460 XXXVI1.-Researches on the Constitution of Azo- and Diazo-derivatives. I I I . Compounds of the Naphthalene @-Series. By RAPHAEL MELDOLA F.R.S. and F. J. EAST Introductory. WHEN diazo-salts are allowed to act on naphthalene-derivatives of the p-series such as &naphthol or 6-naphthylamine azo-compounds are readily formed the pu’,-group generally entering the a- (ortho) posi-tion with respect to the P-substituent. That the displaced hydrogen-atom has a t least in the majority of compounds hitherto investigated, the above-mentioned position is now placed beyond doubt by the work of numerous chemists and there is no occasion to restate the evidence for what is now a generally received view. The azo-compounds of the naphthalene @series which comprise a large pro-portion of the azo-dyes met with in commerce differ however in so many of their properties from the other azo-compounds that it has been lately called in question whet,her tbey belong to the same class of derivatives.Thus the azo-derivatives of a-naphthol show by their phenolic character the undoubted presence of hydroxyl whereas the corresponding p-naphthol-compounds have until recently given no distinct evidence of the presence of the hyciroxyl-group. Similarly with respect to the azo-derivatives of P-naphthylamine it was pointed out by one of the authors four years ago (Trans. 1884 117) that these differed in many ways from the corresponding a-naphthylamine-derivatives a fact which has since received ample corroboration from the researches of Zincke and his pupils.Among the points in which the azo-derivatives of P-naphthylamine differ from the corresponding a-compounds is the difference in the facility with which the two classes of compounds can be diazotised. The P-derivatives in fact appeared a t one time t o have been con-sidered as being incapable of diazotisation and this was especially the case with respect to the compounds obtained by the action of the diazotised nitranilines on P-naphthylamine investigated by one of the authors (see the paper referred to Trans. 1884 116). For the reason just stated i l was supposed that the derivatives in question did not contain an amido-group and a formula was therefore sug-gested for these compounds i n accordance with which they were represented as related to the azimido-compounds of Griess.An analogous view with respect to the azo-6-naphthol-compounds was about the same time put forward by Lieberrnann (Ber. 1883 2858) THE COXSTITUTION OF AZO- AND DIAZO-DERIVATIVES. 4Gl who concluded from the circumstance that benzeneazo-@-naphthol is insoluble in aqueous alkali that these oxyvazo-@-derivatives did not contain hydroxyl. The two formulae thus proposed as alternative to the generally received views were the following :-(4 (4 (PI (B) clOH6<f;:>N*x Cl0H6 < ;g>N*x. Zincke who had previously been investigating the action of phenyl-hydrazine on the naphthaquinones shortly afterwards put forward the view that the oxyazo-@-compounds were constructed on the type of hydrazides (Ber. 1885 3135 ; 1886 1461 ; and 1887 1169).This view of the constitution of the compounds in question appears to be maintained by Zincke (Bey. 1887 2903) and in accordance therewith the formule would be written-0 NH CIOH6/ 1 ClOH8 I \N-NH.X \N.NH.X' The conclusion arrived a t by one of the authors with respect to the absence of the amido-group in the p-naphthylamine azo-compounds was as already stated based upon negative evidence that is the non- diazotisable character of para- and meta-nitrobenzeneazo-p-nnphthylamine. In 1886 however the generality of this conclusion was shaken by the discovery by Niefzki and Go11 (Ber. 1886 1281) that amidoazo-P-naphthalene could be converted into oxyazo-F-naphthalene by means of the diazo-reaction. This fact although strongly suggestive of the presence of NH in the compound in ques-tion could not be taken as it complete proof Rince the reaction may also be interpreted in accordance with the formula proposed by one of the authors o r with that of Zincke.It is in fact not inconceivable that the NH-group and nitrous acid may interact according to either of the equations :-NH 0 ClOH6' I + O:N*OH = C10H/I + Nz -I- HZO. 