate to chlorine gas and, after allowing sufficient time for the excess of chlorine to disperse, spraying the plate with a solution of an aromatic amine in glacial acetic acid. Of the aromatic amines tested, o-dianisidine is probably the most sensitive, but compared with o-toluidine, which is the amine preferred in this work, it has several disadvantages: the colours of the spots are not so informative as those produced by o-toluidine; even after allowing the chlorine to disperse for several hours, a strong and variable background colour is produced; the storage life of the plate is only a few days a t most, whereas plates sprayed with o-toluidine can be stored for several weeks; and the toxicity of o-dianisidine is probably much greater.SPRAY REAGENT- The spray reagent chosen was a 5 per cent. solution of o-toluidine in glacial acetic acid. The solution is stable for up to 8 weeks, after which the colours of the spots produced by the reagent become less reliable. The chlorine - o-toluidine procedure is capable of detecting approximately 1 pg of sub- stances that give blue spots (urea, methylenediurea, etc.), 3 pg of substances that give green spots (monomethylolurea, etc.) and 5 pg of substances that give yellow spots (dimethylol- urea, etc.). METHOD Prepare 5 per cent. solutions of the reference compounds in methanol when possible. Methylenediurea and its methylol derivatives are almost insoluble in methanol and aqueous solutions should be prepared, by heating to 70 "C if necessary. The hot, aqueous solutions should be spotted on to the plate as quickly as possible so as to prevent excessive reaction.Urea - formaldehyde reaction mixtures are best applied to the plate as solutions of up to 20 per cent. concentration in 1 + 1 methanol - water. Spot 1 pl of each solution on to the ammonia-treated pIate, allow the spots to dry and develop the chromatogram in the solvent mixture of the appropriate proportions for the requirements (see Eluting solvent). Allow the plate to dry at room temperature for 15 minutes after development. (Elevated drying temperatures can cause decomposition of the compounds to take place on the plate, leading to reduced spot intensities and unexpected spot colours.) Next, expose the dry plate to chlorine gas, either in a separate vessel or by directing the gas from a cylinder on to the plate in a fume hood. The uptake of chlorine is rapid and complete chlorination is achieved in a few seconds.Allow the excess of chlorine to disperse from the plate for 5 minutes at room temperature and then spray the plate with the 5 per cent. o-toluidine in acetic acid solution. A preliminary examination of the plate can be made after a few minutes but the full colours take about 8 hours to develop. It is recommended that during this time the plate be kept in the dark. Plates thus prepared are stable for several weeks. RESULTS AND DISCUSSION Idealised separation patterns and R, values of the compounds are shown in Fig. 2. Although a specific method for the preparation of dimethylenetriurea is not given, it can be observed in crude methylenediurea prepared with a molar ratio of urea to formaldehyde of 6: 1 or less, and for this reason its position on the chromatographic plate is shown.Form- aldehyde is often present with the urea derivatives and is chromatographed as hexamine, owing to reaction with the ammonia in the solvent system. The colours given by the various urea derivatives are characteristic of the chemical groupings in the molecule or, to be more specific, the degree of substitution on the amido nitrogen atoms. The primary amido grouping -CO.NH, produces a blue colour, while substituted amido groups, - C O . N H R , where R is either -CH,OH or -CH2.0CH8, give a yellow colour. Thus urea, methylenediurea and dimethylenetriurea give blue spots, while dimethylol compounds and their ethers give yellow spots.The monomethylol derivatives of urea and methylenediurea, together with their ethers, contain one grouping that is associated with a blue114 LUDLAM : THIN-LAYER CHROMATOGRAPHY OF SIMPLE [AfidySi!, VOl. 98 colour and one that is associated with a yellow