532 POPE: COLOUH. AND CONSTITUTION OF

XLIX. - cozou?l and Constitution of Axomethine Compounds. Part I. By FRANK GEORGE POPE.

IN a paper recently communicated to the Society by Hewitt and Mitchell (Trans., 1907, 91, 1251), i t was shown tha t the nitroazo- phenols and naphthols on treatment with alkalis gave salts, which in the case of the para-nitrated compounds exhibit absorptions of a type radically different from tha t shown by the phenol or naphthol itself, except where a group has been introduced into the molecule which, by virtue of its character and position, prevents the formation of a di- quinonoid structure. The authors, considering that a change in the absorption spectrum of a compound when it undergoes transformation into a salt generally points to a radical alteration of constitution, formulate the free azophenols and their alkali salts as follows :

Since the azomethine (*N:CH*) grouping shows a considerable likeness to the azo- (*N:N*) grouping in many respects, it seemed probable tha t a similar change might be observed in the compounds where such a grouping existed, and this investigation was undertaken to ascertain if such were the case. Very little appears in the current chemical literature concerning the difference between the azomethine compounds and their salts. Rlohlau (Rer., 1898, 31, 2260) has prepared such compounds by the condensation of 5 -aminosalicylic acid and the three nitrobenzaldehydes, and has noted that the substances are yellow, and, in the case of the ortho- and para-nitro-compounds, give orange-yellow solutions with sodium hydroxide. Sachs (Ber., 1907, 40, 3230) has also prepared similar compounds by condensing 2 : 4-dinitrobenzaldehyde with various aminonaphthols, and has noted tha t in the cases of the 4 : 1-, 5 : 1-, and 8 : 2-aminonaphthols, on the addition of a caustic alkali, the solutions become deep blue or violet, the free anhydro-substances giving reddish-brown or orange-red solutions in alcohol.

It was found during the course of the present investigation tha t the absorption spectra of the free azomethine compounds and of their alkali salts were very different in character, and consequently the same assumption is made in the case of the nitrated azomethine compounds as i n that of the similarly constituted nitroazophenols, namely, that the transformation of the nitroazomethine structure to the isonitroisoazomethine form is accompanied by a change in the oscillation-frequency of the molecule ; absorption bands appear in the

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AZOMETHINE COMPOUNDS. PART I. 533

violet or blue end of the spectrum with the result that the solutions appear red or reddish-brown by transmitted light. This is rendered clear by comparing the absorptions of benzylidene-p-aminophenol and 4-nitrobenzylidene-p-aminophenol. I n alcoholic solution (N/ loo), the violet and blue are absorbed as far as wave-lengths 455 and 482 pp respectively, but, on the addition of potassium hydroxide, the solution of the former shows absorption extending as far as 473 pp and the latter as far as 622 pp, being continuous from the ultra-violet into the visible spectrum ; moreover, the solution changes from pale orange- yellow to a deep reddish-brown. The potassium salts of these compounds may thus be represented as :

It is t o be noted that Sachs’ 2’ : 4’-dinitrobenzylidene-4-amino-a- naphthol, like p-nitrobenzeneazo-a-naphthol (Meldola, Trans., 1885, 47, 661; Bamberger, Ber., 1895, 28, 848), forms reddish-brown crystals, and gives a deep blue alkaline solution. Consequently, the following formula may be suggested for this compound :

NO2 \ /

\-/ \-/ o,N/-\cH:N/-\oH -+ KO,N

and similar fo rmuh for the compounds derived from the 5 : 1- and 8 : 2-aminonaphthols, since it is in these positions in the naphthalene nucleus where the possibility of a quinonoid structure is apparent, and, in the 5 : 2- and 7 : 2-aminonaphthol compounds where such a structure is precluded, Sachs found that the solutions in alkali were dark red.

E X P E R I M E N T A L .

