1550 MILLS AND HAMER THE CYANINE DYES. PaRT III. CLXX1.-The Ciyanine Dyes. Part III. The Con-stitutzon of Pinacyanol. By WILLIAM HOBSON MILLS and FRANCES MARY EAMER. ONE of the most valuable of the photographic sensitisers in common use is a substance patented in 1905 by the Farbwerke vorm. Meister Lucius & Bruning (Brit. Pat. 16227 of 1905; D.R.-P. 172118) and sold under the name of pinacyanol. The action of alkali on a hot alcoholic solution of a mixture of a quinoline and a quinaldine alkyl haloid brings about as is well known the development of an intense reddish-purple colour on account of the formation of an isocyanine. I f however form-aldehyde as well as alkali is added to the solution the colour produced is a beautiful deep blue and the substance to which this is due is a dye of the type of pinacyanol.Corresponding with the difference in colour these blue dyes sensitise much further into the red than the isocyanines. A large number of compounds of this class have been prepared and examined in this laboratory and the name carbocyanine has been proposed for them to provide a basis for their systematic nomenclature (Pope and Mills Phot. J., 1920 60 253). I n view of the practical importance of these dyes and of the interest attaching to the relationship between photo-semitisin MILLS AND HAMER THE CYANINE DYES. PART III. 1551 activity and struct,ure a definite knowledge of their constitution is much to be desired. Two structural formulae have previously been put forward but neither of them can be regarded as free from objection.0. Fischer ( J . p r . Chem. 1918 [ii] 98 204) has proposed formula I and Wise Adam Stewart and Lund ( J . Ind. Eng. Chem. 1919 11 460) suggest the constitution 11. /\ R I (1.1 (11.1 Fischer’s formula appears not to represent the composition of the dyes correctly. It contains one atom of carbon less than is indicated by our analytical results. It is also improbable that compounds of this structare would possess the intense colour of the car bocyanines. The formula suggeted by the American investigators represents the carbocyanines as dimethyl derivatives of the true cyanines. This does not accord with their photo-sensitising action nor does it agree with their behaviour on oxidation. The formula which our experiments have led us to regard as the most probable repre-sentation of the structure of the carbocyanines is 111.It is based I (111.) on the following facts and considerations. (1) The carbocyanines are quaternary ammonium salts evidently containing tlwo atoms of nitrogen and one equivalent of acid radicle in the molecule. A series of careful halogen determinations made on the dye obtained by treating quinaldine ethiodide with form-aldehyde and sodium hydroxide (1 1’-diethylcarbmyanine iodide), and on the corresponding bromide showed that the molecular weight of the iodide was 479 f 1. Two molecules of quinaldine ethiodide are clearly concerned in the production of one molecule of the dye but since it contains carbon hydrogen nitrogen and iodine only the maximum mole-cular weight it could possess if derived from two molecules o 1652 MILLS AND HAMER THE CYANME DYES.PART III. quinaldine ethiodide with the loss of hydrogen iodide would be 470. The observed molecular weight therefore shows that con-tsary to the view of 0. Fischer (Zoc. cit.) it must contain the residue of one molecule of formaldehydel. Bimple condensation with one molecule of f orinaldehyde would result in the addition of 12 units t o the molecular weight. The observed increase of about 10 units indicates that in addition to the elimination of hydrogen iodide and water hydrogen (probably 2 atoms) has been remo'ved by some process of oxidation. The probable reaction for the formation of the dye is therefore 2C,oH9N,C2H5X + CH20 = C,,H&,X + H,O + HI + 2 8 , and the formula C,,H,,N,X thus indicated is in excellent agree-ment with the analytical results.