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NITRO DERIVATIVES OF ANILINE 567

TETRANITROCARBAZOLE

There are two isomeric tetranitrocarbazoles: 1,3,6,8- (I) (m.p. 296°C) and

1,2,6,8- (II) (m.p. 153-154°C).

I I-I

They are usually prepared by the direct nitration of carbazole with a mixture

of nitric and sulphuric (or acetic) acid. The most convenient way of nitrating car-

bazole is sulphonation followed by the action of concentrated nitric acid. 1,3,6,8-

Tetranitrocarbazole (I) is obtained as the principal product.

The following intermediate products have been isolated in the course of the

nitration of carbazole :

m. p. 210°C m. p. 320°C

In addition to the 1,3,6,8-isomer a product, named by Ciamician and Silber

the γ− isomer, has been obtained, which, according to recent investigations, has

proved to be the 1,2,6,8-isomer (II). From the reaction product pure compound

I may be isolated by extraction with toluene, followed by crystallization from acetic

acid. The pure product I may also be obtained by treating the crude product with

sodium sulphite. According to Murphy, Schwartz, Picard and Kaufman [34], the

melting point of the product may be raised in this way from 278° to 296°C at
the cost of a 10% loss of yield. The same authors found that during the nitration

process the 1,2,6,8-isomer (II) is formed along with the principal product. This

isomer may be obtained in a larger quantity if carbzole is subjected to sulphona-

tion with oleum prior to nitration.

The constitution of tetranitrocarbazole (I) was determined by Borsche and

Scholten [35] from the following reactions, of which the final stage was the formation