colour. As would be expected, these compounds give green spots. It is of interest to consider also the effect of the various chemical groupings on the RF values of the parent compound. For both the series based on urea and that based on methylenediurea, the replacement of an amido hydrogen with a methylol group, -CH,.OH, lowers the RF value, while replacement with a methoxymethyl group, -CH,.OCH,, increases the R, value.This relationship is illustrated in Fig. 3 for one solvent system. It has been previously stated that the solvent should be prepared daily. However, during the course of a working day, changes do occur in the solvent system, probably because of the formation of acetamide from the ethyl acetate and ammonia. The only compound that is markedly affected by this solvent change is hexamine (from formaldehyde), which progressively moves to a lower RF value. This shift can be advantageous on occasions, such as when a small amount of urea is to be detected in the presence of a large amount of form- aldehyde. If the chromatogram is run in solvent that is approximately 4 hours old, satis- factory separation can be achieved. Solvent front 0 1 2@ 0 3 40 :::la @5.6 03 0 4 0.4 5 0 010 0.5 110@12 0.3 Fig.2. Positions of the products of the reaction of urea, formaldehyde and methanol on a silica gel plate. Solvent systems: (a), ethyl acetate - methanol - ammonia solution (80 + 16 + 6); and ( b ) , ethyl acetate - methanol - ammonia solution (88 + 6 + 6). The spots are identified following the system used in Fig. 1 : 1 = DMU.DME; 2 = MMU.MME; 3 = DM.MDU.DME; 4 = DMU.MME; 6 = MM.MDU.MME; 6 = urea; 7 = formaldehyde; 8 = DM.MDU.MME; 9 = MMU; 10 = MDU; 11 = DMU; 12 = MM.MDU; 13 = DM.MDU; 14 = DMTU; and a and b are unknown compounds. Colours of spots : open circles, yellow ; closed circles, blue ; and half-closed circles, green During the chromatographic separation of the urea derivatives described in this paper and of other urea condensation mixtures, only two minor spots [(a), yellow and (b), green (see Fig. Z)] have been observed that have not so far been identified.The study of commercial urea - formaldehyde compositions by this method is limited. Because of the multitude of compounds of medium and high relative molecular mass present in these materials, the region of the chromatogram below urea tends to form a streak. This fact, coupled with the coincidence of monomethylolurea and methylenediurea when using both solvent systems, makes the quantitative or semi-quantitative determination of mono- methylolurea and dimethylolurea difficult. The determination of these simple compounds of low relative molecular mass is described in Part 11.February, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART I 115 DMU.DME ! 0-8 1 DM.MDU 4 L Increasing rnethylol Increasing ether substitution substitution Fig. 3. Effect of amido substitu- tion on RB values. Solvent system: ethyl acetate - methanol - ammonia solution (88 + 6 + 6). The compounds are identified following the system used in Fig. 1 I thank Mr. P. Lewis for his interest in the work, his translation of the Japanese papers and for reading the manuscript. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. REFERENCES Hamada, M., J . Chem. SOC. Japan, Ind. Chem. Sect., 1965, 58, 286. Inoue, M., and Kawai, M., “Research Report of the Nagoya Municipal Industrial Research Insti- Ito, Y.. J . Chem. SOC. Jaflan, Ind. Chem. Sect., 1969, 62, 1918. De Jong, J. I., and De Jonge, J., Recl Trav. Chim. Pays-Bas Belg., 1963, 72, 202. Einhorn, A., and Hamburger, A., B e y . dt. chem. Ges., 1908, 41, 24. Walker, J. F., “Formaldehyde,” Third Edition, Reinhold Publishing Corporation, New York, Sally, J. D., and Gray, J. B., J . Amer. Chem. SOC., 1948, 70, 2660. Kadowaki, H., Bull. Chem. SOC. Japan, 1936, 11, 248. U.S. Patent 2,247,419, 1928. tute,” 1957, No. 17, pp. 1-6. -, Ibid., 1961, 64, 382. -, Ibid., 1961, 64, 386. 1964, p. 379. Received June 21st, 1972 Accepted October 6th, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800107

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

