364 HEWITT, JOHNSON AND POPE: THE ABSORPTION

XXX1X.-The Absorption 8pectq.a of Nitrated Phenyl- h ydrazones.

Ry JOHN THEODORE HEWITT, RHODA MARIANNE JOHNSON, and FRANK GEORGE POPE.

SOME few years ago Baly and Tuck (T., 1906, 89, 982) described the absorption spectra of a number of aldehydic and ketonic phenyl- hydrazones, and drew attention to the colour shown by several of the nitro-derivatives. It was suggested (Zoc. cit., p. 996) that

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SPECTRA OF NITRATED PHENYLHYDRAZONES. 365

possibly p-nitrobenzaldehydephenylhydrazone does not possess the formula 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 (11.1 Certain pnitrophenylhydrazones with which we were occupied

attracted our attention owing to the remarkable colour changes produced when alkalis were added to their alcoholic solutibns; in fact, some of these compounds possess distinctly acidic properties. The great difference in colour between the compounds themselves and their salts led to the view that there was probably a con- stitutional difference.

I f such difference actually exists, the quinonoid formula would probably be assignable to the salt, and the conventional hydrazone formula to the hydrogen compound; although for the latter another structure is not impossible.

The most promising way of obtaining evidence of the character desired 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 extent to which colour changes are inhibited by replacement of the hydrogen atoms marked with an asterisk in the formulze:

* * * * C,H,* CH *N*NH* C,H,-NO, NO,. C,H4* CHON -NH *C,H5

when 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 double linkings.

Comparison of Figs. 1 and 2 will show that, as might be expected, the p-nitrophenylhydrazones of benzaldehyde and of acetophenone give practically identical absorption spectra, and further, that each, when converted into a salt, shows practically the same shift in its absorption.

According to our view, the sodium salt of benzaldehyde-p-nitro

C6H5*CH:NoN: C6H4:NO$?a,

I n fact, the pairs of formulae:

and

C6H5>C: N*N:C6H,:N0,Na. CH3

',%>C:N*N :C6H,:NO2Na

are .strictly comparable. Baly and Tuck showed that the absorption spectra of the phenyl-

hydrazone and of the phenylmethylhydrazone of p-nitrobenz-

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366 HEWITT, JOHNSON, AND POPE: THE ABSOBPTION

aldehyde were practically identical (Zoc. cit., p. 996), and it is interesting to note that the head of the band in the visible spectrum lies a t very much the same position as that of the band shown by the pnitrophenylhydrazones of benzaldehyde and of acetophenone.

The addition of alkali hydroxidev to yellow alcoholic solutions of the pnitrophenylhydrazones of benzaldehyde and acetophenone causes the colour to change to red of very similar shade to magenta,

Relative thicknesses in mm. of N/10,000-solulion. 0 m

o m m a 0 0 rl

0 0 o m m e 4

0 0 0 TI,

0 0

M ' g d G g

a

$ % ;% %re.&& * g - s s

'G 8 , c ; s f . s * ?.s e.4.S

ei f g &$Q g 3" Q Q

.s 0 &X B . g x % S S S 0 u g-4 h e 3 .p5 I .

3 0

e b e b

6 1 % ;a+ 0 0 0 * 0

' 0

2 , o Fr

0 0 0 CJ

? 7 9 900 407 P 9 4 0

. ~oz ln los -0 00 '0 I IN a a CJ m r( rl r( rl r( 0

40 'urn ue sassaulyqyp anzpqai so s z u y j y ~ b o ~

and the maximum coloration is produced by a medium amount of the alkali. I n the caw of the equally yellow solution of p-nitro- benzaldehydephenylhydrazone, as alkali is progressively added, no colour change is a t first observed; a large excess produces a deepening of shade, but not a change of colour. These facts agree with our view that the compounds contain the grouping *CH:Na, tor whilst the change of structure from the grouping represented by

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SPECTRA O F NITRATED PHENYLHYDRAZONES. 36'1

NO,*C,H,-NH~ to KNO,:C,H,:N* seems to be fairly common, cases of such a change as N0,*C6H4*CUH: to KNO,:C,H,:C: or K",:C,H,:CH- are comparatively rare.

The spectrum of pnitrobenzaldehydeplienylhydrazone is given in Fig. 3; the curve differs slightly from that of Baly and Tuck, but the head of the band in the visible spectrum will be found a t almost exactly the same persistence and oscillation frequency, namely, 2350.

Now, whilst Baly and Tuck show that both the phenylhydrazone and the phenylmethylhydrazone of p-nitrobenzaldehyde give virtually identical absorption spectra, it will be seen on reference to Fig. 3 that replacement of the hydrogen atom marked *

NO,. C6&*cH:NmN&o C6H5, by acetyl instead of methyl shifts the absorption strongly towards the ultra-violet. One may compare this shift in the absorption with that accompanying the conversion of aniline into acetanilide.

We have mentioned earlier that the hydrazones dealt with in this paper are better represented by the conventional than by quinonoid formulae; a t the same time we remarked that a different constitution was not impossible. Thus, benzaldehyde-(pnitrophenylhydrazone might possess an internal salt structure:

C,H,*CH:N*NH:C,H,:N:O I .

L - - O , in fact, (pnitrophenylhydrazine itself might be :

H,N* NH:C,H,:N:O 1 6

Baly and Tuck (Zoc. cit., p. 997) drew attention to the great difference 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 benzene series react with o-nitro- and 2 : 4-dinitro-phenylhydrazines with formation of hydroxyazo-compounds, whereas phenylhydrazine itself is oxidised in these circumstances. Borsche himself (lot. tit., 173, footnofe) suggests that o-nitrophenylhydrazine may possess the structure :

/='\:N-NH,, \J NO,H

Whereby this behaviour would be accounted for. The whole question as to whether many nitroamino-derivatives may not possess an internal quinonoid d t structure requires further work.

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368 DUNNINGHAM : THE SYSTEM : ETHYL ETHER-WATER-

I n conclusion, we desire to express our thanks to the Research Fund Committee of the East London College for a grant defraying the costs of the investigation.

EAST L O N I ~ O N COLLIWE. UNIVEKSI.I'Y OF LONDON.

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