Benaylidene - p -aminophenol, /-\cH:N/-\oH. \-/ \-/ This substance has been previously prepared by Philip (Bey . , 1892,

26, 3248), the melting point being given as 181’. On preparing it by condensing the components in dilute acetic acid, and recrystallising the product from alcohol, it separated in almost colourless needles, melting sharply at 1 8 3 O . It gives an almost colourless solution in alcohol, which becomes slightly darker (very faintly yellow) on the addition of alkali.

p-Nitro benxylidene-p-aminopheno I, NO,/-\CH :”-\OH. \-/ \-/ Equivalent weights of p-nitrobenzaldehyde and of p-aminophenol

were separately dissolved in dilute acetic acid, the solutions inixed

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534 POPE: COLOUR AND CONSTITUTION OF

and allowed to stand for some time. The resulting precipitate was crystallised from alcohol, from which small, yellowish-brown needles separated, melting a t 168.5'. The substance gives an orange-yellow solution in alcohol, which, on the addition of alkali, becomes a deep orange-red :

0,1612 gave 0.3793 CO, and 0.0627 H,O. C = 6 4 * 1 7 ; H = 4 ~ 3 2 . Cl,H1,O,N, requires C = 64-46 ; H = 4.13 per cent.

013 p-NitrobenzyZidene-o-amiizoplAenoZ, NO, /-\CH:N/-\

\-/ \-/ This compound was prepared by dissolving equivalent weights of

p-nitrobenzaldehyde and o-aminophenol separately in absolute alcohol and mixing the solutions. Tufts of needles separated after a short time. The compound was precipitated by water and crystallised from alcohol, being obtained in brownish-yellow needles, meltiiig at 1 6 1 O . I t s solution in alcohol is yellow, and on the addition of alkali becomes orange-red :

0 9 0 9 4 gave 0,4949 CO, and 0.0794 H,O. C: = 64.46 ; H = 4.21. Cl3HlOO3N2 requires C = 64.46 ; H = 4-13 per cent.

p-~itrobenxy~idene-5-aminosa~icy~ic acid, NO,/-\CH:N/-\OH CO,H

\-/ \-/ '

Considerable difficulty was experienced in preparing this substance by the method given by Mohlau (Zoc. c i t . ) , since it was found that a residue containing sodium salts was always left after combustion. The difficulty was overcome by the addition of a small quantity of acetic acid to the solution of 5-aminosalicylic acid hydrochloride in alcohol, and then adding to this the solution of p-nitrobenzaldehyde in alcohol (containing the required amount of sodium acetate). The product separated in a few minutes as a brownish-yellow solid, which, when crystallised from dilute alcohol, in which it is somewhat sparingly soluble, melted (with decomposition) at 245-247' (Mohlau gives 217-218'). Its solution in alcohol is very pale yellow, and on the addition of alkali it becomes dark brown. The acid gives brown coloured salts with heavy metals :

0.1952 gave 0.4193 CO, and 0.0654 H,O. C = 58.58 ; H = 3.72. C,,Hl,O,N, requires C = 58.74 ; H = 3.50 per cent.

NO, /-\cH: N/-\oH, was \-/ \-/ m-Nitrobe?z~?/Zidene-p-anzino),!lenol,

prepared by mixing equivalent qu;tnt:i ties of the components in warm

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AZOMETHINE COMPOUNDS. PART I. 535

dilute acetic acid. After some time the solution was poured into water, and precipitate crystallised, first from dilute acetic acid and finally from dilute alcohol. It separates in small, brown needles, which melt a t 154'. I t s alcoholic solution is pale yellow, and on the addition of alkali becomes slightly darker in shade :

0.1992 gave 0-4673 CO, and 0.0763 H,O. C = 63-98 ; H = 4.26. C13Hlo03N2 requires C = 64.46 ; H = 4-13 per cent.

NO, O H rn-Nitrobenzylidei2e-o-nniinopheno2, /L\OH:N<I)I was obtained \-/

by condensing its components in absolute alcoholic solution. After a short time the solution was poured into water, and the precipitate crystallised from alcohol, from which it separated in fine, pale yellow, felted needles, melting a t 135'. Its alcoholic solution is pale yellow, and on the addition of alkali becomes slightly darker in shade :

gave 0.4378 CO, and 0.0729 H,O. CI,H,,03N, requires C = 64.46 ; H = 4.13 per cent.