116 Analyst, February, 1973, Vol. 98, PP. 116-121 Thin-layer Chromatography of Simple Urea - Formaldehyde - Methanol Reaction Products Part 11.” Quantitative Aspects BY P. R. LUDLAM (The Borden Chemical Company ( U . K . ) Limited, North Baddesley, Southampton, SO6 9ZB) A thin-layer chromatographic method for the determination of urea, monomethylolurea and dimethylolurea in urea - formaldehyde resins is described. The resin is treated with methanolic boron trifluoride, whereby the methylol compounds are quantitatively converted into their respective methyl ethers. Subsequent application of chromatography on silica gel plates that have been previously treated with ammonia vapour in order to prevent reaction of the urea derivatives results in the effective separation of the components of low relative molecular mass, thus allowing their concentrations to be determined.Examples are given illustrating the change in concen- tration of urea derivatives of low relative molecular mass with time in urea - formaldehyde formulations. CURRENTLY many forms of urea - formaldehyde compositions are being produced that contain, to a greater or lesser extent, urea - formaldehyde condensation products of low relative molecular mass. Chromatography of urea - formaldehyde resins for the purpose of separating, identifying and determining these components of low relative molecular mass can throw some light on the nature of a particular material, its age and its method of manufacture. The direct chromatographic determination of urea, monomethylolurea (hydroxymethyl- urea) and dimethylolurea (dihydroxymethylurea) is fraught with many difficulties.Although it is possible both to apply the material to the chromatographic plate so that it is ready for development without significantly altering the composition of the mixture and to develop the chromatogram in such a way that there is a satisfactory separation of some of the compounds of low relative molecular mass, it is found that monomethylolurea and dimethylol- urea can be almost totally obscured by the unresolved fraction of high relative molecular mass, which extends from the origin to the region of monomethylolurea. Further, the fact that monomethylolurea is coincidental with methylenediurea is another major difficulty encountered in the direct chromatography of this type of mixture.Similarly, monomethylol- methylenediurea interferes in the determination of dimethylolurea because of its proximity on the chromatographic p1ate.l Another major drawback to any direct chromatographic method is the inherent instability of monomethylolurea and to a lesser extent dimethylolurea, both in solution and in the solid state. Consequently, the solid reference materials would have to be purified every few days and the standard solutions prepared daily. It is fortunate that most of these difficulties can be overcome by converting the alcohol groups into their methyl ethers. Serious errors can, of course, be introduced into the determination if significant amounts of methyl ethers are present in the mixture before etherification. This problem, however, is not usual but if any doubts exist about the ether concentration, the sample should be checked by running a direct chromatogram prior to carrying out quantitative chromatography.Both monomethylolurea and dimethylolurea ethers have RF values greater than that of urea and are therefore effectively separated from the “tail” of the resin, and, as shown in Part I of this paper,l no compounds have so far been investigated that have RF values of a similar order. If, however, a considerable amount of monomethylolmethylenediurea is present, then interference with urea will result and measurement of the urea concentration will have to be made by direct chromatography, i.e., without ether formation. Only very * For Part I of this series, see p. 107.