'N*NH-X \N-NH.X The diazo-salt$s of benzeneazo-P-naphthylamine have however been since isolated by Zincke and Lawson (Bey. 1887 Z896) and it is diE-cult to see how this result can be interpreted in any other way tllan by admitting the presence of an amido-group in the original compound 462 MELDOLA AND EAST THE CONSTITUTION OF It was suggested by one of the authors in 1884 (Chern. News, December 5th) that much light would be thrown on the constitution of these and other azo-compounds by investigating the products of reduction of their acetyl- or alkyl-derivatives.This method has already been extensively applied to the investigation of the constitu-tion of the diazoamido-compounds in the series of papers communi-cated to the Chemical Society by one of the authors in conjunction with Mr. F. W. Streatfeild (Trans. 1886 625 ; 1887 102 and 434 ; B e y . 1886 3239). The investigation of the diazoarnido-alkyl-derivatives is still in progress and much work has yet to be done in this direction as the first result of the application of the method has been the discovery of a new and quite unexpected class of cases of isomerism about which me shall have more to say shortly.I n the meantime the formation of an acetyl-derivative of azirnidotoluene by the action of nitrous acid on acetyl-orthotoluylenedinmine observed by Roessneck (Ber. 1886 1757) shows that the constitution of the azimido-compounds as pointed out by one of the authors (Phil. Ma,g. June 1857 525) is more probably that assigned by Kekul6 and Ladenburg :-This conclusion has been recently confirmed by Niilting and Abt, (Ber. 1887 2999) by the method of alkylation so that another formula, for the azo-derivatives of the naphthalene-&series thus becomes; possible :-With respect to the oxyazo-P-naphthalene-compounds it has been recently shown by Weinberg (Be?-. 1887 31 71) that benzeneazo-/3-napht,hol forms an ethyl-derivative which on reduction furnisheti diamidoethoxpap hthylphenyl -NH,*CJL*CioH,O[ CJ35(P)].NJ&(a).Weinberg justly concludes from this circumstance that the ,B-oxy-azo-compounds contain hydroxyl. While the present research was in progress a paper has appeared in which P. Jacobson (Ber. 1888, 414) gives additional evidence in favour of the older view of the con-stitution of benzeneazo-@naphthol. This summing up of the present position with reference to the con-stitution of the naphthalene-p-azo-compounds will render it evident that the question as to the presence of hydroxyl and amidogen in these derivatives has been practically reopened Sy the expwimental results recentJy obtained. These results must certainIy be regarded as oppose AZO- AKD DIAZO-DERIVATIVES. 463 to the azimido-formula as well as t o the hydrazide-formula of Zinckc.Two years ago further experiments in the direction indicated in 1884 (the method of acetylation and alkylation) were commenced by one of the authors and Mr. F. W. Streatfeild but the work was temporarily interrupted in order to carry on other investigations. The chief con-clusion arrived at in these first experiments was that the compounds obtained by nitriting the nitroazo-derivatives of p-naphthylamine in acetic acid were not as had been at first aupposed nitroso-derivatives, although the products thus formed had neither the characters of the original compounds nor the corresponding oxyazo-compounds nor of diazo-compounds so that it was evident that some distinct reaction had occurred. In order to gain further insight into the course of t8his reaction the research has been recently resumed and at the same time other P-naphthaleneazo-compounds which appeared likely to throw light on the question of the constitution of these derivatives have been comprised in the investigation the results of which we now submit t o the Society.The Action of Nitrous Acid in the Presewe of Acetic Acid on the Azo-conzpounds obtained by the Action of Diaxotised Para- and Meta-nitraniline on 6-naphthylarnine. The first experiments mere made with metanitrobenzeneazo-p-naph-thylamine m. p. 182" (Trans. 1884 116).* The action of nitrous acid on this compound dissolred in glacial acetic acid varies according t o the conditions of the experiment. If the substance is dissolved in a sufficient quantity of acetic acid to keep it in solution in the cold a diazo-compound is first formed when the necessary quan-tity of sodium nitrite is added to the solution.On boiling nitrogen is evolved and on distilling off the acid or on diluting with water, metanitrobenzeneazo-/3-naphthol (Trans. 1885 668) separates out. This compound was identified by its melting point (194") and by the following analyses :-I. 0.1058 gram gave 0.2558 gram CO and 0.0374 gram H,O. 11. 0.2204 , 0.5284 , 77 09753 79 9, 111. 0.2298 ,, IV. 0.0998 , 12 , , 13.3" C. , 749 ,, 27.4c.c. N at 15.5" C. and 759.7 mm. bar. Calculated for Found. - - C . . 