82 Analyst, February, 1974, Vol. 99, pp. 82-92 Ionic Polymerisation as a Means of End-point Indication in Non-aqueous Thermometric Titrimetry Part V.* The Iodimetric Determination of Organic Bases, Hydrazine Derivatives and Water BY E. J. GREENHOW AND L. E. SPENCER (Department of Chemistry, Chelsea College, University of London, Manresa Road, London, S . W.3) A thermometric titration method has been evaluated in which organic bases, hydrazines, phosphines and quaternary ammonium halides, and also water, have been titrated with iodine in non-aqueous solutions containing alkyl vinyl ethers. The latter polymerise with the excess of iodine evolving heat, which marks the end-point. The ratio of the reactants in titrations of most of the amines examined, namely 3.6 to 4.6 atoms or 1.8 to 2.3 molecules of iodine to 1 molecule of amine, depending on the amine, is favourable to the titration.With hydrazine derivatives, the ratio ranges from 4-2 to less than 1 atom of iodine to 1 molecule of the hydrazine, depending on the hydrazine derivative. Water can be titrated with iodine in the presence of alkyl vinyl ethers, about thirteen molecules of water consuming one atom of iodine. The end-point in titrations of most of the compounds examined is marked by a sharp inflection in the titration graph when an automatic procedure is used. Precisions are usually better than 1 per cent. with 0-05 M and 2 per cent. with 0-01 M titrant solutions. Sample sizes down to about 0-0005 mmol, depending on the iodine consumed in the reaction, can be determined with 0.01 M titrant solution.Calibration graphs show that, except in the titration of water, the volume of titrant and amount of sample are linearly related in the range 0 to 1 ml of titrant. The curvatures of calibration graphs for water depend on the rates of addition of iodine to the sample; linearity can almost be achieved a t an appropriate titration rate. It is suggested that the stoicheiometry, i.e., the iodine consumed per molecule of sample, is a quantitative measurement of the basic properties of the compounds investigated. The different stoicheiometries for different compounds make the iodimetric method useful for the selective determination of the constituents of binary mixtures of bases and hydrazine derivatives, but unsuitable for the determination of the total basic or hydrazine function in more complex mixtures.THE determination of organic bases by iodimetric titration has not previously been considered, although reactions between pyridine and iodine at ambient temperature were reported as early as 1895.l Pyridinium bromide perbromide (C,H,N.HBr.Br,) and trimethylphenyl- ammonium tribromide are available as laboratory reagents but the simple amine - halogen addition compounds appear to have received little attention. Indeed, in a recent edition of one of the standard works on organic chemistry,2 it is noted that the reaction between halogens and primary and secondary amines “does not give useful products.” The titration of organic hydrazine derivatives with iodine, bromine or binary inter- halogen compounds of iodine, bromine and chlorine, is an established assay pr~cedure.~ The oxidation reaction is usually, but not always, accompanied by the evolution of nitrogen.With hydrazides, four atoms, i e . , two molecules, of iodine are normally consumed by one molecule of hydrazide, but it has been pointed out3 that reactions of halogens with hydrazine derivatives in general may be complicated by there being more than one possible route and, consequently, variations in the stoicheiometry. It has been stressed that strict adherence to experimental conditions is necessary in order to obtain reproducible results. * For Part IV of this series, see Analyst, 1973, 98, 485. @ SAC and the authors.GREENHOW AND SPENCER 83 Iodimetry, in the form of the Karl Fischer reaction, is the most important chemical method for the determination of water in organic solvents.In this reaction, two atoms of iodine are, in theory, consumed