@ SAC and the author.LUDLAM 117 occasionally is this approach necessary. The stability of the ethers of both mono- and di- methylolurea is much greater than that of the base compounds, which makes it practical to prepare fairly large amounts of the pure compounds, and the standard solutions in methanol can be used for many months without noticeable deterioration occurring. The conversion of the methylol compounds into their methyl ethers must, of course, proceed quantitatively. For all commercial products so far examined the method given below has proved satisfactory. However, should the composition under test be highly alkaline or strongly buffered, it is probable that etherification will not be complete. In this event, trial adjustments of the concentration of boron trifluoride will enable the optimum methylating conditions to be determined and allow quantitative conversion to be achieved.EXPERIMENTAL CONVERSION OF METHYLOL COMPOUNDS INTO THEIR METHYL ETHERS- Initial experiments showed that with 1 per cent. of boron trifluoride or hydrogen chloride in methanol, monomethylolurea and dimethylolurea could be quantitatively converted into their ethers within 1 minute. However, after 3 minutes small amounts of mono- and di- methylolurea had been regenerated in the solution. This effect was more noticeable after 5 minutes, by which time compounds of high relative molecular mass were being precipitated out of solution. It was obvious that the concentration of the catalyst would have to be controlled very carefully, and at this stage it was decided to concentrate on boron trifluoride as the catalyst as it was considered that buffers, which occur in commercial compositions, may have less effect on the catalytic activity of boron trifluoride than that of hydrogen chloride.Further experiments with methanolic boron trifluoride solutions showed that a 0.16 per cent. solution would quantitatively convert mono- and dimethylolurea into their ethers after 15 minutes and that the solution was stable for a further 20 minutes, thus giving adequate time for sample preparation and manipulation. EFFECT OF BUFFERS ON THE ETHERIFICATION PROCESS- Sodium formate, disodium hydrogen orthophosphate and triethanolamine are three buffers that can either be formed in, or added to, commercial urea - formaldehyde resins.The effect of such compounds on the etherification of a mixture of mono- and dimethylolurea is shown in Table I. The efficiency of a particular set of methylating conditions is indicated by the amount of monomethylolurea that remains. TABLE I EFFECT OF BUFFERS ON ETHERIFICATION Ratio of Buffer in sample, per cent. Monomethylolurea, per cent., A BF, in methyl- c \ remaining after- anol, reagent to ethanol- 2 6 10 16 20 meth- ating Tri- f A \ per cent. sample HCOONa Na,HPO,. 12H,O amine minutes minutes minutes minutes minutes - - - 0.16 6: 1 1.8 0 0 100 - 100 0-26 3: 1 0-25 0 0 - 100 - - 10 10 10 - 10 0 1 0 - (10 <lo <10 0 0 0.6 10 <lo - - 10 0 0 0.66 10 - 0-60 3: 1 0.26 0 0 <10 (10 <lo - - 0.66 0 0 - 60 0 0 1.8 100 0.60 0 0 20 10 0.66 0 0 80 - - - - 60 - - - - < 10 - < 10 - As can be seen in Table I, ether formation appears to be mostly affected by sodium formate.However, the concentration in urea - formaldehyde resins is not likely to exceed 0.6 per cent. and etherification with a 0-5 per cent. solution of boron trifluoride in methanol for 15 minutes is likely to prove effective in most instances. Should the buffer content be unusually high, then the presence of monomethylolurea will be observed on the developed chromatogram, and further experiments will be necessary so as to ascertain the most suitable methylating conditions for that particular composition.118 LUDLAM : THIN-LAYER CHROMATOGRAPHY OF SIMPLE [Analyst, VOl. 98 EFFECT OF WATER ON THE ETHERIFICATION PROCESS- Experiments on the methylation of mono- and dimethylolurea, in which the methanol to water ratio varied from 2: 1 to 6: 1, showed that in the presence of a large percentage of water the conversion of a methylol compound into its ether was very poor, much of the original material remaining unchanged. At ratios of 5: 1 or above, the reaction became quantitative.To allow for possible variations in the water content of the sample, a methanol to sample ratio of 4: 1 was adopted for the method. Thus, with 35 per cent. of water in the sample, the over-all methanol to water ratio will be of the order of 12: 1. METHOD