2388 GREEN AND WOODHEAD: ANILINE-BLACK BNDCCXLIII.-Ariiline-blacl% and A llied Compoimds. Part I.By ARTHUR GEORGE GREEN and ARTHUR EDMUND WOODHEAD.ALTHOUGH the recent researches of Willstiitter and his pupils(Willstatter and Maore, Ber., 1907, 40, 2665; 1. SOC. Dyers, 1908,24, 4; Willstatter and Dorogi, Ber., 1909, 42, 2147, 4118) haveadded much of value to our knowledge of the complex oxidationproducts of aniline, the constitution of aniline-black and of itsintermediate products still cannot be regarded as completelyelucidated. The view advanced by Willstatter, that these com-pounds are all to be regarded as indamine-like derivatives of theeight-nucleal chain compound (leucoemeraldine) :NH NH NH NH/\/\/\ /’\/\/\ /\/\/\ /\/\/\I I I I I I I I I l l 1\/ \/\dH\/ \/\i& v\/,J O N E r z -will scarcely gain acceptance without further evidence.AsBucherer has pointed out, it might a priori be expected that sub-stances of such a type would exhibit a high degree of instability,and would readily decompose into simpler compounds under theinfluence of acids, etc.Amongst other arguments in support of the chain structure,Willstatter has shown that the qua.ntitative conversion into p-benz+quinone is only compatible with the existence of di-para-connexions,and is entirely opposed to an azine structure, such as that suggestedby Bucherer (Bey., 1909, 42, 2931):6 6 H, m 5 c P 5I n respect to the validity of t.his argument, it is, however, necessaryto point out that a sharp distinction must be made between thALLIED COMPOUNDS.PART I. 2389primary oxidation products of aniline (emeraldine, nigraniline, etc.)and the condensation products of these with aniline (“ ungreenableaniline-black ’7, which latter alone can be properly regarded as trueaniline-black. Willstatter’s experiments refer only to the formerclass of compounds, and it yet remains to be shown what yield ofp-benzoquinone is obtainable from the latter. It is quite con-ceivable, and in fact probable, that whilst the former possess adi-para chain or ring structure, the “ ungreenable aniline-black,”that is, true anilincblack, is an azine (Green, The Chemical Tech-nology of Aniline-black, 7th Internat. Congress of AppliedChemistry, London, 1909; J . SOC. Dyers, 1909, 25, 188).Only the“ ungreenable aniline-black ” can be correctly regarded as a highlystable compound ; the primary oxidation products probably owemuch of their apparent stability to their insolubility in water andaqueous solvents, for when dissolved in pyridine, etc., they exhibita much greater tendency to undergo change.The view held by Willstitter that ‘‘ ungreenable aniline-black ”is a compound of the same type as the primary oxidation products(that is, contains an eight-nucleal chain, and only differs from theprimary products in the degree of oxidation and the replacementof the terminal N H by 0), is opposed, in our opinion, to theexperimental facts. Were this view correct, the behaviour withsulphurous acid of the two oxidation stages he describes should bethe same, that is to say, both compounds should be reduced to thegreen monoquinonoid stage, and by the application of a, strongerreducing agent all should be reduced to the mother substance, thatis, to the oxygen analogues of leucoemeraldine :NH NH NH NHFurthermore, this reduction-product, like leucoemeraldine itself,would certainly be a tolerably stable substance, giving, on airoxidation, only the lowest quinonoid stage, and requiring theapplication of a strong oxidising agent to reconvert it into theoriginal tri- or tetra-quinonoid compound.These properties are notexhibited either by the preparations described by Willstatter as“ hydrolysed triquinonoid and tetraquinonoid blacks,” or by the“ ungreenable aniline-black ” produced on the fibre.The latter isnot reduced at all by sulphurous acid, and by stronger reducingagents, such as hyposulphites, it is converted into a leuco-compoundwhich is rapidly re-oxidised by air to the original “black,” andthat apparently without passing through any lower stage ofoxidation. Moreover, the facts known respecting the conditions o2390 GREEN AND WOODHEAD : ANILINE-BLACK ANDformation of ‘‘ ungreenable aniline-black ” clearly show that itcannot be a product of further oxidation alone, but is a con-densat.ion product with aniline of a different type to the simpleroxidation products from which it is formed (Green, Zoc. c i t . ) .I n order to throw more light on this complicated subject, it hasappeared to us necessary to obtain, in the first instance, furtherevidence for the molecular weight and constitution of the primaryoxidation products (emeraldine and nigraniline), and we haveattempted to do this by determining, on the one hand, the quantityof hydrogen