(2) Whilst the isocyanines are formed by condensation of one molecule of a quinoline alkyl iodide with one of a quinaldine alkyl iodide two molecules of a quinaldine alkyl iodide are necessary for the formation of a carbocyanine; a quino'line alkyl iodide i f present takes no1 direct part in the condensation. This fact was discolvered by 0. Fischer (Zoc. cit.) and also strongly suspected by the American investigators. It was similarly discovered in t'his laboratory through observing that' the compolund produced by the action of alkali and formaldehyde on a mixture of the ethiodides of quinoline and quinaldine was identical with that obtained from quinaldine ethiodide alone.The yield is however very much better in the former case and this suggested that possibly the additional amount of carbocyanine might be formed from one molecule of quinoline alkyl iodide two molecules of formaldehyde and one of quinaldine alkyl iodide. The action of alkali and formaldehyde on a mixture of p-tdu-quinaldine ethiodide and quinoline ethiodide was therefore investigated. The amount of sensitisw produced was about the same as from the corresponding mixture of quinaldine ethiodide and quinoline ethiodide and itl was found1 to be a homogeneous substance since, by extractioln with successive quantities of methyl alcohol it was divided into six fractions identical in properties and analysis showed that these consisted of the 1 1'-diethyl-6 6/-dimethylcarbo-cyanine iodide described by Pope and Mills (Zoc.cit.). The whole of the carbocyanine formed thus contained two p-toluquinaldine residues and the quinoline ethiodide did not contribute to the carbon skeleton of any portion of the dye produced. The behaviour of many other substituted quinaldine alkyl ioldides in the carbocyanine condensation has been examined in this labora-tory with similar results (Pope and Mills Zoc. cit.); thus fo MILLS AND HAMER TRE CYANINE DYES. PART 111. 1663 example from bromoquinaldine ethiodide and quinoline ethisdide, a dibrcmocarbocyanine iodide is formed. It therefore appears that the alkyl iodides of the quinoline bases can only take part in the carbocyanine condensation prosvided they contain a 2-methyl group and in this condensation two molecules of such an alkyl iodide and one of formaldehyde are concerned.(3) When a solution of diethylcarbocyanine bromide in dilute nitric acid is heated the dye is rapidly oxidised and the liquid, after becoming almost immediately bright orange-red is gradually decolorised the colour practically disappearing after about an hour's boiling. From the residue left after the nitric acid has been evaporated which consists of a mixture of highly soluble substances FL crystalline quaternary nitrate can be isolated. The composition of this nitrate together with its properties and the fact that it gives 1-ethyl-2-quinolone on oxidation with potassium ferricyanide shows it to be quinaldinic acid ethyl nitrate ( A ) . It is clearly derived from one of the quinaldine residues present in the pinacyanol molecule and the yield of analytically pure material isolated varied in four experiments from 89 to 93 per cent.of the theoretical. The production of this compound shows that piaacyanol cclntaihs the grouping IV. ( A * ) (IV. 1 (V.) Moreover that it is formed so smoothly and easily further indicates that this residue is united to the rest of the molecule by an ethylenic linking and thus that pinacyand cohtains the grouping V. The other main oxidation product or products are exceedingly soluble and have not yet been identified. The residue left after the removal of the quinaldinic acid) et,hyl nitrate was therefme further oxidised with alkaline ferricyahide ahd was found to give rise to 1 -ethyl-2-quinolone.