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NITRATION AGENTS AND METHODS MORE RARELY USED 125

Apart from this, other, more complex side reactions take place, involving oxidation-

reduction processes and a complete decomposition of the substance with the forma-
tion of nitrite and CO 2 (E. Schmidt [183]) :

C(NO 2 ) 4 + 6KOH -> 4KNO 2 + K 2 CO 3 + 3 H 2 O

The main reaction may be expressed by the equation:

(80b)

C(NO 2 ) 4 + KOH -> KC(NO 2 ) 3 + HNO 3 (80c)

in which the transient formation of nitric acid is acknowledged.

Nitration with tetranitromethane is carried out mostly in the presence of pyri-

dine which with nitroform forms a crystalline addition product.

Hexanitroethane may be used as a nitrating agent in a similar way (for example,

Alsop and Kenner [184]).

Nitroguanidine

Davis and Abrams [184a] have observed that aromatic compounds easy to

nitrate such as phenol, acetanilide, etc. can be nitrated by a freshly prepared solution

of nitroguanidine in sulphuric acid.

There is no evidence that a solution of nitroguanidine in sulphuric acid con-

tains free nitric acid, although the solution turns diphenylamine blue and reacts

with mercury, thus behaving identically like nitric acid. It is estimated that nitric

acid can be formed only in the presence of compounds that are readily nitrated.

According to this view, nitroguanidine decomposes in the presence of sulphuric

acid to give nitramine (eqn. 81), which is hydrolysed in the presence of substances

convertible to nitro compounds to form ammonia and nitric acid (eqn. 81):

NH 2 -C-NHNO 2 -> NH 2 NO 2 + NH 2 CN

II (81)

NH

NH 2 NO 2 + H 2 O -> NH 3 + HNO 3 (82)

The presence of cyanamide, NH 2 CN, in the solution after nitration, as stated by

Davis and Abrams, may serve as evidence confirming the above view.

More convincing, however, is the hypothesis that in nitroguanidine, under the

influence of sulphuric acid, a loosening of the nitrogen atoms bond takes place,

and a nitro group in the form of a nitronium ion breaks off:

NH 2 -C-NH-NO 2 -> NH 2 -C-NH- + NO 2 +

II II (83)

NH NH

Some of the primary nitramines have similar properties and can act as nitrating

agents. However, no systematic studies on the subject have been reported in the
literature as yet.