required to reduce these products to Ieucoemeraldine,and, on the other, the quantity of oxygen necessary to oxidise eachstage into the next.The data obtained in this manner, combinedwith the fact that we have been able to recognise four distinctstages of oxidation of leucoemeraldine, support Willstatter’s viewof an eight-nucleal molecule, but do not agree with the constitutionassigned by Willstatter and Dorogi to the compounds they prepared.Assuming the correctness of the eight-nucleal structure for theprimary oxidation products, it still remains an undecided questionwhether the aniline residues are to be regarded as united in anopen or in a closed chain, but without attempting to decide thispoint we shall make use of the open-chain formulz to expressprovisionally the analytical results.The constitution of ‘ I ungreen-able anilineblack” we reserve for discussion in a later com-munication.Before proceeding to a consideration of the results obtained, it isdesirable to attempt to clear up some of the existing confusionregarding the various oxidation products of aniline and theirnomenclature, Much of the obscurity in this subject arises fromthe fact that no criterion of purity has hitherto existed, and thatthe products obtained have been doubtless largely mixtures.Unsuitable nomenclature has still further added to the confusion.Thus the name “ emeraldine,” which properly belongs to the firstacid-oxidation product of aniline-a violet-blue base giving greensalts, and well known to dyers of aniline-black-has been transferredby Willstatter and Moore to an entirely different compound, namely,the blue imide obtained by polymerisation of phenylquinonedi-imide,which was apparently first mistaken for emeraldine by Caro.Onthe other hand, for the true emeraldine, originally so-called byCrace-Calvert and Lowe, the name ‘‘ triquinonoid aniline-black ” isnow proposed by Willstatter and Dorogi, although emeraldine isneither black nor (as will be shown later) is it triquinonoid. I njustification for this confusing and unnecessary transfer of names,Willstatter and Dorogi advance the incomprehensible plea that“ technisches Emeraldine langst nicht mehr existirt.ALLIED COMPOUNDS.PART I. 2391The various oxidation products which have been described underthe name of aniline-black hy the earlier authors (Muller, Nietzki,Kayser, Guyard, etc.) are lacking in any criterion of purity orindividuality beyond that furnished by elementary analysis, whichin this case is quite inconclusive and valueless. The discovery thatthe primary oxidation products (emeraldine and nigraniline bases)are readily soluble in somewhat diluted organic acids, such as 80 percent. acetic acid and 60 per cent, formic acid (the former basegiving a green solution, and the latter a blue), whilst the highercondensation products are insoluble in these solvents, 1ia.s providedus with a valuable means for diagnosis and separation, by means ofwhich we have been able to show that all the above-mentionedso-called “ aniline-blacks ” consist, mainly of emeraldine andnigraniline mixed with varying proportions of higher condensationproducts. These I‘ blacks ” prepared in substance therefore do notproperly correspond with the aniline-black produced on the fibre,since in the latter case the higher condensation products are eitherexclusively present (ungreenable blacks) or largely predominate(greenable blacks).In order to simplify the nomenclature, we propose that the term“ aniline-black ” should be restricted to the higher condensationproducts (ungreenable black), whilst the original names “ emerald-ine ” and “ nigraniline ” should be retained for the primaryoxidation products.As, however, there is a stage of oxidation belowemeraldine and one above nigraniline, we propose for these thenames “ protoemeraldine ” and “ pernigraniline.” All four sub-stances, protoemeraldine, emeraldine, nigraniline, and pernigraniline,are quinonoid derivatives of the same parent substance, to whichwe have given the name “ leucoemeraldine.” Into this compoundthey are all converted on reduction, and from i t they can all beproduced by oxidation. At present the protoemeraldine stage hasonly been obtained in the o-toluidine series, whilst pernigranilineis too unstable to isolate in a dry state.Emeraldine.This compound is the first clearly defined stage in the oxidationof aniline in an acid medium, whatever the oxidising agent employed.When a chlorate is used, the reaction tends in part, to at onceproceed further with production of more or less nigraniline, butwith hydrogen peroxide, if not used in excess, the oxidation stopsat the emeraldine stage.If the reaction is effected in the cold andin the presence of an excess of acid, emeraldine