by one molecule of water. Siggia4 has shown that iodine reacts with vinyl ethers in the presence of an alcohol according to the following equation : ROCH=CH, + I, + R’OH -+ ROCH(OR’)CH,I + HI It would seem likely, therefore, that water should undergo a similar reaction in which two atoms of iodine would correspond to one molecule of water. The reaction product in this instance, ROCH(OH)CH,I, could conceivably react with further iodine and vinyl ether, raising the reaction ratio to four atoms of iodine to one molecule of water. The use of catalytic thermometric titration for the determination of organic bases is described in Part I.5 More recently, a catalytic thermometric procedure has been reported6 for the determination of hydrazine derivatives and xanthates and, less effectively, for thiols. In this procedure iodine was used as the titrant and as a catalyst for the cationic polymerisa- tion process that indicates the end-point, and ethyl vinyl ether was used as the monomer.A detailed investigation of this procedure, which forms the basis of the present paper, has shown that in non-aqueous solution iodine can be used as a titrant not only for certain oxidisable compounds, such as hydrazine derivatives, but also for organic bases and water. A number of organic solvents for the titrant (iodine) and titrands have been assessed in an effort to achieve the optimum determination conditions.In addition, iodine bromide and iodine chloride have been examined as alternative titrants and some alkyl vinyl ethers other than ethyl vinyl ether have been examined as alternative monomers. EXPERIMENTAL REAGENTS- Laboratory-reagent grade dimethylformamide, toluene, pyridine, NN-dimethylacetamide, 1,2-dichloroethane, tetrahydrothiophene 1,l-dioxide (sulpholane) and dimethyl sulphoxide were dried over molecular sieve 4A before use. Iodine and acetic acid (both AnalaR grade) were used as received. Ethyl vinyl ether, n-butyl vinyl ether, 2-chloroethyl vinyl ether, isobutyl vinyl ether, other organic bases, benzoic acid, iodine bromide, iodine chloride and iodine trichloride were laboratory-reagent grade materials and were used without further purification.Divinyl ether was extracted with distilled water and dried over alumina before use. Benzenesulphonohydrazide, 4,4’-oxybis (benzenesulphonohydrazide) and 2-h ydroxyethyl- hydrazine were gifts from Fisons Limited, Agrochemicals Division. Other hydrazine deriva- tives were laboratory-reagent grade materials. Solutions of iodine, 0.05 and 0.01 M in organic solvents, were standardised by adding to 20 ml of the solutions 50 ml of water, 1 g of potassium iodide and 3 ml of 1 M sulphuric acid, and titrating with 0.1 and 0.01 M sodium thiosulphate solutions, respectively, with starch as indicator. Solutions of iodine chloride, iodine trichloride and iodine bromide in dimethylformamide, all 0.05 M, were standardised by the method used for 0.05 M iodine solution.APPARATUS- For thermometric titration-Use the automatic apparatus described in Part III7 with an 8-ml tit r at ion flask. For gasometric determinations-Use a 50-ml gas burette, connected to a 50-ml, mag- netically stirred reaction vessel with a side-arm that is fitted with a serum cap. Details of the apparatus were given by Dixon8 PROCEDURE- Thermometric titration-Prepare a solution of the sample in dimethylformamide or in another appropriate solvent. The concentration will depend on the stoicheiometry of the reaction with iodine and on the titrant concentration; thus 1 ml of the solution should contain about 0.1 mequiv of the sample compound when the 0.05 M titrant is used and about 0.02 mequiv with 0.01 M titrant.84 GREENHOW AND SPENCER: IONIC POLYMERISATION FOR END-POINT [Analyst, Vol.99 Transfer by pipette 1 ml of the sample solution into the reaction flask, add 2 ml of ethyl vinyl ether, stir the solution, then add titrant at the rate of about 0.1 ml min-1 from the motor-driven syringe. The titrant volume at the end-point is taken to be the volume corresponding