APPARATUS- over silica gel. Thin-layer chromatographic plates-Merck Kieselgel F,,, (fast running) on glass. Store Microfiif&ks, 1 , 2 and 5 $-Constriction pipettes or Drummond “Microcaps.” Chromatographic tank.MATERIALS- Urea-Analytical-reagent grade. Prepare standard solutions in methanol, 0.4 to 2.0 per cent. m/V in intervals of 0.2 per cent. Dimethylolurea dimethyl ether-Prepare according to the method given in Part 1 .l Prepare standard solutions in methanol equivalent to 0.8 to 3.0 per cent. m/V of dimethylolurea, in intervals of 0.2 per cent. Monomethylolurea monomethyl ether-Prepare according to the method given in Part 1 .I Prepare standard solutions in methanol equivalent to 0.8 to 3.0 per cent. m/V of mono- methylolurea, in intervals of 0.2 per cent. These solutions are stable for at least 6 months. Eluting solvent-Mix 44 ml of ethyl acetate with 3 ml of methanol and 3 ml of ammonia solution of sp. gr. 0.88.Allow the mixture to stand for 1 hour before use. Prepare freshly each day. Chlorine-As supplied in a cylinder (BDH Chemicals Ltd.) . Spray reagent-Dissolve 5 g of o-toluidine in 95 ml of acetic acid. Boron tri$uoride, 0.5 per cent. solution in methanol-Dilute the 14 per cent. solution of boron trifluoride in methanol (BDH Chemicals Ltd.) with methanol. PROCEDURE- To 1 g (or less) of sample, add dropwise with vigorous stirring, 0.5 per cent. of boron trifluoride in methanol so as to obtain a final volume of 5 ml. It is recommended that a pre-calibrated test-tube or a small measuring cylinder is used for the preparation of the sample. A calibrated flask is not suitable owing to the method of sample treatment. Allow the solution to stand for 15 minutes. Place the chromatographic plate in the vapour of the eluting solvent for a few seconds, remove the plate and spot on to it 1 pl of each of the standard solutions.Spot on to the plate 1, 2 and 5 pl of the sample solution. Allow the spots to dry and place the plate in the solvent in the chromatographic tank. It is not necessary to saturate the atmosphere of the tank with solvent vapour. When the solvent has risen almost to the top of the plate, remove the plate from the tank and allow it to dry for 15 minutes at room temperature. Do not dry it at elevated temperatures. Expose the dry plate to chlorine gas either in a separate vessel or by directing chlorine gas from the cylinder directly on to the plate in an efficient fume hood. Allow the excess of chlorine to disperse from the plate for a t least 5 minutes and spray with the 6 per cent.o-toluidine solution. Do not expose the plate unnecessarily to bright light. Evaluate the plate after half an hour. Foreknowledge of the approximate concentrations of urea and mono- and dimethylolurea in a sample can permit a smaller range of standards and sample to be used. The procedure allows urea to be determined at concentrations from 0.5 to 10 per cent. and mono- and dimethylolurea at concentrations from 0.8 to 15 per cent.February, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART 11 119 RESULTS AND DISCUSSION Mixtures of urea and mono- and dimethylolurea, in which the balance was methylene- diurea, were analysed by the method given above (on a 0.25-g sample). The results are given in Table 11.TABLE I1 ANALYSIS OF MIXTURES OF UREA, MONOMETHYLOLUREA AND DIMETHYLOLUREA Monomethylolurea, Dimethylolurea, Urea, per cent. per cent. per cent. - r - Sample* Theoretical Experimental Theoretical Experimental Theoretical Experimental A 16 (i) 16 f 3 26 (4 17 * 3t 37 (i) 36 f 3 (ii) 36 f 3 B 20 20 f 2 30 33 f 3 46 46 f 3 (ii) 15 f 3 (ii) 26 f 3 * In each sample the balance of the content was methylenediurea. t This very low result is possibly due to pre-reaction of the monomethylolurea during the sample There is little doubt that if this type of mixture is ground and left for several hours, preparation stage. reaction will occur even if the sample is dry. A detailed examination of the plate showed that , except for A (i) , no significant amounts of the original methylol compounds remained, nor were any spots present other than those of urea, methylenediurea and the methyl