* The weight of distilled colourless, crystalline product was 60 per cent.of the weight of ethylquinolone theoretically obtainable from one quinaldine residue in the pina-cyan01 originally taken. It1 was not quite pure (m. p. 50-54O with incipient softening a t 40° ; pure 1-ethyl-2-quinolone melts a t 53-55*5O) but analytically pure ethylquinolone was easily isolated from it and it was evident that far more quinolone had been pro-duced than could possibly have been derived from the 11 p0r cent. * The production of ethylquinolone by the oxidation of pinmyanol bg potassium feicyanide was observed by 0. Fischer (Zoc. cit.) 1554 MILLS AND HAMER THE CYANINE DYES. PART 111. of the first quinaldine residue unaccounted for as quinaldinic acid ethyl nitrate.It must therefore have been formed mainly from the second quinaldine residue present in pinacyanol. That this second quinaldine residue should be split off on oxidation as l-ethyl-2-quinolone shows that the quinoline nucleus contained in it must be attached to the rest of the molecule through the 2-position. More precise conclusions can scarcely be drawn from this fact for oxidation with alkaline ferricyanide is not fitted to decide more delicate points of constitution ; for example Decker and Remfry (Ber. 1905 38 2773) have shown that quinaldine alkyl iodides are converted by this reagent into the corresponding quinolones. The action of potassium permanganate on pinacyanol acetate in aqueous acetone solution a t Oo was therefore studied (compare Mills and Wishart# this vol.p. 579). The permanganate was added gradually and the end of the reaction was sharply marked by the persistence of the permanganate colour after a quantity corresponding with 4.8 atoms of oxygen to one molecule of pina-cyanol had been added. Oxidation under these conditions brought about the fission of the pinacyanol molecule with the production of 1 -ethyl-2-quinolone. The quantity of pure substance isolated' amounted to 79 per cent. of that theoretically obtainable from one quinaldine residue. The other product was exceedingly soluble and showed the behaviour of a quaternary salt. When boiled with dilute nitric acid it gave quinaldinic acid ethyl nitrate but the oxidation did not proceed smoothly and the quantity of the nitrate isolated was only 25 per cent.of the theoretical yield from half the pinacyanol molecule. These observations especially when con-sidered in relationship to the action of potassium permanganate on dimethylisocyanine acetate (Mills and Wishart Zoc. c i t . ) , indicate that whilst oxidation with dilute nitric acid splits off from the pinacyanol molecule the quinaldine residue which contains the quinquevalent nitrogen at0.m (forming quinaldinic acid ethyl nitrate) potassium permanganate splits off as ethylquinolone that containing the tervalent nitrogen atom. It thus appears that. the second quinaldine residue is present in pinacyanol in the form (4) It has thus been shown that (i) the carbocyanine condensa-tion takes place between two molecules of quinaldine alkyl iodide and one of formaldehyde and that (ii) the two quinaldine residues are both attached t c ~ the rest of the molecule through the carbo MILLS AND HAMER !THE CYANINE DYES.PART III. 1555 atoms of their 2-methyl groups. the condensation must therefore be The main reaction concerned in PI. 1 This is analogous to several well-known reactions in which one molecule of formaldehyde condenses with two molecules of a com-pound containing EL group of similar reactivity to the %methyl group in quinaldine ethiodide (compare Kiioevenagel Ber. 1894, 27 2345). In the alkaline reaction mixture the hypothetical intermediate product VI would lose hydrogen iodide forming the substance (VII. 1 (VIII.) VII for the existence of reactions of this type is well established (compare Decker Ber.1905 38 2493). VII is however not a possible formula for a substance as intensely coloured as pinacyanol. From analogy to other basic dyes the saturated and the unsaturated nitrogen atoms in this compound must be connected by a chain of conjugated unsaturated1 linkings. There are reasons which make the presence of an ethylenic linking between the carbon atoms 9 and 10 exceedingly probable and therefore we assign to pinacyanol the formula VIII. These reasons are first that in the closely related isocyanine con-densation a similar oxidation involving the removal of two hydrogen atoms occurs,* and secondly as has already been pointed out that the great readiness with which pinacyanol can be oxidised * The two hydrogen