to the point of inflection in the titration graph. When this inflection is in- distinct, the end-point is taken to be the point where the tangent to the main heat rise leaves the graph at its lower temperature end. Carry out a blank titration by using an equal volume of the same batch of solvent, with the same water content, as that used for the sample titration. The chart recorder of the automatic titration apparatus is conveniently operated at a chart speed of 600 mm h-l and in the range 0 to 100 mV with 0.05 M titrant and 0 to 50 mV with 0.01 M titrant.Gasometric determinations-Transfer by pipette 5 ml of a 0.8 M solution of iodine in dimethylformamide into the reaction vessel, sweep out the air in the vessel with dry nitrogen and connect the vessel to the gas burette. Stir the iodine solution and add, by injection from a syringe through the serum cap, 1-ml aliquots of a 0.18 M solution of the hydrazine derivative in dimethylformamide at 5-minute intervals, reading the gas burette immediately before each injection. Correct the observed increases in volume to volumes at S.T.P. and subtract from these values the volume (1 ml) of the sample solution injected. For the reverse of the above procedure, i e ., addition of aliquots of iodine to an excess of the hydrazide, carry out the above operations, but with 4 mmol of hydrazide dissolved in 10 ml of dimethylformamide in the reaction flask and with 1-ml aliquots of 0.5 M iodine. RESULTS AND DISCUSSION A further investigation of the catalytic thermometric titration of isonicotinoylhydrazine with iodine in dimethylformamide solution, reported briefly in an earlier paper,6 has revealed that: (a), addition of an equimolar amount of acetic or benzoic acid to the hydrazide prior to titration has a negligible effect on the titration value; (b), addition of small amounts, e.g., 1 per cent., of pyridine or water to the hydrazide prior to titration significantly increases the titration value but does not reduce the sharpness of the end-point; and (c), benzoyl- hydrazine requires much less titrant (1.4 atoms of iodine per molecule) than does isonicotinoyl- hydrazine (4.2 atoms of iodine per molecule).Observation ( b ) above indicates that both pyridine and water are titrated iodimetrically by the catalytic thermometric procedure. By using the procedure, a number of pyridine derivatives, primary, secondary and tertiary aliphatic and alicyclic amines, quaternary ammonium halides, organophosphorus derivatives and heterocyclic compounds containing two nitrogen atoms, have been deter- mined. In Table I the compounds are listed and the reactivities in terms of the number of atoms of iodine combining with one molecule of the compound are given. Typical titration graphs are shown in Figs.1 and 6. It can be seen that, if the inflection point of the iodimetric titration is taken as the basis for the calculation, pyridine combines with 4.1 atoms of iodine in dimethylformamide solution. This result agrees well with the formula C,H5N.2I, obtained by Prescott and Trowbridge1 for the crystalline adduct of iodine with pyridine. Most of the aliphatic amines and pyridine derivatives required from 3.6 to 4.6 atoms of iodine for each molecule in the titration. It is interesting to note that the secondary amines are less reactive towards iodine than are the tertiary amines, including the pyridine deriva- tives, although the dissociation constants of aliphatic bases show the secondary amines to be stronger bases than the tertiary amines in aqueous solution.Aniline and the alkylanilines, as might be expected from their weakly basic character, show much lower reactivity towards iodine. Substitution of electron-withdrawing groups on the aniline and pyridine rings causes a reduction in the reactivity towards iodine. Thus, +-nitroaniline does not combine with iodine and 2,6-pyridinedicarboxylic acid shows very low reactivity. Diphenylamine and triphenylamine are unreactive for the same reason. In contrast with