COLOUR AND CONSTITUTlON OF DIAZONIUM SALTS. PART 111. 2557CCLXL- The Colour und Constitution o f DiazoniumSalts. P a ~ t III. The Diazo-derivatives of 2 7-Naphth ylenediamine.By GILBERT T. MORGAN and FRANCES M. G. MICKLETRWAIT.ALTHOUGH the diazo-derivatives of the diamines of the benzene anddiphenyl series have been extensively studied, owing largely to thecircumstance that in many instances these products are of consider-able industrial importance, yet comparatively little attention hasbeen directed to the diazonium salts of the naphthylenediamines.Of the ten naphthylenediamines, three, namely, the 1 : 2-, 2 : 3-,and 1: 8-compounds, are known to yield cyclic diazoimines (DeAguiar, Ber., 1874, 7, 316; FriedlLnder and von Zakrzewski, Ber.,1894, 27, 764; Morgan and Godden, this vol., p.1707); the remain-ing seven give diazonium salts of varying degrees of stability (Ewerand Pick, D.R.-P. 45549, 45788 ; Badische Anilin- & Sod%Fabrik,The case of 2 : 7-naphthylenediamine has recently been examiuedby Kaufler in connexion with his theory of the stereochemicalconfiguration of naphthalene and other polynuclear hydrocarbons.According to Kaufler, the two nuclei present in naphthalene arebent round, using their two common carbon atoms as axis, so thatthe lateral extremities of the molecule represented by the positions2 : 3 and 6 : 7 become contiguous. This supposed folding of thetwo nuclei would bring the two amino-groups of 2 : 7-naphthylene-diamine into close proximity, and Kaufler claims that the intimateassociation of these two groups is manifested by certain phenomenaof steric hindrance which are advanced in support of hishypothesis * (Annaben, 1907, 351, 154; Ber., 1907, 40, 3251).It is asserted that the amino-groups of 2 : 7-naphthylenediamineexert a mutual inhibiting influence on each other, with the resultthat only one amino-group is diazotisable.I n diazotising the hydro-bromide or the hydrochloride of the diamine, Eaufler and Karrerworked in acetic acid or alcoholic solution, and fobnd that evenD.R.-P. 130475).* It may be pointed out that Kaufler’s view is a t variance with the ideasembodied in the KekulB-Baeyer conceptioii of the naphthalene molecule based on t,hetetrahedral carbon atom and t h e strain hypothesis, and also with the naphthalenemodel advocated by Pope and 13arlow on crystallographic grounds.These con-ceptions, which may be termed respectively the functional and structural repre-sentations of naphthalene, although differing in many respects, concur in placingthe 2 : 3- and 6 : 7-positions, not in contiguity, but a t the lateral extremities of themolecule2558 MORGAN AND MICKLETHWAIT: THE COLOUR ANDwith excess of amyl nitrite only the monodiazonium salt was pre-cipitated (Ber., 1907, 40, 3263).This result is dependent, however, not on steric hindrance, buton experimental conditions. By operating with sodium nitrite ornitrosyl sulphate in moderately concentrated sulphuric acid, theauthors have succeeded in diazotising completely both the amino-groups of the diamine.Probably the diazotisation occurs in twostages, and the isolation of the intermediate amino-diazonium saltsby Kaufler and Karrer is dependent on the insolubility of thesesubstances in the media employed.EXPERIMENTAL.Naphthalene-2 : 7-&isdiazo?zium Sdphate ( I ) ,H SO4*N,*C1,H,-N2* HSO,,&H,OH.Recrystallised 2 : 7-naphthylenediamine (0.5 gram), melting at160-161°, was dissolved in 2 C.C. of cold concentrated sulphuricacid, mixed with 1 gram of ice, and diazotised with 2 grams ofnitrosyl sulphate, the mixture being cooled by further addition of1 gram of ice. The cold filtered solution was carefully added to amixture of two parts of ether and one of alcohol, and if the pre-cipitated sulphate was viscid, more alcohol was