atoms by which formula VII differs from VIII would be unusually reactive on account of their respective positions relative to unsaturated linkings and would therefore be readily removable.That the carbocyanine condensation involves a process of oxidation would also explain why a larger yield of sensitiser can be obtained from a given quantity of quinaldine ethiodide when the Condensation is carried out in presence of quinoline ethiodide ; the latter probably gives rise to substances which serve to take up this hydrogen 1656 BEILLS AND HAMER THE CYANINE DYES. PART III. tol quinaldinio acid ethyl nitrate is scarcdy to be accounted for unlem an ethylenic linking is present in this position. There is a somewhat remarkable reaction of pinacyanol which is probably dependent on the presence of this unsaturated three-carbon chain uniting the t’wo quinoline residues.If a solution of the nitrate of the dye in dilute nitric acid is carefully warmed to 60° the orangered colour to which reference has already been made suddenly appears and on cooling t,he solution a bright red compound crystallises. This is a quaternary nitrate and analysis indicates that it is formed by the entrance eibher by substitution or addition of two nitro-groups into t’he pinacyanol molecule. Since on oxidation it gives like pinacyanol itself quinaldinic acid ethyl nitrate and 1 -ethyl-2-quinolone both nitro-groups must be attached to the 3-carboln chain connecting the two quinoline residues unless as is less pro’bable one of them is in the 2’-position. This reaction which does not take place in the presence of carb-amide accordingly recalls the action of nitrogen peroxide on quinoline-yellow (Eibner and Lange Arznaken 1901 315 342), and the stability olf this pinacyanol derivative in comparison with Eibner and Lange’s additive compound would indicate that it is a substitution derivative.(5) According to this view of the constitution of the carbo-cyanines they stand in an interesting relationship to the cyanines. The cyanihes can be regarded as consisting of a l-alkylquinolenyl radicle united through the methenyl group :CEO to a univalent residue of an alkylquinoliniurn salt. Since the union can take place from a 2- to ai 2’-positioln a 4- to a 4’-position or from a 2- to a 4/-position there are three types of cyanines : (111.) The dyes of type I1 are the true cyanines those of type I11 are Dyes of type I are at present unknown in t h e the isacyanines MILLS AND HAMER THE CYANINE DYES.PART JII. 1557 quinoline seriw but the cornpounds obtained by Hofmann (Ber., 1887 20 2262) by the action of ammonia on a mixture of the alkyl iodides of benzothiazole and 1 -methylbenzothiazole are so closely analogomus to the isocyanines in the method by which they are formed and in their properties that Lhey undoubtedly possess the constitution C B < ~ ~ > C :CH* C<$>C,H , /\ R I and thus are repraentatives of this class. According to the constitution now assigned to the carbocyanines, they are cyanines of class I in which the carbon chain connecting the two quinoline nuclei has been lengthened by the introduction of the group =CH:CH*.The great resemblance between the carbo-cyanine and the cyanine dyes thus finds a simple explanation and the dseper collour of the carbocyanines compared with the reddish-purple of the cyanines of the benzothiazole series is associated with the lengthening of the chain of conjugated unsaturated linkings which connects the two nitrogen atoms. Corresponding with the three types of cyanines the following three classes of carbocyanines should be capable of existence: (II’.) /-\ (111’. ) Thus in addition to the dyes of the type of pinacyanol (I/) it should be possible to prepare compounds of the formulae 11’ and III’ which would probably prove to be dyes possessing polwerful photo-sensitising properties similar to those shown by the rest of this group of compounds.EXPERIMENTAL. Composition of I 1’-Diethylcarbocyanine Salts. 1 I’-Dieth2glcarbocyanine iodide prepared as described by Pope and Mills (Eoc. it.)