C = 63.71 ; H = 4.33. 0.1874

OH

This compound has been prepared by Emmerich (Annalen, 1887, 241, 344) and Duparc, Annalen, 1891, 266, 140). It crystallises in pale yellow needles, and its alcoholic solution is pale yellow. On the addition of alkali t o this no visible change was observed. Since the sodium salt of this compound shows less absorption than the free azo- methine (see table), it might be suggested tha t the anhydro-compound in this case possesses a quinonoid structure and is to be formulated as

?.

O H

o-Hydroxybenxy&idene-p-nitroan2ine, /-\CH:N/-\NO, \-/ \-/ - This compound has been previously prepared by Haarman (Bey.,

1873, 6, 339), and is described as melting at 115'. By dissolving equimolecular quantities of salicylaldehyde and p-nitroaniline separately in dilute acetic acid, and mixing the solutions, a deep orange pre- cipitate was obtained, which crystallised from dilute acetic acid in small needles melting a t 159'. The preparation was repeated, and the same result was obtained, and a mixture of the two preparations also melted sharply at 159". The substance dissolves in alcohol

VOL. XCIII. N N

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536 POPE: COLOUR AND CONSTITUTION OF

readily, and the dilute solution is pale yellow, but on the addition of alkali becomes reddish-brown in shade :

0.1636 gave 0.3843 CO, and 0.0634 H20. C = 64.07 ; H = 4.30. Cl,H[,,O,N, requires C = 64.46 ; H = 4.13 per cent,

OH NO2

\-/ \-/ o-liydroxybenxylidene-m-nitroaniline, /-\CH:N/-\ was pre-

pared by mixing equimolecular quantities of its components in dilute alcoholic solution. The resulting crystalline magma was filtered, and the substance recrystallised from absolute alcohol, from which it separated in pale yellow needles, melting at 132’. The alcoholic solution is pale yellow, and the solution remains practically unchanged on the addition of alkali :

0,2020 gave 0.4794 CO, and 0.079 H,O. C = 64.72 ; H=4*35. C13H1003N2 requires C = 64-46 ; H = 4.13 per cent.

p- NitrobenxyZidene-4-arnino-a-nclpl~thol, 02N

has been prepared by Mohlau (loc. c i t . ) . It crystallises in red needles or plates and the alcoholic solution on the addition of alkali becomes violet.

So far as the spectroscopic observations are concerned, only the visible portion of the spectrum has been examined. The solutions examined were alcoholic, solutions of the sodium salts being prepared by adding a drop of 40 per cent. sodium hydroxide solution to the parent substance. The statement (‘ From 528 pp onwards,” means that from 528 pp onwards the blue and violet are absorbed as far as the visible spectrum extends.

Absorption. Substance. Concentration. (Red). (Violet).

(>CH:N<>OH ..................

(->cH:N<-)oN.. .................

NO/-\CH:N<~>H ............ - -

\-/ N~o,N:/-\*cH.N:’”-\:o ......

NO,/-\CH: NQ.. ................

N;IO,N://’=\:CH-N:(_) \=/ .........

\-/- \-/ OH

\-/ 0 ..

N/lOO 9 ) 533 PP ¶ >

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AZOMETHJNE COMPOUNDS. PANT I. 537

Absorption. Substance. Concentration. (Red). (Violet).

NO~(~)CH:N(;>:OH ............ CO,H

N~O,N:(-):CH*N:<:):O - ...... C0,Na

NO,

NO,

\C H : N<->H ..................

/-\CH:N(I>ONa .................

-

\-/ NO2 OH /-\CH:N/-\ \-,/ ,-/ .......................

/-\cH:N/-\ \-/ \ / ........................ NO, ONa

- OH

\-/ /-\CH:N<II)NO, .................. 0

/ -: CH *N : /-\* N 0,Na ........ \-/ \-/*

0 I3 NO2 (I>cH :N( 7). .......................

0 13 O C H : .(I>. ......................

ONa <I)CH:N(I> ........................

............

\-

N/lOOO

A'/lOOO

N/lOO

N/100

N/lOO

N/lOO

N/100

N/lOO

N/lOO

N/lOO

N/100

N/lOO

N / 5 0 0 0

N/5000

From 457 p p onwards

9 9 5 0 0 P P 9 )

Band 577 t o 465 p,t~

I have to thank the Research Fund Committee for a grant which has partly defrayed the expense of this work.

EAST LONDON COLLEGE.

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