65-52 65.93 65.38 H 3-73 3-92 3-79 N 14.33 - 13.92 13-96 - -* In the paper above referred to the melting point is erroneously given as 177' 464 MELDOLA AND EAST THE CONSTITUTION OF In effecting this reaction,it is necessary to use a very large quantity of acetic acid owing to the sparing solubility of the azo-compound in this solvent one part of the nitrobenzeneazo-p-naphthylamine requiring about 140-150 parts of glacial acid to keep it in solution in the cold.The same reaction takes place at once if one-third of this quantity of acid is used and the nitrite is added to the solution raised to just its boiling point. The results obtained on working by either of these methods show that the reaction is in this case quite normal and analogous to the conversion of benzeneazo-/?-napht h y lamine into benzeneazo- {J-naph tho1 (Zincke Ber. 1887 2898). The chief point of interest in connec-tion with the present method of carrying out the reaction is that it takes place in the absence of any strong mineral acid.By repre-senting the free diazo-conipound as the first product the reaction may be regarded as the following :-We may add that the diazo-salts of metanitrobenzeneazo-p-naph-thylamine are extremely unstable and no attempts have as yet been made to isolate them. If instead of working in the manner just described a much smaller quantity of acetic acid is used and the temperature is kept below 70" during the whole operation the reaction takes an entirely different course. Cnder these circumstances nitrogen is given off as before, and a substance crjstallising in beautiful orange-brown scales gradually separates. After purification by crystallisation from acetic acid and then from alcohol this compound was obtained in the form of red filamentous needles melting at 161-162" and giving the following results on analysis :-J.0.1512 gram gave 0.3598 gram COz and 0.0535 gram H,O. 11. 0.1445 , G.3416 , , 0.0530 , ,, 111. 0-1883 ,, The formula deduced from these numbers showed that the sub-staolce was the ncetyl-derivative of metanitrobenzeneazo-&naphthol :-19.1) C.C. N at 11.5" C. and 779.1 mm. bar. Calculated for Found. 7 N2*C,jH,*NO9 (.-.-C10H6<C).C,H,0 ' I. 11. 111. c 64.44 64.89 64-47 -H 3-93 4.07 - 3.85 N 12.53 - - 12.82 The following are the details of the method of performing the re AZO- AKD DIAZO-DERIVATIVES. 465 action :-One part of the nitroazoamido-compound is heated with about 70 parts of glacial acetic acid till completely dissolved and the solution then allowed to cool down to 60-70".The theoretical quantity of sodium nitrite is then added in the solid state in small quantities at a time the Oemperature of the solution not being allowed to rise above 70". The contents of the flask are well shaken after each addition of nitrite and each quantity of the latter is allowed to dissolve before adding more. When all the nitrite has been added the solution is set aside to cool and the crystalline acetyl-derivative can be collected after 6-8 hours. From the foregoing result it will be seen that when metanitro-benzeneazo-/I-naphthylamine is treated with sodium nitrite in the presence of acetic acid under the conditions specified the acetic acid takes part in the reaction :-It is of course possible that an unstable diazo-compound is formed as an intermediate product this compound immediately undergoing decomposition in presence of the acetic acid according to the follow-ing scheme :-/N,.C6H,.NO cIoH,\;N ; ,.;OH! :.-" " ' i H.10 .C,H,O 1.. That the acetyl-derivative has the constitution assigned to it was shown by cohobating the compound with one molecular proportion of potassium hydroxide dissolved in alcohol when the acetyl-group was easily removed and metanitrobenzeneazo-p-naphthol (m. p. 194') was obtained. The yield of acetyl compound is practically quantitative, and as the reaction promises to be widely applicable for the synthesis of phenolic acetates and other ethereal salts it is proposed to extend the investigation in this direction and to make a special study of the conditions which determine the displacement of amidogen by the C,H,O*O-group by means of the diazo-reaction.It will be of interest here to point out the analogy of this reaction to that in which phenolic alkyl-ethers are formed by the action of diazo-salts on alcohol :-(Fittica Ber. 1878 1209; G. Schultz Ber. 1884 and 475; Haller, Ber. 1884 1887 ; Hofmann Ber. 1884 1917 ; Wroblewsky Ber. 466 JIELDOLA AND EAST THE COSSTITUTIOS OF 1884 2703; Remsen Bey. 1885 65; and Amer. Chern. J. 8 243 and 9 387). Paranitro benzeneazo-P-naphthylamine (Trans. 