^ by the action of formaldehyde and alkali o 1558 MILLS ANDZHAMER THE CYANINE DYES. PART III. a mixture of quinaldine ethiodide and quinoline ethiodide after having been crystallised five times from methyl alcohol and dried to constant weight a t 145°/20-30 mm. was found on analysis by tjhe Carius method to coatain I=26*60 per cent. The iodide pre-pared from quinaldine ethiodide alone was found in two1 analyses to contain I=26*61 and 26.68 per cent. The iodide pre-pared from quinaldine ethiodide and quinoline methiodide gave I=26.53 and 26.54 per cent.The mean of these values which are probably slightly too high on account of occlusion of silver nitrate by the silver iodide is 26*59* (C,H,N,I requires 1=26.43; Fischer’s formula C,H,N,I requires I = 27.23 per cent.). 1 1’-Diethylcarbocyanine bromide after drying to constant weight a t 140°/20-30 mm. was found to contain Br=18.49 and 18-53 per cent. in two experiments carried out by Mr. J. E. G . Harris. These analyses to which on account of the accuracy of the Carius method for the estimation of bromine we attach especial importance give it molecular weight of 432 for the bromide (corre-sponding with a molecular weight of 479 for the iodide) (C,H,N,Br requires Br = 18.45 ; Fischer’s formula C24HBN2Br requires Br= 19.06 per cent.). Combustion of the dried bromide gave results in excellent agree-ment with the formula C,H2,N,Br (Found C,= 69-18 ; H = 5.83 ; N=6.55.Calc. C=69*26; H=5*82; N=6.47 per cent.). Oxidation of 1 1 1-Diethylcarbocyanine Bromide with Nitric Acid. 1 1’-Diethylcarbocyanine bromide (2 grams) was boiled under reflux with il. mixture of nitric acid (D 1-42; 40 c.c.) and water (40 c.c.). Nitrous fumes were evolved and the liquid rapidly became orangered but the colour gradually disappeared and, after about one hour’s boiling the liquid became co1ourless.t The liquid was then evaporated first on the water-bath and finally over sulphuric acid’ under 2 mm. pressure. The residue was treated with water and a sinall quantity (about 0.1 gram) of undissolved material was removed by extraction with chloroform.The aqueous layer was again evaporated on the water-bath and finally in a highly exhausted desiccator over sulphuric acid. The residue gradually solidified and by trituration with a little acetone an almost colourless crystalline solid was readily isolated. After * These analyses were carried out by one of us and Mr. F. H. Jeffery. t During this operation a small quantity of a heavy volatile oil with a pungent odour resembling that of chloropicrin appeared in the condenser. The amounts obtained were insufficient to enable the substance to be identified but it contained nitrogen and bromine and waa possibly bromo-nitromethane MILLS AND HAMER THE CYANINE DYES. PART III. 1559 recrystallisation from absolute alcohol it melted and decomposed a t logo.The following observations show that this compound is quin-aldinic acid ethyl nitrate : (i) It is a nitrate. An estimation of the NO radicle by ‘ I nitron ” gave NO,=23.6. C,,H,,O,N*NO requires NO,= 23.5 per cent. (Found N = 10.8. C,,H,,0,N2 requires N = 10.6 per cent .). (ii) Although a quaternary ethyl nitrate (as shown by its con-version into ethylquinolone on oxidation and its behaviour with excess of alkali) it was strongly acid and could be sharply titrated with alkali and phenolphthalein and therefore contained a carboxyl group (Found C0,H = 17.05. C,,H,,O,N,*CO,H requires CO,H = 17.04 per cent.). (iii) Its conversion by alkaline f erricyanide into ethyl-2-quinol-one shows that the carboxyl group was in the 2-position. An aqueous solution of the nitrate (0.5 gram) was slowly dropped into a solution of potassium ferricyanide (6 grams) in 5 per cent.sodium hydroxide (60 c.c.) maintained at 0-5O. The resulting liquid was extracted with ether and the residue left on evaporation of the ether after drying with potassium hydroxide was pure 1 -ethyl-2-quinolone. I t s melting point 53-55*5O was identical with that of a specimen of ethylquinolone prepared for comparison by oxidising quinoline ethiodide and a mixture of the two specimens