triphenylamine, triphenylphosphine combines with iodine in the ratio of about 1 atom of iodine to 1 molecule of triphenylphosphine but the inflection at the end- point is not sharp (Fig. 1). The N-oxides of pyridine and 3-picoline were found to react with iodine in an approxi- mate ratio of 2 atoms of iodine to 1 molecule of the N-oxide but, again, there was no distinctFebruary, 19741 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY.PART v 85 TABLE I ORGANIC BASES AND QUATERNARY AMMONIUM HALIDES TITRATED WITH 0-05 M IODINE IN DIMETHYLFORMAMIDE Conditions: 0.025 mmol of base or halide in 1 rnl of dirnethylformamide added to 2 ml of ethyl vinyl ether and titrated by the thermometric procedure Aliphatic and alicyclic amines- n-Butylamine (3.6) ; benzylamine (3.7) ; 1,2-dianiinoethane (6.75) ; morpholine (3.6) ; piperidine (3.6) ; triethylamine (4.2) ; tris(hydroxymethy1)methylamine (4.3) ; 2-NN-diethylaminopropio- nitrile (4.4) ; N-methylmorpholine (4.6) ; and N-ethylpiperidine (4-4) Pyridine (4.1) ; a-picoline (3.8) ; 2,6-lutidine (4.0) ; 2,6-pyridinedicarboxylic acid (0.09) ; pyridine N-oxide (2.2) ; 3-picoline N-oxide (2.2) ; quinoline (4.1) ; 4-methylquinoline (4.3) ; 8-hydroxy- quinoline (2.1) ; and 2-hydroxyquinoline (0) Aniline (1.3) ; o-toluidine (1.5) ; p-toluidine (1.8) ; p-nitroaniline (0) ; diphenylamine (0) ; and triphenylamine (0) Hexamethylenetetramine (5.0) ; phthalazine (3.5) ; quinoxaline (0) ; and benzimidazole (4.0).Tetra-n-butylammonium bromide (1 -8) : tetra-n-butylammonium iodide (1-5) ; cetyltrimethyl- ammonium bromide (1.4) ; cetylpyridinium bromide (1.8) ; and benzyldimethylmyristyl- ammonium chloride (2.4) Triphenylphosphine (1.1) ; and triphenylphosphine oxide (0) Figures in parentheses following the name of the compound denote the number of iodine atoms combining with one molecule of the compound on the basis of the iodimetric titration. Pyridine derivatives- Aniline derivatives- Heterocyclic nitrogen compounds- Quniernary ammonium halides- Phosphorus compounds- inflection point in the titration graph and the end-points were difficult to establish (Fig.1). Triphenylphosphine oxide did not react with iodine. Quinoline and 4-methylquinoline are similar to pyridine and the methylpyridines in their reactivities towards iodine, but 8-hydroxyquinoline is far less reactive and 2-hydroxy- quinoline shows no reaction. Presumably hydrogen bonding in the last two compounds inhibits or prevents formation of adducts with iodine. a h 1 I 1 I 0.05~ iodine reagent/ml (1 division = 0.5 ml) Fig. 1. Catalytic thermometric titration of organic bases, water and quaternary ammonium halides with 0.05 M iodine reagent. Compounds/mg : a, n-butylamine, 0.84; b, tris(hydroxymethyl)methylamine, 1-2 ; c, pyridine, 1.3 ; d, hexamethylenetetramine, 1.6; e, morpholine, 1-89: f, 8-hydroxyquinoline, 2.9; g, pyridine N-oxide, 2.3; h, tri- phenylphosphine, 7.4 ; j, cetyltrimethylammonium bromide, 4.0 ; k, tetra-n-butylammon- ium iodide, 9.3 ; m, benzyldimethylmyristylammonium chloride, 5.0 ; and w, water, 10.086 GREENHOW AND SPENCER: IONIC POLYMERISATION FOR END-POINT [Analyst, Vol.99 A number of heterocyclic compounds containing more than one ring nitrogen atom have been titrated. Hexamethylenetetramine combines with only five atoms of iodine instead of the possible sixteen, calculated on the basis of four atoms of iodine for each nitrogen atom.Quinoxaline proved to be unreactive but phthalazine, an isomer of quinoxaline, com- bined with 3-5 atoms of iodine per molecule. Presumably the more remote nitrogen atoms in phthalazine are less affected by the benzene ring. Benzimidazole, with one of its two nitrogen atoms unconjugated to the benzene ring, is even more reactive than phthalazine. Quaternary ammonium halides, including alkylpyridinium halides, can be titrated by means of this iodimetric method. With the compounds examined it was found that from 1.4 to 2.4 atoms of iodine combined with one molecule of the halide. There appears to be a tendency to form