1883,430) undergoes a similar decomposition when treated with sodium nitrite in the presence of acetic acid.One part of the nitroazo-compound was dissolved in 140-150 parts of the glacial acid and the necessary quanity of sodium nitrite added to the solution the temperature of the latter not being allowed to rise above 70". Paranitrobenzeneazo-/3-naphthgl acetate crystallises out on cooling in beautiful red flat-tened needles having a slight violet reflexion. The melting point is 192-193". After crystallisation from alcohol in which the sub-stance is soluble only with great difficulty it was obtained in the form of flat orange needles having the same melting point. The following analyses were made by Mr. Streatfeild :-I. 0.1484 gram gave 0.3510 gram CO and 0.0523 gram H,O. 11. 0.1988 , , 0.4694 , , 0.0724 9 9 I Calculated for Found. N2.OcH.j *NO2 '1oH6<() .C,H,O * I.11. c 64.44 64.50 64-39 H . 3.85 3-91 4-04 The acetyl-derivative like its metanitro-isomeride is readily de-composed by boiling for a short time with one molecular proportion of potassium hydroxide dissolved in alcohol the acetyl being removed and paranitrobenzeneazo-@naphthol rn. p. 249" (Trans. 1885 662), being formed. Acetylation of Oxyazo-P-Naphthalene Compounds. I n order to ascertain whether acetyl-derivatives could be obtained by direct acetylation as well as by the diazo-reaction with acetic acid, metanitrobenzeneazo-6-naphthol (m. p. 194') was boiled for about 12 hours with acetic anhydride and anhydrous sodium acetate. The product after being washed with water and crystallised from alcohol, proved to be identical with the acetyl-derivative of m.p. 161-162" obtained in the manner described in the foregoing part of this paper. The acetylation of the nitroazo-compound could not be effected in less time than that specified. Benzeneazo-P-naphtli y l acetate.-In order to prepare this compound, benzeneazo-P-naphthol was boiled with acetic anhydride and dry sodium acetate for 24 hours the acetylation not being completed in less time. The product after being washed with water and crystal-lised two or three times from alcohol was obtained in the form o AZO- Ah'D DIAZO-DERIVATIVES. 467 deep orange-coloured scales melting at 117". numbers on combustion :-It gave the following 0.1520 gram gave 0.4130 gram CO and 0.0679 gram H,O. 0.2463 , , 20 C.C. N at 14.5" and 772.4 mm. bar. Calculated for NO'C6H5 '10I16 < 0:C2H30' Found.C . 74-48 74.1 6 H . 4-82 4.93 N . 9.65 9-68 It follows from these results that the azo-derivatkes of p-naphthol contain one atom of hydrogen capable of being displaced by acetyl, and the experiments of Weinberg already referred to have show-n that these compounds are also capable of being ethylated. I n order to clear up the constitution of these derivatives i t is only necessary to ascertain whether the acetyl- or alkyl-group is attached to oxygen or nitrogen that is to find out whether the displaced hydrogen-atom is imidic or hydroxylic. That the latter is the case is shown by the conversion of metanitrobenzeneazo-p-naphthylamine into metanitro-benzeneazo-/I-naphthyl acetate by means of the diazo-reaction with acetic acid as described in the present paper.This acetate is identical with that produced by the direct acetylation of netanitro-benzeneazo-&naphthol and is converted into the latter by hydrolysis. We have not yet succeeded in converting benzeneazo-P-naphthyl-amine into benzeneazo-/3-naphthyl acetate by the diazo-reaction with acetic acid,* but since Zincke has shown that this reaction in the presence of water converts the amido-6-azo-compound into the corre-sponding benzeneazo-@naphthol the chain of evidence is so far com-plete. The direct proof of the Constitution of these P-azo-derivatives of naphthalene will however be only forthcoming when the products of complete reduction have been studied. We have already made a large number of experiments in this direction but have met with so many practical difficulties that we prefer to withhold the results for the present. We may state in conclusion that the whole of the evidence thus far obtained points distinctly to the existence of hydroxyl and amidogen respectively in the p-oxyazo- and /I-amidoazo-compour,ds of naphthalene but we refrain from offering any opinion upon the constitution of these derivatives until more experimental evidence has been obtained. Finsbury Technical College, .March loth 1888. * Acetic anhydride cannot be used in this reaction as it acts so energetically on benzeneazo-,8-naphthylamine that complete decomposition with the formation of resinoue products takes place