and nigranilineare nearly the sole products, but if the mixture is neutral or onlyslightly acid, a certain quantity of condensation products (ungreen2392 GREEN AND WOODHEAD : ANILINE-BLACK ANDable black) is also produced. An excess of acid is therefore anecessary condition for preparing eineraldine in a pure state.Asthe result of a series of experiments, proportions corresponding with1 mol. of aniline hydrochloride to 1.33 mols. of oxygen and 1 mol.of hydrochloric acid were found the most suitable.Emeraldine is also produced by the further oxidation of the blueimide, C6H,-NH*C,H4*NH*C,H4*N:C,H,:NH, of Willstatter andMoore (termed ‘ I emeraldine ” by these authors).I. A solution of 100 grams of aniline hydrochloride, 42 grams ofsodium chlorate, and 46.5 C.C. of hydrochloric acid (33 per cent. HCl)in 1800 C.C. of water, to which 2 drops of syrupy vanadium chlorideare added, is kept in the cold for from two to three days. Theprecipitate is then collected, washed thoroughly with water, basifiedby mixing the paste with dilute ammonia in a mortar, finally washedwith alcohol and with water, and dried at 3 5 4 0 O .The productthus obtained contains a varying amount of nigraniline, which maybe readily converted into emeraldine by warming the precipitatewith dilute hydrochloric acid before basifying. Pure emeraldinemay also be obtained by dissolving the crude base in 50 parts of80 per cent. acetic acid, filtering from any insoluble matter, re-precipitating by addition of dilute hydrochloric acid, collecting thehydrochloride, and finally basifying the precipitate wit-h ammonia.During this process the nigraniline present is converted intoemeraldine.11. A solution of 50 grams of aniline hydrochloride in 24 litresof water, to which is added 135 C.C. of hydrochloric acid (33 percent.HCl), 380 C.C. of hydrogen peroxide solution (4.6 per cent.),and 0.5 gram of ferrous sulphate, is kept in the cold for twenty-fourhours. The precipitated emeraldine is collected, washed, andbasified with ammonia.111. Ten grams of paminodiphenylamine are dissolved togetherwith 27 C.C. of hydrochloric acid (33 per cent. HC1) in 1 litre ofwater. After cooling t o 0-5O by addition of ice, 78 C.C. of hydrogenperoxide (4.7 per cent.), followed by 0.1 gram ferrous sulphate, areadded. The hydrogen peroxide used wits rather more than twicethe quantity required to convert the aminodiphenylamine intoWillstatter and Moore’s blue imide. On adding the iron salt, avoluminous indigo-blue precipitate of the imide was first produced,which, after about twelve to twenty-four hours, slowly lost its bluecolour and became green, while the excess of peroxide disappearedand an odour of p-benzoquinone was apparent.The mixture waswarmed on the water-bath, and the precipitate collected, washed,and basified with ammonia.When prepared by either of these methods, the emeraldine basALLIED COMPOUNDS. PART I. 2393forms an indigo-blue powder, which, when purified by the aceticacid method, has a bronzy lustre. When dried at a low temperatureit retains a remarkably large amount of water (about 30 per cent.).It is insoluble in alcohol, benzene, chloroform, etc., but dissolvesreadily in cold pyridine, giving a bright blue solution. This solutionis, however, very unstable, for in a short time the greater part ofthe product separates out again a.s a colloidal precipitate.Thisprecipitate consists of a condensation product of quite differentproperties to the original emeraldine. In concentrated sulphuricacid, emeraldine dissolves with a reddish-violet colour, and onaddition of water a bright green precipitate of the sulphate isobtained. Towards acetic and formic acids the behaviour ofemeraldine and nigraniline is very remarkable. These bases areinsoluble in glacial acetic acid or in concentrated formic acid, andare also insoluble in these acids when fairly dilute, but in acids ofmedium concentration, that is, in acetic acid of about 80 per cent. orin formic acid of about 60 per cent., they dissolve readily. Thesolutions obtained with emeraldine are yellowish-green, and givea green precipitate on the addition of mineral acids or salts.Bymeans of such a solution, the various stages of oxidation can bevery effectively demonstrated, for on addition of a very dilutesolution of chromic acid the green colour of the solution firstchanges to pure blue (nigraniline), and then, as more oxidisingagent is added, to violet (pernigraniline), finally giving a violetprecipitate (pernigraniline chromate). I f to the violet solution ofthe pernigraniline a very weak solution of sodium hydrogen sulphiteis added, these colour changes occur in the opposite direction,namely, from violet to blue, and from blue to green. Strongerreducing