trihalides, which are known to be stable systems, and for the halide ion to influence the reactivity. The possibility of water reacting with iodine in the presence of vinyl ethers was discussed in the introduction.It has been confirmed that water can be titrated in solution in dimethyl- formamide and that a sharp end-point is obtained (Figs. 1 and 6). There is some indication that the presence of water increases the sharpness of the end-point in the titration of other compounds. In the titration of water, the consumption of the iodine titrant at the indicated end-point is dependent on the rate of addition of the titrant, as shown in Fig. 2. It can be seen that there is an almost linear relationship between the water content of the sample and the titrant required when titrant is added a t a rate of 0.06ml min-l. This rate would, therefore, be the recommended rate of addition of titrant in the determination of water and, at this rate of addition, about one atom of iodine is consumed by thirteen molecules of water.Clearly, the method is not highly sensitive for the determination of water because 23.4 mg of water would require only 1 ml of 0.05 M iodine solution on the basis of the above reaction ratio. 0.05~ iodine reagent/ml Fig. 2. Effect of the rate of addition of titrant on calibration graphs in the thermometric titration of water with 0.05 M iodine reagent. Rate of addition of titrantlml mi@: a, 0.02; b, 0.032; c, 0.06; d, 0.12; e, 0.20; and f, 0.60 The reaction of water, iodine and ethylvinylether in dimethylformamide does not appear to be simple and, if it is similar to the reaction described by Siggia4 for alcohols, obviously does not proceed to completion during the course of the titration.It is possible, however, that water is being titrated merely as a weak base. As water is titrated, an allowance must be made when organic solvents containing trace amounts of water are used in the titration of bases, hydrazine derivatives, etc. A convenient procedure is to carry out a blank titration on an equal volume of the same solvent, takenFebruary, 19741 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART v 87 from the same batch as that used for dissolving the sample. With dimethylformamide dried over molecular sieve 4A, the blank titration with 0-05 M iodine is about 0.15 ml. It is important, of course, that the sample itself should be dry. In addition to isonicotinoylhydrazine, a number of other hydrazine derivatives have been determined, including hydroxyalkyl-, dialkyl-, aryl- and diarylhydrazines, arylhydra- zides, arylsulphonohydrazides and semicarbazides. In Table 11, the reactivities of these compounds towards iodine are given in terms of iodine atoms per molecule.TABLE I1 HYDRAZINE DERIVATIVES TITRATED WITH 0.05 M IODINE I N DIMETHYLFORMAMIDE Conditions: Sufficient compound to give a titration value of about 0.5 ml is dissolved in 1 ml of dimethylformamide, added to 2 ml of ethyl vinyl ether and titrated by the thermometric procedure NiV-Dimethylhydrazine (3.4) ; 2-hydroxyethylhydrazine (2.2) ; phenylhydrazine (1 -0) ; 4-nitro- phenylhydrazine (1.1) ; 2,4-dinitrophenylhydrazine (0.18) ; NN-diphenylhydrazine (0.86) ; benzoyl- hydrazine (1.4) ; isonicotinoylhydrazine (4.2) ; benzenesulphonohydrazide (0.33) ; 4,4’-oxybis(ben- zenesulphonohydrazide) (0.63) ; semicarbazide hydrochloride ( 1.9) ; and thiosemicarbazide (3.1) Figures in parentheses following the name of the compound denote the number of iodine atoms combining with one molecule of the compound on the basis of the iodimetric titration.The alkylhydrazines, i.e., NN-dimethylhydrazine and 2-hydroxyethylhydrazine, were the most reactive of the hydrazine derivatives examined, if one excepts thiosemicarbazide and isonicotinoylhydrazine, which possess reactive groups other than the hydrazine group. Titration graphs for some of the hydrazine derivatives are shown in Fig. 3. It can be seen that in the titration of benzenesulphonohydrazide, 4,4‘-oxybis(benzenesu1phonohydrazide) a h” 0.05~ iodine reagent/ml (1 division = 0.5 ml) Fig.3. Catalytic thermometric titration of hydrazine derivatives with 0.05 M iodine reagent. Compounds/mg : a, 2-hydroxyethylhydrazine, 1.1 ; b, NN-dimethyl- hydrazine, 0.65; c, NN-diphenylhydrazine, 9-2 ; d, 4-nitrophenylhydrazine, 5.1 ; e, 2,4- dinitrophenylhydrazine, 20.2 ; f, benzoylhydrazine, 3.4; g, isonicotinoylhydrazine, 0.85 ; h, * phenylhydrazine, 11.0; j, 4,4’-oxybis(benzenesulphonohydrazide), 26.6 ; and k, * benzenesulphonohydrazide, 28.9. * Titrant, 1 division = 0.83 ml; temperature, 1 division = 2.0 “C88 GREENHOW AND SPENCER: IONIC POLYMERISATION FOR END-POINT [Analyst, Vol. 99 and phenylhydrazine, iodine is consumed after the first sharp inflection in the titration graph, which has been taken as marking the end-point of the titration.It is probable that a slow evolution of nitrogen occurs after the initial reaction with iodine and, ultimately, four atoms iodine would be required for each hydrazine group. Any further reaction with nitrogen evolution would, of course, be accelerated by the rising temperature caused by the ionic polymerisat ion. Observations (b) and (c) above suggest that, in dirnethylformamide, iodine reacts with the heterocyclic nitrogen as well as with the hydrazine group of the isonicotinoylhydrazine. If the reaction of the 4.2 atoms of iodine with each molecule of isonicotinoylhydrazine occurred only at the hydrazine group, the reaction could be explained essentially by an equation similar to that which applies to the reaction in aqueous solution: In this instance a molecule of nitrogen would be liberated from each molecule of hydrazide.Gasometric experiments with hydrazides have been carried out to determine whether the iodine reactant is consumed in reactions involving the evolution of a gas. Aliquots (1 ml) of a solution of isonicotinoylhydrazine in dimethylformamide were added to an excess of iodine in 5 ml of dimethylformamide at ambient temperature (25 “C in this experiment) and the volume of nitrogen evolved after the addition of each aliquot was measured. The experiment was then repeated with benzoylhydrazine. The results of the experiment are summarised in Fig. 4. With both hydrazides, the rate of evolution of nitrogen after addition of the second aliquot was almost constant until five aliquots had been added, when it began to decrease.During the “steady state,” the rate of nitrogen evolution was about the same for both hydrazides, 0.6 mmol of nitrogen being released from each millimole of hydrazide, which is equivalent to a reaction ratio of 2.4 atoms of iodine to 1 molecule of hydrazide if two molecules of iodine are required for the release of one molecule of nitrogen. 0.1 8 M hydrazide in .dimethyl f ormamide/mmol 5 0 1 2 3 4 5 0.5 M iodine in dirnethylforrnarnidefmrnol Fig. 4. Gasometric measurements in the reaction of isonicotinoylhydrazine and benzoylhydrazine with iodine in dimethylformamide solution : a, addition of 0.18- mmol aliquots of isonicotinoylhydrazine to 4 mmol of iodine; b, addition of 0-18-mmol aliquots of benzoylhydrazine to 4 mmol of iodine; c, addition of 0.5-mmol aliquots of iodine to 4 mmol of benzoylhydrazine; and d.addition of 0.5-mmol aliquots of iodine to 4 mmol of isonicotinoylhydrazine The experimental conditions are not the same as those obtaining in the iodimetric titration because the ethyl vinyl ether is omitted for obvious reasons. However, it is reasonable to assume that the reactivities of the two hydrazides are similar when measured by the amount of nitrogen evolved and that the much greater consumption of iodine by isonicotinoylhydrazine,February, 19741 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART v 89 4.2 atoms compared with 1.4 atoms per molecule, is caused by a reaction involving the heterocyclic nitrogen of the latter compound.When the reverse procedure is carried out, i.e., when l-ml aliquots of iodine are added to an excess of the hydrazide in dimethylf onnarnide, nitrogen is evolved immediately following