melted a t the same temperature. The weight of quinolone obtained was 0.27 gram or 82 per cent. of the theoretical amount. The material from which the quinaldinic acid ethyl nitrate had been separated by means of acetone was then examined. It was left after evaporation of the acetone as a clean brown oil which was excessively soluble in water alcohol or acetone.It was investigated in various ways such as by crystallisation of the platinichloride without much further information being gained. It was therefore oxidised with alkaline potassium f erricyanide. The material obtained from 2 grams of diethylcarbcwyanine bromide by oxidation with dilute nitric acid and subsequent removal of the quinaldinic acid ethyl nitrate was dissolved in water a small quantity of insoluble matter being removed by filtration and the liquid was dropped into a solution of potassium ferricyanide (8 grams) in 5 per cent. sodium hydroxide solution a t 0-5O. The quinolone produced was extracted with ether and dried with potassium hydroxide.The material from three such experiments was united and dis-tilled under 2 mm. pressure from an oil-bath a t 155-168O. The distillate was a colourless oil which solidified to crystals meltin 1660 MILLS AND HAMER THE CYANINE DYES. PART III. a t 50-54O with previous softening a t 40°. It was therefore not quite pure and was recrystallised from light petroleum. It then melted a t 50-54-5O and was shown by its general characters and analysis to be 1-ethyl-2-quinolone (Found N = 8.3 Calc. N = 8'1 per cent.). The quantities obtained in these experiments were as follows. By the oxidation of 6 grams of 1 l'-diethylcarbocyanine bromide, C,,H~N,Br,CH,OH 3.03 grams of quinaldinic acid ethyl nitrate were obtained. This melted at 107-108° and' was pure (Found: C02H = 17.2 ; NO,= 23.6.Calc. C02H = 17-04 ; NO,= 23.5 per cent.). This weightl is 89 per cent. of that theoretically obtainable. The weight of crude 1 -ethyl-2-quinolone obtained was 1.64 grams. The weight of redistilled material was 1-35 grams which is 60 per cent. of the weight of quinolone theoretically obtainable from one quinaldine nucleus in the pinacyanol taken. The weight of recrystallised material from which the sample for analysis was taken was 0.76 gram. Oxidation of 1 l 1-Diet~tylcarbocyanine Acetate with Potassium Permunganate. To prepare the acetate a solution of 1 1 1-diethylcarbocyanine bromide (4 grams) in boiling rectified spirit (450 c.c.) was treated with it hot saturated aqueous so'lution of silver acetate (1.44 grams). The residue olbtained after evaporating the filtrate from the pre-cipitated silver bromide was dissolved in a mixture of acetone (450 c.c.) and water (450 c.c.).Into this sollution which was mechanically stirred and kept a t 0-5O 140 C.C. of a solution of potassium permanganate containing 3.16 grams per litre were slowly dropped an snd-pointl having been reached when 137 C.C. had been added. The red filtrate which was neutral to litmus, was extracted with ether after evaporating the acetone under diminished pressure. The broiwn ethereal extract .was shaken with very dilute hydrochloric acid which extracted some tarry matter (0-18 gram) leaving an almost colourless solution. This was dried with potassium hydroxide and1 then evaposated ; the residue (1.26 grams) which soon crystallised melt'ed a t 45-50°.When distilled under diminished prelssure this gave a colourless distillate of pure 1 -ethyl-2-quinolone (melting point 52-55O ; melting point of a mixture with pure 1 -ethyl-2-quinolone 52-55') (Found C=76*1; H=6*7. Calc. C=76*3; H=6*4 per cent.). The weight of the dist'illate was 1.18 grams which is 79 per cent. oQ the theoretical yield. The aqueous solution left after extraction of the ethylquinolon was acidified with hydrochloric acid evaporated and the residue then treated with absolute alcohol to separate the organic matter from potassium chloride. The brown material left after evaporation of the alcohol was boiled for thirty hours with 140 C.C. of dilute nitric acid (D 1*2), and the solution was then examined in the same way as that obtained by oxidising diethylcarbocyanine bromide with nitric acid.The weight of quinaldinic acid ethyl nitrate obtained was 0.61 gram or 27 per cent. of the theoretical amount and further oxidation of the residual material with alkaline f erricyanide gave 0.46 gram of ethylquinolone equivalent to 31 per cent. of the theoretical yield from the original diethylcarbocyanine acetate. The Red Salts obtained by the Action of Nitric Acid on 1 1 f-Diethylcarbocyanine Salts. 