added. The lightyellow crystals thus obtained were washed with a mixture of etherand alcohol, and finally with ether; the yield of diazonium sulphatewas 86 per cent.of the calculated quantity. The salt was appreciablysoluble in alcohol, and when precipitated by ether in the presenceof alcohol it retained a definite amount of the latter solvent, evenafter prolonged drying in the vacuum desiccator. The followinganalyses were carried out on different preparations which had beendried for varying periods :0-2116 gave 0.2562 CO, and 0.0562 H,O. C= 33.02 ; H =2.95.0.1385 ,, 0.1688 CO, ,, 0'0334 H,O. C=33.24; H=2.68.0.2020 ), 0'2446 CO, ), 0'0514 H,O. C=33*02; H=2*82.0-07810.2178 ,, 0'2570 BaSO,. S= 16-20.0.1930 ,, 0.2356 BaSO,.S = 16.76.CloHsO8N4S,,&H,O requires C = 33.08 ; H = 2-75 ; N = 14-03 ;S = 16.04 per cent.The bisdiazonium sulphate readily dissolved in water to a clearyellow solution, which was employed in the production of thefollowing diazonium salts.,, 10.0 C.C. N, at 22O and 756 mm. N=14.56.Naphthalene-2 : 7-bis&azonium plathichloride,C,,H,",I,PtC'1,, 2 H,O,separated as a brownish-yellow, crystalline precipitate on addinCONSTITUTION OF DIAZONIUM SALTS. PART III. 2559aqueous chloroplatinic acid to the solution of the bisdiazoniumsulphate. The air-dried salt was not explosive, and could be warmedwithout decomposition :0-1378 gave 0.0964 CO, and 0,0244 H,O. C = 19.08 ; H = 1.96.0'1760 ,, 0.1243 CO, ,, 0-0269 H,O. C=19*26; H=1'70.0.21700.1542 ,, 0'2122 AgC1.Cl=34.02.0.1872 ,, 0.0594 Pt. Pt=31a73.0.1888 lost 0.0114 H20 a t 70-80O.,, 18.0 C.C. Nz at 22O and 756 mm. N=9.42.H20=6*04.C,,H6N4C16Pt,2H20 requires c= 19.16 ; H = 1-59 ; N = 8-94 ;C1= 34.02 ; Pt = 31.15 ; H,O =5-75 per cent.lvaph thalene-2 : 7- b isdkzonium auricht?ode, C1,H6(N2*AuC~,),,was obtained as a reddish-brown, crystalline precipitate on mixingaqueous solutions of chloroauric acid and the bisdiazonium sulphate.The aurichloride was very soluble in alcohol, and even dissolvedslightly in ether :0.1799 gave 0.0936 CO, and 0.0172 H,O. C = 14.19 ; H = 1-06.0.3118 N=6.77.0.1290 ,, 7.7 C.C. N, ,, 20'5O ,, 758 mm. N=6.79.0.1620 ,, 0.2170 AgC1. C1=33*15.0.1834 ,, 0.0834 Au. Au=45*47.,, 18.5 C.C.N, at 20'5O and 760 mm.Cl,H6N4C1,Au requires c = 13.95 ; H = 0.69 ; N = 6.51 ; C1= 33-02 ;Au=45*81 per cent.Naphthalene - 2 : 7 - bisdiaaonium dichromate, C1OH6[IN&Cr20,,separated either in reddish-brown leaflets or brown, nodular crystalson adding chromic acid or sodium dichromate to a dilute solutionof the bisdiazonium sulphate :N = 14-07 ; 0.2184 gave 24.4 C.C. N, at N.T.P. and 0.0824 Cr20,.Cr = 25.81.Cl,H60,N,Cr2 requires H = 14.07 ; Cr = 26-13 per cent.The bisdiazonium dichromate is extremely explosive, and detonateswith a bright flash when gently heated or even on rubbing.The bisdiazonium sulphate gave rise to sparingly soluble diazo-derivatives when added to aqueous solutions of alkali vanadates,mol yb dat es, and tungstat es.The Sandmleyer Reaction with the Bisdiazon/ium Salts of2 : 7-Naphthylenediamine.The purified naphthalene2 : 7-bisdiazonium sulphate (carefullyfreed from any excess of nitrous acid) was dissolved in water andadded to it hydrochloric acid solution of cuprous chloride.2 : 7-Di-chloronaphthalene separated immediately, and was purified bysublimation, when it melted a,t 114-115O, and did not depress th2560 MORGAN AND MICKLETHWAIT: THE COLOUR ANDmelting point of a specimen prepared from naphthalene-2: 7-di-sulphonic acid, for which the aut.hors are indebted to ProfessorArmstrong.This Sandmeyer reaction gave the same result when repeated withthe other bisdiazonium salts of 2 : 7-naphthylenediamine.2 : 7-Bistriazonaphthalene (Naphthylerrte-2 : 7-bisazoimide),2 : 7-Biistriasonaphthalene (11) was obtained as a brownish-whiteprecipitate