addition of the first aliquot in both instances (Fig. 4). Thus, there is no evidence from this experiment that with isonicotinoylhydrazine a reaction with the heterocyclic nitrogen takes precedence over a reaction with the hydrazide group. With all of the samples examined, except water, calibration graphs proved to be linear in the range 0 to 1 ml of titrant when titrant was added at rates of 0.05 to 0.2 ml min-l. The effect of the rate of titrant addition on the calibration graph for isonicotinoylhydrazine is shown in Fig. 5. Increasing the rate of addition of the titrant can be seen to displace the linear calibration, but, because the lines are parallel, the calibration factor remains constant 0-75 0.05~ iodine reagedm1 Fig.5. Effect of the rate of addition of titrant on calibration graphs in the thermometric titration of isonicotinoyl- hydrazine with 0-05 M iodine reagent. Rate of addition of titrantlml min-1: a, 0.02; b, 0.032; c, 0.06; d, 0.12; and e, 0-20 The sharp inflection at the end-point with most of the titrations gives this catalytic thermometric method a slightly higher precision than the corresponding acid - base titrations described in Parts I5 and 11,9 in which the 0.05 M titrant was used. With this titrant, coefficients of variation of less than 1 per cent. have been obtained in most of the titrations. With 0.01 M titrant, sharp end-point inflections were still obtained but the precision was of the order of 2 per cent.Some precision values are given in Table 111. Titration graphs obtained with 0.01 and 0.005 M titrants are shown in Fig. 6. A number of solvents have been examined as possible alternatives to dimethylformamide. Toluene, NN-dimethylacetamide, 1,2-dichloroethaneJ tetrahydrothiophene 1, l-dioxide (sul- pholane), propylene carbonate and 2-methoxypropionitrile can be used as solvents for the iodine titrant or for the sample. Toluene gives less sharp end-points than does dimethyl- formamide with some compounds and the latter solvent has been preferred in the present study. Several alkyl vinyl ethers were assessed before ethyl vinyl ether was chosen as the monomer for this detailed investigation.The alternatives, n-butyl vinyl ether, isobutyl vinyl ether, 2-chloroethyl vinyl ether and divinyl ether, all proved to be inferior to the chosen monomer. No discernible end-points were obtained with the last two ethers but n-butyl and isobutyl vinyl ethers gave acceptable end-points in the titration of amines (Fig. 7). As interhalogen compounds, such as iodine bromide and iodine chloride, have been used as titrants in oxidation - reduction reactions, some of these compounds, namely iodine bromide, iodine chloride and iodine trichloride, have been tried as alternatives to iodine90 GREENHOW AND SPENCER : IONIC POLYMERISATION FOR END-POINT {ArtdySt, VOl. 99 TABLE I11 RESULTS FOR PRECISION FROM THE THERMOMETRIC TITRATIOX OF ORGANIC BASES, HYDRAZINE DERIVATIVES AND WATER WITH 0.05 AND 0.01 M IODINE SOLUTION IN DIMETHYLFORMAMIDE" Compound Pyridine * ... .. Benzoylhydrazine . . . . Tris(hydroxymethy1) methylamine NN-Dimethylhydrazine . . Isonicotinoylhydrazine . . Benzenesulphonohydrazide . . Thiosemicarbazide . . .. Water . . .. . . .. Tris (hydroxymethyl) methylamine Isonicotinoylhydrazine . . a-Picoline . . .. .. Amount takenlmg . . 1-03 . . 1.20 . . 0.86 . . 6.64 . . 1-70 . . 28.9 . . 2.34 . . 17.0 . . 0.24 . . 0.34 . . 0.28 Ti tran t Mean molarityt n$ titre/ml 0.05 0.05 0.05 0.05 0-05 0.05 0.05 0.05 0.0 1 0.01 0.01 4 3 4 3 4 3 3 4 3 3 3 0.49 0.62 0.44 0.66 0.38 0-55 0.70 0.66 0.55 0.54 0-59 Standard deviation 0.0025 0-0054 0.0026 0*0040 0.0024 0.0058 0.0082 0.0045 0.010 0.0035 0,0064 Coefficient of variation, per cent.0.51 0.88 0-59 0.61 0-63 1.06 1.18 0-68 1-82 0.64 1.07 * By thermometric procedure; titrant added a t 0.12 ml min-1. t Nominal value. $ Number of determinations. in solution in dimethylformamide for the thermometric titrations. All three of these inter- halogen compounds gave inferior titration graphs to that of