agents, such as phenylhydrazine, sodium hyposulphite, ortitanium trichloride, convert emeraldine into leucoemeraldine.I n order to determine the quantity of hydrogen required forconversion of emeraldine into leucoemeraldine, the acetic acidsolution was titrated with titanium trichloride according to Enecht’smethod, the analysis being carried out as follows.One gram ofemeraldine in fine powder is weighed into a 250 C.C. flask containing50 C.C. of water, and well shaken t o prevent any of the powderagglomerating into lumps. Glacial acetic acid is then added untilthe flask is about threequarters full, the contents well shaken, andheated on the water-bath for fifteen minutes t o about 90° toensure conversion of all nigraniline present into emeraldine. Thosolution is then cooled, and made up to the mark with glacial aceticacid.For each titration, 25 C.C. of this solution (=0-1 gram ofsubstance) are transferred, by means of a pipette, to a conical flask,and mixed with 25 C.C. of water and a measured excess of titaniumVOL. XCVII. 7 2394 GREEN AND WOODHEAD : ANILINE-BLACK ANDtrichloride, the strength of which is re-determined each day. Themixture is kept in the cold for ten to fifteen minutes, air beingexcluded by a slow stream of carbon dioxide. At the end of thistime the solution is quickly filtered from the precipitated leuceemeraldine, employing a funnel and filter paper enclosed in a vesselfilled with carbon dioxide. An aliquot portion of the whole (50 c.c.)is then transferred to another flask also containing carbon dioxide,and at once titrated with a standard ferric alum solution, employingammonium thiocyanate as indicator.I n calculating the results, thepercentage of water, chlorine, and ash is allowed for, and a furthersmall correction, determined by parallel blank experiments madeunder exactly the same conditions, is introduced for the loss oftitanium trichloride oxidised by air during the operation. The firstpreparation analysed (obtained by method I) contained 31.9 percent. of water, 1-1 per cent. of chlorine, and 0.1 per cent. of ash.The following results were obtained :VOl. GfTiCI,No. ofexperinienrun in,.t. C.C.1 252 253 254 255 256 257 258 25Vol. ofTiC1,unoxidised,13-7014-1514-1513'2313.6513'5513-4713-47c. c.Vol.ofTiUI,oxidisedby air,1.770.920.921-301'341 '331 *291 -29C . C.Hydrogenvalue of1 litreTiCI,,gram.0.03740'03660.03660-03580.03580.03580 03580.0358Mean .........Percentageof hydrogenon puredryemeraldhe.0.5330.5430.5430.5800.5360-5420.5450.5450.543--A second series of estimations was made with a larger excess oftitanium trichloride and another preparation of emeraldine con-taining 30'65 per cent. of water, 1.0 per cent. of chlorine, and 0.1per cent,. of ash. Using 0.1 gram for each titration, the followingresults were obtained :Vol. of Vol. ofTiCI, TiC1, un-No. of run ill, oxidised,experinleu t. c. c. c. c.1 50 40.692 50 4 0 5 93 50 40'804 50 40'69Vol.ofTiCI,oxidisedby air,0-870.870.880'87c. c.Hydrogen Percentagevalue of of hydrogen1 litre on puregra 111. emeraldine.0.0442 0.5470'0442 05530'0442 05400'0442 0.547TiCI,, dryMean ......... 0.547Figures of the same order were also obtained by direct titrationof the acetic acid solution with titanium trichloride, although, owinALLIED COMPOUNDS. PART I, 2395to the uncertain end-point, the results were not as trustworthy asthose obtained by the indirect method.The mean value of the two series of determinations was 0.545gram of hydrogen for 100 grams of pure dry emeraldine.A diquinonoid compound of the formula :NH N kI N N/\/\/\ /\/\/’\ /\/\/’\ /\/\/\I I I I I I I I I I 1 1 I I I I:NH\/ \/\dHV ‘\A/<\/ \/>/\/ \/would require 0.555 per cent.of hydrogen for complete reduction tothe leuco-compound.I n order to estimate the, quantity of oxygen consumed in theconversion of emeraldine into nigraniline, two methods have beenadopted. The first consists in titrating an acetic acid solution ofemeraldine with a standard solution of chromic acid until the pureblue colour of the nigraniline is reached. The second consists inseparately titrating emeraldine and nigraniline until the violetpernigraniline chromate is completely precipitated. Deduction ofthe quantity of chromic acid required to reach this point fornigraniline from the quantity required to reach the same point foremeraldine gives the quantity consumed in oxidising emeraldine intonigraniline. Owing to the more definite end-point, the lattermethod is the more trustworthy.I.Twenty-five C.C. of emeraldine solution, containing 0.1 gram ofsubstance dissolved in 80 per cent. acetic acid, were diluted with 25C.C. of water, and titrated with a solution of chromic acid containing3.52 grams of chromium trioxide per litre (equal to 0.845 gram ofoxygen