on adding sodium azide to a well-cooled aqueous solutionof the bisdiazonium sulphats which had been carefully freed fromnitrous acid.The product crystallised from petroleum (b. p.60-80O) in almost colourless leaflets or tabular prisms, whichreddened on exposure to light; it melted at 98O :0.1984 gave 0.4158 CO, and 0.0569 H,O.0-0784C,,H6N6 requires c = 57.14 ; H = 2.85 ; N = 40.00 per cent.2 : 7-Bistriazonaphthalene has a characteristic odour, recallingthat of P-ethoxynaphthalene; it can be partly decolorised by boilingwith methyl alcohol and animal charcoal, and crystallises from thissolvent in very pale pink plates. Cold concentrated sulphuric aciddecomposes the bistriazo-compound with effervescence.The decomposition of the bisdiazonium sulphate with sodiumazide is practically quantitative, and as 2 : 7-bistriazonaphthaleneis only very sparingly soluble in water, its amount can be deter-mined :0.1398 CloH6(NzoHS0,)z,SC,H,*OH gave 0-0741 CloH6(N3)2, melt-ing at 98O, whereas the calculated amount is 0.0736.The aqueous filtrate from the precipitated bistriazo-compound,which contained the alcohol of crystallisation of the bisdiazoniumsulphate, gave a distinct iodoform reaction, thus confirming theanalytical data for this salt.C = 57.14; H =3*18.,, 27.0 C.C.N, at 22O and 760 mm. N=39*84.THEORETICAL CONSIDERATIONS.The f a c t that the 2-aminonaphthalene-7-diazonium salts isolatedby Kaufler and Karrer (Zoc.cit.) and the naphthalene-2: 7-bis-diazonium sulphate described above are yellow compounds affordsadditional evidence in favour of the view that diazonium salts ofnormal constitution display colour when their diazo-complexes areassociated with polynuclear hydrocarbon radicles (compare this vol.,p. 1691).The successive diazotisation of 2 : 7-naphthylenediamine salts iCONSTITUTION OF DIAZONIUM SALTS. PART III. 2561two stages is of interest in connexion with the authors' views onthe constitution of diazonium salts.In the first place, it should be noted that all the available evidencestrongly supports the assumption that the diazotisability of a basedepends on the association of its aminqroup with an unsaturatedorganic complex.This complex need not necessarily be aromaticor even cyclic, but it is, apparently, essential that this group shouldbe unsaturated, for hitherto no amine possessing a fully saturatedradicle has ever been diazotised. The existence of a certain degreeof residual affinity is a necessary condition for the production ofdiazonium salts.I n the aromatic series this residual affinity is supplied by thefourth valency of each carbon atom of the six-membered rings, andthe chemical properties which characterise aromatic amines(oxidation, diazotisation, etc.) may be supposed to- arise from theinteraction of these bases in their tautomeric forms (compare Cain,Trans., 1907, 91, 1051).It cannot be too strongly emphasised that diazotisation is aprocess which takes place only with the undissociatecl salt of anamine, and not with the base itself.Accordingly, the nitrous acidreacts with the salts (for example, the hydrochloride) of the basein the following t,automeric forms :Regarded in this way, diazotisation, which consists in the replace-ment of three labile hydrogen atoms by nitrogen, lea.ds naturallyto the formation of three tautomeric forms of the diazoniunichloride 2562 MORGAN AND MICKLETHWAIT: THE COLOUR ANDIn the special case of the salts of 2: 7-naphthylenediamine, theprogressive diazotisation arises probably from the circumstance thatthe two diazonium complexes represent two phases of the diazo-configuration. If the first formed diazonium complex has the para-hemiquinoid structure, then the second will be in the ortho-hemiquinoid phase, and vice versa :H H H HThe foregoing