iodine in the titration of pyridine, although all gave rises in temperature of the same order as that obtained with iodine. Although the iodimetric titration method is suitable for the assay of single compounds when interfering substances are absent, the method is obviously unsatisfactory for the determination of the total amount of a particular functional group in a complex mixture because different compounds combine with iodine in different molar ratios.However, Iodine reagent/ml (1 division = 0.5 ml) Fig. 6. Catalytic thermometric titration of organic bases, hydrazine derivatives and water with 0.01 and 0-005 M iodine reagents. a b C d e f Compound/mg . . A,O.54 B,O*24 C,0-28 D,O-14 E,2.0 E,l-O Titrant/M . . . . 0.01 0.01 0.01 0.005 0.01 0-005 Recorder/mV range 50 100 100 50 100 100 Compounds : A, isonicotinoylhydrazine ; B, tris(hydroxymethy1) methylamine; C, cc-picoline; D, pyridine; and E, waterFebruary, 19741 INDICATION I N NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART V 91 differences in reaction ratios make it possible to determine selectively the components of binary mixtures. A calibration graph for the analysis of a mixture of benzoylhydrazine and isonicotinoylhydrazine is shown in Fig.8. d I I 1 1 0.05~ iodine reagent (1 division = 0.5 mi) Fig. 7. Effect of monomer on end-point sharpness in blank titrations and in titrations of pyridine with 0.05 M iodine reagent. a, b and c, blank titrations (1 ml of dimethylformamide) ; d, e and f, titrations of pyridine (0.01 mmol). Monomers: a and d, ethyl vinyl ether; b and e, n-butyl vinyl ether; and c and f, isobutyl vinyl ether The results of titrations carried out with organic bases suggest that the number of iodine atoms that combine with one molecule of the base can be used as a measure of the strength of the base in the solvent used. In addition, the widely differing reactivities of the various compounds examined should make it possible to use the iodimetric titration in order to elucidate the structure of more complex heterocyclic nitrogen compounds and hydrazine derivatives. With bases, such a procedure for investigation of structure could be used in conjunction with that proposed in Part L5 t 5 0-25 0 __-___----------------- Blank titration 0.8 0.6 0.4 0.2 o 0.025~ reagent I/ml 0.2 0.4 0.6 0.8 I 0.025~ reagent Il/ml Fig.8. Calibration graph for the determination of benzoyl- hydrazine and isonicotinoylhydrazine in binary mixtures by catalytic thermometric titration with 0.05 M iodine reagent. Reagent I, isonicotinoylhydrazine in dimethylformamide ; reagent 11, benzoyl- hydrazine in dimethylformamide92 GREENHOW AND SPENCER The fact that, for many compounds, this iodimetric method gives results which indicate that iodine combines with the titrand in fractional molar amounts should not detract from its value as an analytical method. The requirements of reproducibility of results and linearity of calibration graphs can be met. Fisons Limited, Agrochemical Division, are thanked for gifts of chemicals and Mr. S. F. George is thanked for the construction of apparatus. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. Note-References 5, 7 and 9 are to Parts I, I11 and I1 of this series, respectively. Prescott, A. B., and Trowbridge, P. F., J . Amer. Chem. SOL, 1895, 17, 859, Coffey, S., Editor, “Rodd’s Chemistry of the Carbon Compounds,” Second Edition, Volume 1, Cheronis, N. D., and Ma, T. S., “Organic Functional Group Analysis by Micro and Semirnicro Siggia, S., Analyt. Chem., 1948, 20, 762. Greenhow, E. J., and Spencer, L. E., Analyst, 1973, 98, 81. Greenhow, E. J., Chew. G. Ind., 1973, 697. Greenhow, E. J., and Spencer, L. E., Analyst, 1973, 98, 98. Dixon, J. P., “Modern Methods of Organic Microanalysis,” Van Nostrand Co. Ltd., London, Greenhow, E. J., and Spencer, L. E., Analyst, 1973, 98, 90. Part B, Elsevier Publishing Company, London, 1965, p. 128. Methods,” Interscience Publishers, New York, 1964, p. 289. 1968, p. 211. Received July 19th, 1973 Accepted August 17th, 1973