per litre). The emeraldine employed contained 31.9 percent. of water, 1.1 per cent. of chlorine, and 0.1 per cent. of ash and1.5 C.C. of chromic acid (several experiments) were required to givea pure blue colour. Correcting for contents of water, chlorine, andash, this is equivalent to a consumption of 1.9 grams of oxygenper 100 grams of pure dry emeraldine for oxidation to nigraniline.11. (a) Twenty-five C.C.of emeraldine solution, containing 0.1 gramof substance dissolved in 80 per cent. acetic acid, were diluted with25 C.C. of water, and titrated with a solution of chromic acid con-taining 0.704 gram of chromium trioxide per litre (equal to 0.169gram of oxygen per litre) until the precipitation of the violetpernigraniline chromate was complete, and no further change ofcolour took place. The emeraldine employed contained 30-65 percent. of water, 1 per cent. of chlorine, and 0.1 per cent, of ash.7 ~ 2396 GREEN AND WOODHEAD : ANILINE-BLACK ANDWeight of Vol. of ClO,No. of el ileraldiii e, required,experiment. gram. c. c .1 0 '1 24 -52 0.1 25 -03 0.1 25 *O4 0-1 24.5Mean,. . , , * . . IPerceiit:Lgo ofoxygen 011pnre dryemeraldine.6.076 '196-196.07,.6'13-( b ) A weighed quantity of nigraniline (preparation see later) wasadded in a state of fine powder to 5 C.C. of water. The whole wascooled in ice, 20 C.C. of glacial acetic acid added, the mixture shakenuntil dissolved, and then a t once titraked with chromic acid asabove. The nigraniline employed contained 11.28 per cent. ofwater, 1.12 per cent. of chlorine, and 1.3 per cent. of ash:Weight of Vol. of CrO,No. of nigraniline, required,1 0.0950 19-52 0.0983 20'03 0'1257 25 -04 0.1017 21.0cxperimen t. gram. c. c.Mean ......Percentage ofoxygen onpure drynigran iliiie.4'023.983'894 '04,.. 3.98-Deducting 3-98 from 6-13 gives 2.15 as t.he percentage of oxygenrequired to oxidise pure dry emeraldine into nigraniline.Ifemeraldine has the above formula, it would require, theoretically,2-20 per cent. of oxygen for the removal of two hydrogen atoms,that is, to introduce one quinonoid group.Nigraniline.The best method for the preparation of nigraniline in substancewas found to be the oxidation of emeraldine base (or the mixtureof emeraldine and nigraniline obtained by the chlorate oxidation),using an excess of hydrogen peroxide in an ammoniacal solution.For instance, the precipitate obtained by oxidising 40 grams ofaniline hydrochloride and 18.6 C.C. of hydrochloric acid with 16.8grams of sodium chlorate in presence of vanadium, as alreadydescribed, is basified with ammonia, and the washed product,without being dried, is evenly suspended in 6 litres of water, towhich 400 C.C.of hydrogen peroxide (3 per cent.) and 40 C.C. ofconcentrated ammonia are added. After keeping overnight, theprecipitate is collected, washed well, and dried at 35O. The productcontained 11.28 per cent. of water, 1.12 per cent. of chlorine, and1.30 per cent. of ashALLIED COMPOUNDS. PART I. 2397Nigraniline base forms a bluish-black powder with a bronzy lustre.Like emeraldine, it is insoluble in most solvents, but dissolves incold pyridine with a bright blue colour. The salts are blue, notdark green as stated in the literature. This error arises from thefact that nigraniline salts are very unstable, and both in substanceand on the fibre are readily converted into salts of emeraldine. Thechange takes place slowly in the cold, but more rapidly on heating,and is accompanied by the production of p-benzoquinone.Onepart of the nigraniline is oxidised to p-benzoquinone, whilst anotherpart is reduced to emeraldine, a fact which affords an explanationof the well-known “greening” of certain blacks on the fibre whenexposed to an acid atmosphere. Similarly, when nigraniline isdissolved in concentrated sulphuric acid, it gives a violet solutionof rather bluer shade than t>hat of emeraldine, but on pouring intowater, decomposition occurs, and a bright green precipitate ofemeraldine sulphate is produced. Nigraniline dissolves readily andcompletely in cold 80 per cent. acetic acid or in 60 per cent.formicacid, giving pure deep blue solutions. These solutions, on warming,quickly change in colour t o the green of the emeraldine salt. I ncontrast to the instability of the salts, nigraniline base is quitestable.In performing the quantitative reduction of nigraniline, it isessential for the above reasons to avoid all heating in making thesolution, and to effect the reduction as rapidly its possible. Theoperation is therefore carried out as follows. A weighed quantity ofnigraniline (about 0.1 gram), which must be very finely powderedto ensure quick and complete solution, is suspended in 5 C.C. ofwater contained in a small flask. The flask is then cooled