ethers of mono- and dimethylolurea, thus indicating that side reactions had not occurred.NH,.CO.NH, + CH20 + NH,.CO.NH.CH,.OH by measuring the residual formaldehyde in the reaction mixture. The following experiment was designed to determine the rate constant, k,, by measuring the residual urea and the monomethylolurea formed in the reaction. Urea (log) was added to 30g of 36 per cent. formaldehyde solution (molar ratio of urea to formaldehyde, 1:2*16) at pH 7-0. The temperature was maintained at 25 "C in a water-bath and the pH at 7.0 by the addition of 0.1 N sodium hydroxide solution. After 20 minutes, a sample was analysed by the chromatographic method and the following results were obtained: urea 18, monomethylolurea 10 and dimethylolurea 1 per cent.The rate constant, k,, calculated from the residual urea content is 0.79 x 10-4, which is in good agreement with De Jong and De Jonge's value of 0.6 x The experimental value of the monomethylolurea concentration (10 per cent.) is in good agreement with the value of 10.5 per cent. calculated from the change in urea concentration (26 to 18 per cent.). Two liquid urea - formaldehyde resins, stored at 21 "C, were monitored for a 3-month period in order to determine the variation of free urea and mono- and dimethylolurea with time. It is common practice with compositions of this type to add urea towards the end De Jong and De Jonge2 have determined rate constants for the reaction w a +.' s 8- m ? 5 - 0 > - .- E n 6 1 I I I I I I I t 40 60 80 1 2 4 6 8 1 0 20 Tirne/days (logarithmic scale) 00 Fig.1. Variation of dimethylolurea content with time (resin A)’ O 1 ki a Time/days (logarithmic scale) Fig. 2. Variation of urea (A), monomethyl- olurea (B) and dimethylolurea (C) contents with time (resin B) Solvent front Origin 0 0 0 0 0 0 Q Fig. 3. Thin-layer chromatogram of a methylated urea resin and standards. Spots 1, 2 and 3, 1 p1 of 0.5, 0.75 and 1.0 per cent. urea solutions, respectively; spots 4, 8 and 12, 1 p1 of resin solution (10 per cent.); spots 5, 6 and 7, 1 pl of 0.8, 1.0 and 1.2 per cent. monomethylolurea monomethyl ether solutions, respectively; and spots 9, 10 and 11, 1 pl of 1.0, 1.2 and 1.5 per cent.dimethylolurea dimethyl ether solutions, respectively. Spots a t A are dimethylolurea dimethyl ether; a t B, monomethylolurea monomethyl ether; a t C, dimethylol- methylenediurea dimethyl ether; a t D, urea; and a t E, methylene- diurea. Colours of spots: open spots, yellow; closed spots, blue; and half-closed spots, greenFebruary, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART 11 121 of manufacture to reduce the level of free formaldehyde. One of the resins (A) did not contain “end” urea; the other (B) contained 11.6 per cent. The urea and monomethylolurea contents of resin A were as follows- 1st day 6th day 10th day 20th day 40th day 60th day Urea, per cent. . . .. . . <0.6 <Om6 <Ow6 <Om6 <0.6 <0*6 Monomethylolurea, per cent. . . 1.6 1.0 1.0 0.6 0.6 < 0.5 The dimethylolurea content is shown in Fig. 1. The urea and mono- and dimethylolurea contents of resin B are shown in Fig. 2. A typical chromatogram is illustrated in Fig. 3. Examination of the many chromatograms obtained in the course of this study shows that only two other compounds of low relative molecular mass are present to any significant extent in normal urea - formaldehyde resins. These compounds are methylenediurea, up to approximately 1 per cent., and dimethylolmethylenediurea, perhaps up to 6 per cent. Two minor spots, both of which probably amounted to less than 1 per cent., occur above dimethylolurea dimethyl ether on the chromatogram and it is probable that these are due to compounds formed in the etherification reaction, which so far have not been identified. REFERENCES I thank Mr. J. G. King for his skilful technical assistance. 1. 2. Ludlam, P. R., Analyst, 1973, 98, 107. De Jong, J . I., and De Jonge, J., Reel Trav. Chim. Pays-Bas Belg., 1962, 71, 643. NOTE-Reference 1 is to Part 1 of this series. Received June 21st, 1972 Accepted October 6th, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800116

出版商:RSC    

年代:1973

数据来源: RSC