364 HEWITT, JOHNSON AND POPE: THE ABSORPTIONXXX1X.-The Absorption 8pectq.a of Nitrated Phenyl-h ydrazones.Ry JOHN THEODORE HEWITT, RHODA MARIANNE JOHNSON, andFRANK GEORGE POPE.SOME few years ago Baly and Tuck (T., 1906, 89, 982) describedthe absorption spectra of a number of aldehydic and ketonic phenyl-hydrazones, and drew attention to the colour shown by several ofthe nitro-derivatives. It was suggested (Zoc. cit., p. 996) thaSPECTRA OF NITRATED PHENYLHYDRAZONES. 365possibly p-nitrobenzaldehydephenylhydrazone does not possess theformula I, but is to be represented with a quinonoid structure (11) :NO,*C,H,*CH:N*N H*C6H5 HO O>N:(>:C:N~NH-C,H,(1.1 (11.1Certain pnitrophenylhydrazones with which we were occupiedattracted our attention owing to the remarkable colour changesproduced when alkalis were added to their alcoholic solutibns; infact, some of these compounds possess distinctly acidic properties.The great difference in colour between the compounds themselvesand their salts led to the view that there was probably a con-stitutional difference.I f such difference actually exists, the quinonoid formula wouldprobably be assignable to the salt, and the conventional hydrazoneformula to the hydrogen compound; although for the latter anotherstructure is not impossible.The most promising way of obtaining evidence of the characterdesired is to compare the spectra of benzaldehyde-pnitrophenyl-hydrazone in neutral and in alkaline solution with that of pnitro-benzaldehydephenylhydrazone, and, further, to examine the extentto which colour changes are inhibited by replacement of thehydrogen atoms marked with an asterisk in the formulze: * * * *C,H,* CH *N*NH* C,H,-NO, NO,.C,H4* CHON -NH *C,H5when the solutions were rendered alkaline.phenylhydrazone would be represented by the formula :the diminution in oscillation frequency occurring on salt formation,accompanying the greater length of chain of conjugated doublelinkings.Comparison of Figs. 1 and 2 will show that, as might be expected,the p-nitrophenylhydrazones of benzaldehyde and of acetophenonegive practically identical absorption spectra, and further, thateach, when converted into a salt, shows practically the same shift inits absorption.According to our view, the sodium salt of benzaldehyde-p-nitroC6H5*CH:NoN: C6H4:NO$?a,I n fact, the pairs of formulae:andC6H5>C: N*N:C6H,:N0,Na.CH3',%>C:N*N :C6H,:NO2Naare .strictly comparable.Baly and Tuck showed that the absorption spectra of the phenyl-hydrazone and of the phenylmethylhydrazone of p-nitrobenz366 HEWITT, JOHNSON, AND POPE: THE ABSOBPTIONaldehyde were practically identical (Zoc. cit., p.996), and it isinteresting to note that the head of the band in the visible spectrumlies a t very much the same position as that of the band shown by thepnitrophenylhydrazones of benzaldehyde and of acetophenone.The addition of alkali hydroxidev to yellow alcoholic solutionsof the pnitrophenylhydrazones of benzaldehyde and acetophenonecauses the colour to change to red of very similar shade to magenta,Relative thicknesses in mm.of N/10,000-solulion.0mo m m a0 0 rl0 0 o m m e 4000 TI,0M ' gd G ga$% ;%%re.&& * g - s s'G 8 , c ; s f .s * ?.s e.4.Sei f g &$Q g 3" QQ.s 0 &X B . g x %SSS0 u g-4 h e 3 .p5I .3 0e b e b6 1 % ;a+000 *0' 02 , o Fr000 CJ? 7 9 900 407 P 9 4 0.~ozlnlos-0 00 '0 I INa a CJ m r( rl r( rl r( 040 'urn ue sassaulyqyp anzpqai so s z u y j y ~ b o ~and the maximum coloration is produced by a medium amount ofthe alkali. In the caw of the equally yellow solution of p-nitro-benzaldehydephenylhydrazone, as alkali is progressively added, nocolour change is a t first observed; a large excess produces adeepening of shade, but not a change of colour.These facts agreewith our view that the compounds contain the grouping *CH:Na,tor whilst the change of structure from the grouping represented bSPECTRA OF NITRATED PHENYLHYDRAZONES. 36'1NO,*C,H,-NH~ to KNO,:C,H,:N* seems to be fairly common, casesof such a change as N0,*C6H4*CUH: to KNO,:C,H,:C: orK",:C,H,:CH- are comparatively rare.The spectrum of pnitrobenzaldehydeplienylhydrazone is given inFig. 3; the curve differs slightly from that of Baly and Tuck, butthe head of the band in the visible spectrum will be found a t almostexactly the same persistence and oscillation frequency, namely,2350.Now, whilst Baly and Tuck show that both the phenylhydrazoneand the phenylmethylhydrazone of p-nitrobenzaldehyde givevirtually identical absorption spectra, it will be seen on referenceto Fig.3 that replacement of the hydrogen atom marked *NO,. C6&*cH:NmN&o C6H5,by acetyl instead of methyl shifts the absorption strongly towardsthe ultra-violet. One may compare this shift in the absorptionwith that accompanying the conversion of aniline into acetanilide.We have mentioned earlier that the hydrazones dealt with in thispaper are better represented by the conventional than by quinonoidformulae; a t the same time we remarked that a different constitutionwas not impossible. Thus, benzaldehyde-(pnitrophenylhydrazonemight possess an internal salt structure:C,H,*CH:N*NH:C,H,:N:OI .L - - O ,in fact, (pnitrophenylhydrazine itself might be :H,N* NH:C,H,:N:O1 6Baly and Tuck (Zoc. cit., p. 997) drew attention to the greatdifference in the absorption spectra of the pnitro- and pbromo-derivatives of phenylhydrazine ; further than this, Borsche(Annded, 1907, 357, 171) has shown that quinones of the benzeneseries react with o-nitro- and 2 : 4-dinitro-phenylhydrazines withformation of hydroxyazo-compounds, whereas phenylhydrazine itselfis oxidised in these circumstances. Borsche himself (lot. tit., 173,footnofe) suggests that o-nitrophenylhydrazine may possess thestructure :/='\:N-NH,, \JNO,HWhereby this behaviour would be accounted for. The wholequestion as to whether many nitroamino-derivatives may not possessan internal quinonoid d t structure requires further work368 DUNNINGHAM : THE SYSTEM : ETHYL ETHER-WATER-I n conclusion, we desire to express our thanks to the ResearchFund Committee of the East London College for a grant defrayingthe costs of the investigation.EAST LONI~ON COLLIWE.UNIVEKSI.I'Y OF LONDON