in icefor ten minutes, 20 C.C. of glacial acetic acid added, and the mixtureshaken for half a minute, by which time the substance should havedissolved completely.Before the addition of the acetic acid, theair in the flask is expelled by carbon dioxide. The titanium tri-chloride solution is then added, and the titration effected in thesame manner as with emeraldine:Weigli t ofnigranilineNo. of taken,experiment. gram.1 0.10092 0.06733 0-10894 0.13205 0.11986 0’1108Vol. ofTiC1, run in(1 litre=0.0307 gramof hydrogen),40404050505 0c. c.Vol. ofTiCI, leftunoxidised,17.323.8515’6220.4723-3824.35c. c.Vol. ofTiCl,oxidisedby air,0.871.200-780.630 *720 *75C.C.Percentage ofhydrogen onpure drynigraniline.0.7710,7910.7720.7810.7700’801Mean ...... ... 0.782398 GREEN AND WOODHEAD : ANILINE-BLACK ANDAnothersolution (1results :No. ofexperiment.78910series of titrations made with a stronger titaniumlitre = 0.0442 gram of hydrogen) gave the followingWeight ofnigranilinetaken,gram.0‘13860*09000*10900.1035VOl. ofTiCI, run in(1 litre =0.0307 grainof hydrogen),50505050c. c.Vol. ofTiCl, leftunoxidised,27 -9835-0632.1032.95e. c.Vol. ofTiCl,oxiciisedby air,0.510.630.580’60c. c.Percentage ofhydrogen onpure drynigraniline.0,7970.8160.8160’816Mean.. .... ... 0.811A triquinonoid compound of the formula:NH N N N/\/ \/\ /\/\/\ /\/\/\ /\,A/\1 1 1 1 1 1 ! 1 1 l 1 1 1 I I.Nwould require 0.835 per cent.of hydrogen for complete reductiont o leucoemeraldine. This formula is also supported by the oxidationnumbers given under emeraldine.Although the above formula is the same as that given byWillstatter and Dorogi to the preparation which they term “tri-quinonoid aniline-black,” yet the compound described and analysedby them can scarcely be identical with nigraniline, for the propertiesdo not correspond. If these authors originally had nigraniline inhand, it must have suffered conversion into emeraldine, and probablyinto further decomposition products by the process of purificationemployed.Pe rniqranitin e.N N N NWhen a, solution of emeraIdine or nigraniline in acetic or formicacid is treated with an excess of a powerful oxidising agent, suchas chromic acid or ammonium persulphate, the oxidation proceedsbeyond the nigraniline stage, giving rise to a violet precipitate,which, on basifying with ammonia, yields a purple-brown compound,‘ I pernigraniline.” This substance is exceedingly unstable, decom-posing slowly on drying, or even if kept in the paste form, withreproduction of nigraniline and formation of other products.Thisdecomposition occurs still more rapidly in the presence of acids,following a, similar course to nigraniline, which, together withp-benzoquinone, is first formed. The change is brought about bya few drops of dilute hydrochloric acid, and also more slowly byacetic acid. Reducing agentfi, if applied at once, convert perALLIED COMPOUNDS. PART I. 2399nigraniline first into nigraniline, then into emeraldine, and finallyinto leucoemeraldine. The base is soluble in pyridine, with a purplecolour, and apparently undergoes decomposition in this solvent inthe same manner as do emeraldine and nigraniline.I n con-centrated sulphuric acid, it dissolves with a bluish-violet colour.On pouring this solution into water, a green precipitate of emeraldinesulphate is produced.On account of its instability, pernigraniline cannot be obtainedpure in the dry state; an almost complete reversion to nigranilineoccurs during drying, An attempt was therefore made to submitit, without drying, to analysis by reduction, employing a paste whichcontained 8-45 per cent. of dry product. This was prepared asfollows.Five grams of tho mixture of emeraldine and nigranilinebase obtained by the chlornte method were dissolved in 500 C.C. of80 per cent. acetic acid. To the icecold solution was added 5 gramsof ammonium persulphate dissolved in a little water, when a violetprecipitate at once separated. The whole was then immediatelystirred into an excess of dilute ammonia mixed with crushed ice,the temperature being kept as low as possible, After adding alittle salt, the precipitate was collected, washed with several litresof water, and brought to a uniform consistency, in which the per-centage of water was estimated. The following results were obtainedon analysis:Weight ofpernipanilinepaste (8'45No. of per cent.)experiment. grams.1 0.95652 1-17823 0'89004 1.8010Vol. of TiCI,run in (1 litre= 0.0507 gramof hydrogen),50505050c. c.Vol.ofTiCl, leftunoxidised,34'731 -836 '424.9c. c.VOl. ofTiCI,oxidisedby air,0-280-250.290 '20c. c.Percentageo f hydrogenon dry per-nigraniline.0.9490.9140.89607330A tetraquinonoid compound of the above constitution wouldrequire for reduction to leucoemeraldine 1.1 1 per cent. of