1 1'-Diethylcarbocyanine brolmide (1 gram) was dissolved in dilute nitric acid by warming to 40° with a mixture of 4 C.C. of nitric acid (D 1*42) previously boiled to expel oxides of nitrogen, and water (16 c.c.). The bromine was then exactly precipitated with silver nitrate and the blue or green filtrate containing the nitrate of the dye was warmed to 60-65O when the liquid suddenly turned orange and red crystals began to separate.The liquid was cooled to Oo and the crystals were collected. By boil-ing the filtrate a short time and coaling to Oo a further yield was obtained and the process of boiling the filtrate and cooling was repeated as long as fresh quantities of crystals separated; 13 grams of 1 1'-diethylcarbocyanine bromide thus treated gave 7.36 grams of the red crystals. The yield is less if larger quantities of carboc eyanine than 1 gram are taken. The reaction is dependent on the production of oxides of nitrogen. If commercial nitric acid not previously boiled is employed the colour change takes place considerably below 60°.On the other hand if carhamide is added the mixture can be boiled without the formation of the red salt. This red salt is a quaternary nitrate. To obtain EL compound which could be more accurately analysed it was converted' into the correspolnding bromide by dissolving in boiling water and adding the solution to an equal volume of a hot concentrated solution of potassium bromide. The red bromide began to) crystallise from the hot solu-tion and separated practically completely on cooling. This treat-ment with potassium bromide was then repeated three times and the product was finally recrystallised from hot water 1562 MILLS AND HAMER THE CYANINE DYES. PtLRT III. For analysis it was dried a t 50°/20-30 mm. The dried material melted and decomposed a t 201-202O (Found C =56.76, 56.65 ; H =4.80 4-58 ; N = 10.52 10.73 ; Br = 15.37 15.37 15.16.CZ5Hz3O4N4Br requires C = 57.4 ; H = 4.42 ; N = 10.7 ; Br = 15.27 per cent. Loss on drying 6-92 7.75. C25H,304N,Br,2H,0 requires H20 = 6.9 per cent.), Oxidation of the Red Nitrate.-One gram was boiled with a mixture of 10 C.C. of nitric acid (D 1-42) and water (10 c.c.). Oxides of nitrogen were evolved the colour slowly faded and, after boiling under reflux for six hours a pale yellow liquid was obtained. This liquid was treated in the same way as the similar solution obtained by oxidising diethylcarbocyanine bromide with dilute nitric acid (p. 155S) and the same products namely, quinaldinic acid ethyl nitrate and l-ethyl-2-quinolone were similarly isolated. From 4 grams of the red nitrate correspond-ing with 3-95 grams of anhydrous substance were obtained 1.51 grams of quinaldinic acid ethyl nitrate (73 per cent. of the theoretical quantity) and 0.84 gram of ethylquinolone melting a t 52-53" (62 per cent. of the theoretical quantity). Colrresponding experiments were carried out with the bromide. This salt was much more rapidly attacked by the dilute nitric acid, the bromine present evidently assisting the oxidation and the volatile heavy oil to which reference has already been made (p. 1558) appeared in the condenser otherwise the products of oxidation were the same. Quinaldinic acid ethyl nitrate and 1-ethyl-2-quinolone were obtained in quantities corresponding with 93 per cent. and 60 per cent. respectively of the theoretical amounts. One of us (F.M.H.) is indebted to the Department of Scientific and Industrial Research for a grant for which she desires to express her thanks. UNIVERSITY CHEMICAL LABORATORY, CAMBRIDGE. [Received October %Oth 1920.