hypothesis of the constitution of diazonium saltsis based on the assumption that the aromatic amines and their saltsare able to react in the tautomeric imino-forms, a change whichis possible only when the orgapic complex associated with the amino-group is unsaturated.Tautomeric change to the imino-form is possible in the followingnon-aromatic amines, all of which have manifested to some extentthe property of diazotisability :The sminotriazoles (Thiele and Manchot, Annalen, 1898, 303,33) :4-Amino-l: 5-diphenyl-l : 2 : 3-triazole (Dimroth, Frisoni, andMarshall, Ber., 1906, 39, 2925) and aminoant,ipyrine (Knorr andStolz, Anmlen, 1896, 293, 67), represented respectively by formukI and 11:Aminophenylpyrithiazinone (Harries and Klamt, Ber., 1900, 33,1158) and aminotetronic anhydride (Wolf€ and Liittringhaus,AnnuZen, 1900, 312, 133), with formulz I11 and IV:>o NPhoN HO g-CHN H; C-CO(111.) (IV.)In addition to these non-aromatic amines, in which the amino-group is associated with a cyclic structure, an interesting extensionof the diazo-reaction has recently been discovered by K.A. Hofmann,H. Hock, and R. Roth (Ber., 1910, 43, 682, 1087), who find thatunder certain conditions aminoguanidine furnishes diazonium saltsCONSTITUTION OF DIAZONIUM SALTS. PART III. 2563derived, however, not from salts of the base itself, but from amore complex molecule containing two guanidine residues andhaving a greater degree of unsaturation.The diazonium nitrate,for example, is represented by the formula:NH\ C( NH,)*NH-N H-NEven in this compound it is possible to discern in the three doublelinkings a certain analogy to the aromatic diazonium salts.A further extension of the hypothesis that the diazotisability ofan amine depends on the presence in its molecule of an unsaturatedgroup may be put forward to explain why the tendency t o formdiazonium salts is greatest among aromatic amines.I n the aromatic series, unsaturation of the hydrocarbon radicleis due to the fourth valency of each carbon atom of a six-memberedring. In the diazonium complex, three valencies of one of the twonitrogen atoms are employed its follows: one furnishes the attach-ment to an acid radicle; another links the diazegroup with acarbon atom of the ring; and the third forms one of the bonds ofattachment t o the second nitrogen atom.Regarding nitrogen asalways potentially quinquevalent, an assumption which is justifiedby the position of this element in the periodic classification, thenthe diazonium complex itself, like the aromatic nucleus, has alsoan unsaturation represented by six valencies. These two sets of sixvalencies, representing respectively the residual affinities of thearomatic and diazonium complexes, are indicated by dotted lines informulze V and VI, the first of which is the well-known centricformula :I c1NO,*N,*NH*C( :NH)>N.N,C1(V. 1 (VI. 1The authors’ view is that maximum stability of the diazonium saltresults when the residual affinities of the organic radicle and thediazonium complex satisfy each other to the fullest extent. I n anaromatic monodiazonium salt, the residual affiity of the diazo-groupis available for saturating the six fourth valencies of the aromaticring.This conception of the constitution of diazonium salts suggests,also, an explanation of the following facts: (1) the relativeinstability of the bisdiazonium salts of homonuclear aromaticdiamines ; (2) the difficulty sometimes experienced in diazotisingcompletely the salts of these diamines2564 MCKENZIE AND CLOUGH: EXPERIMENTS ON THEThe authors desire to express their thanks to the Research GrantCommittees of the Royal Society and Chemical Society for grantswhich have partly defrayed the expenses of this investigation.ROYAL COLLEGE OF SCIENCE, LONDON,SOUTH KENSINGTON, S. W