hydrogen.It will therefore be seen that, whilst the first titration gives a valueapproaching that required by this formula, there is a steadydiminution in the consumption of hydrogen in the later analyses.The last titration, which was made after the paste had been kepta day, gives a hydrogen value almost corresponding with that ofnigraniline (theory, 0.835 per cent.).The above formula for pernigraniline is also supported by thefigures given on p.2396 for the consumption of chromic acid requiredto oxidise emeraldine and nigraniline to pernigraniline chromate.Thus, calculating the whole chromic acid as oxygen, the results are :C43H34N8 + $30, requires, Oxygen consumed,6.13per cent. per cent.From emeraldine.. . , . . . , , 5 -96 ,, nigraniliiie .. . . . . 3-98 3'72400 GREEN AND WOODIIEAD : ANILINE-BLACK ANDIt will be seen that the above formula for pernigraniline is thesame as tbat assigned by Willstiitter and Dorogi to the preparationswhich they call “ tetraquinonoid . aniline-black.” The greatinstability of pernigraniline is, however, entirely inconsistent withthe assumption that these products are identical, since the treatmentto which Willstatter and Dorogi’s preparations were subjected wouldhave completely decomposed pernigraniline, and even the dryingalone, without t,reatment with acid, would have converted it intonigraniline.L euco emerddine.NH NH NH NHA/\/\ /\/\/\ AA/\ /\/\/\1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1\/ \/>/\/ \A*&/ \/\NJH\/ \/*l1?This product is readily prepared by reducing either emeraldineor nigraniline with a strong reducing agent.For instance, themixture of emeraldine and nigraniline bases obtained by the chlorateoxidation was moistened with alcohol in a mortar, and then groundto a paste with a concentrated solution of sodium hyposulphite anda little ammonia.The precipitate was collected, washed, and driedin a vacuum.A better method consists in moistening the dry base with puredry ether, and grinding the paste with an equal weight of phenyl-hydrazine. It is then thrown on a filter, and washed with dryether until the excess of phenylhydrazine is removed, after whichthe product is dried quickly on a porous plate.Leucoemeraldine forms a pale brown, amorphous powder, probablycolourless when pure, which does not melt below 350O. It is fairlystable when dry, but when exposed to air in a damp st-ate it becomesblue. It is insoluble in most solvenk, but dissolves to a slightextent in pyridine. In 80 per cent. acetic acid or in 60 per cent.formic acid, it is sparingly soluble.The constitution assigned to leucoemeraldine above is supportedby the fact that four atoms of hydrogen are required for itsformation from emeraldine, and six atoms for its formation fromnigraniline.Willstatter and Dorogi’s Blacks.I n order to ascertain how far the products examined by theseauthors, and termed “ triquinonoid aniline-black ” and “ tetra-quinonoid aniline-black,” compare in properties with the foregoingcompounds, we have prepared them by following exactly the pre-scriptions given.The properties of the products we obtained aregiven in the following tableALLIED COMPOUNDS. PART I. 2401Prodnc t.I’ersulpliate Black.(W. & D.)Richroniate Black.(W. & D.)Chlorate Black :triquinonoid, 6hours. (W. & D.)triquinonoid, 23hours.(W. & D.)tetraquinonoid, 6hours. (W. & D. )Chlordte Black :tetraquinonoid,22 hours.(We& D.)Clilorate Black :Chlorate Black :80 per cent. aceticacid.Considerable por-tion soluble withb r i g h t bluish-green colonr.As above.Small part solublewithdullgreenishcolour.Trace soluble withd u l l g r e e n i s hcolour.Small part solublewith dull greenishcolour.Sparingly solublew i t h greeniskcolour.60 Per cent. formic !acid. Ipyridine,Partly soluble with I Considerable por-b r i g h t green tion soluble withcolour. ~ deep blue colour.1As above. i As above.Nearly insoluble. Trace only solublewith pale blue 1 colour.Insoluble.Insoluble.Very sparinglysoluble.Very s p a r i n g l ysoluble with palebluc colonr.As above.As above,It will thus be seen that these products differ entirely from theemeraldine, nigraniline, and pernigraniline described above.Theyappear to be mixtures contqining emeraldine, together with furthercondensation products. Three of them were submitted to successiveextractions with cold 80 per cent. acetic acid until nothing furtherdissolved.Chlorate Black :The following were the results obtained :Persulpliate Black Bichroinate Black triquinonoid(W. & D.), (W. & D.), (W. & D.),per cent. per cent. per cent.Soluble poi tion . . . . , , 51-5 60’0 80.0Insolnble portion . . . 48.5 40’0 20 .oOxidation of o-Toluidine.It has long been known to technologists that o-toluidine, whenoxidised on the fibre, gives rise to a black which is not so brilliantas aniline-black, but which has less tendency to ((green.” Noattempt has apparently been made to prepare this dye or its inter-mediate compounds in substance.We have found that under the same conditions its employed foraniline the oxidation proceeds in an analogous manner, givingcorresponding products.It appears, however, that the pnmaryoxidation products are rather less stable than in the aniline series2402 GREEX AND WOODHEAD : ANlLlNE-BLACK ANDbeing more prone to undergo polymerisation, and that the higherquinonoid products are less easily formed, and more readily revertto the lower. The best results were obtained by conducting theoxidation without any excess of mineral acid.Thus, 33 grams ofo-toluidine and 34 grams of hydrochloric acid (33 per cent.) weredissolved in 700 C.C. of water, with the addition of 16.8 grams ofsodium chlorate and 2 drops of syrupy vanadium chloride. Afterbeing kept for three days at the ordinary temperature, the greenish-blue precipitate was collected, washed with water, basified withammonia, and then repeatedly extracted with 90 per cent. alcoholin order to remove a soluble by-product ( ? homologue of Willstatter'sblue imide). It was then dried a t 30-35O. The product is aviolet-blue powder of indiplike appearance. It is insoluble inmost solvents, but dissolves readily in pyridine with a blue colour,and in 80 per cent. acetic acid or 60 per cent. formic acid with adull yellowish-green colour.It contains 4.6 per cent. of waterand 2.0 per cent. of chlorine.The analysis by reduction wils effected in the same manner asemployed for emeraldine.Vol. of TiCl, HydrogenVol. of TiCI, Vol. of TiCl, oxidised by value of 1 PercentageNo. of run in, unoxidised, air, litre TiCl,, on pure dryexperimcn t. c. c. c. c. c. c. gram. substance.1 50 45'43 0.36 0.0506 02282 50 45-15 0.36 0-0506 0.2433 50 44'71 0.36 0-0506 0'2674 50 44'89 0.36 0.0506 0'2575 50 45'88 0-37 0.0506 0-20350 45'25 0.36 0.0506 0'238 60'239-Mean.. . . . . . . .A monoquinonoid compound of t,he constitution :Me N H Me N H Me NH Me N/\/\A /\A/\ /v\/\ /\A/\I I I I I I I I I I I I I I I I.NH.\/ \&y \M;\N&-\/ \M</<\/ \/-Alewould require 0.24 per cent.of hydrogen for reduction to theleuco-compound. It therefore appears that the product of theoxidation of o-toluidine is the protoemeraldine of this series.Another preparation in which an excess of acid was used in theoxidattion gave as the average consumption of hydrogen for reduction0.360 per cent. This preparation was therefore apparently amixture of the t oh-protoemeraldine with t olu-emeraldine.Attempts to oxidise tolu-protoemeraldine into a higher oxidationstage by means of hydrogen peroxide and ammonia, employing thesame conditions as those used for nigraniline, gave a negative result.The product still dissolved in acetic acid with st green colour, anALLIED COMPOUNDS. PART I. 2403afforded the same reduction figures as before. On the other hand,on a.ddition of chromic acid or persulphate t o the acetic acid solution,the colour first becomes blue and then violet, as in the aniline series.It therefore appears that the formation of the tolu-nigraniline doesnot take place with the same facility as with the lower homologue,a conclusion which is supported by the fact that no tolu-nigranilinewas ever produced in our experiments with the chlorate andvanadium oxidation.Oxidation of Other Amines.The oxidation of various primary amines was studied under thesame conditions as employed in the preparation of emeraldine.o-Chloroaniline gave emeraldine-like products ; m-chloroaniline gavenone. o-Anisidine underwent oxidation in a different direction,apparently through elimination of the methyl groups. Dimethyl-aniline remained unattacked.Con clusio?ts.1. There are four quinonoid stages derived from the parent com-pound leucoemeraldine.2. The minimum molecular weights of these primary oxidationproduct8 of aniline are in accordance with an eight-nucleal structure.3. The conversion of emeraldine into nigraniline consumes oneatom of oxygen.4. The conversion of emeraldine into pernigraniline consumes twoatoms of oxygen.5. The conversion of nigraniline into pernigraniline consumes oneatom of oxygen.6. The reduction of emeraldine to leucoemeraldine consumes fouratoms of hydrogen.7. The reduction of nigraniline to leucoemeraldine consumes sixatoms of hydrogen.8. The reduction of pernigraniline to leucoemeraldine consumeseight atoms of hydrogen.9. The reduction of tolu-protoemeraldine consumes two atoms ofhydrogen.10. None of these products are properly entitled to be consideredas aniline-black, but are intermediate products in the formationof the latter.DEPARTMENT OF TINCTORIAL CHEMISTRY,UNIVERSITY OF LEEDS