urbaf2

NITRATION AGENTS AND METHODS MORE RARELY USED^111

Zakharov [126] criticized Desvergnes’s view, which he considered to be in-

exact in a number of points.

On the basis of his own experiments, Zakharov suggested a different mechanism

of reaction. He believed that the catalyst initially weakens the stability of the aromatic

ring by the rupture of a double bond on the attachment of mercuric nitrate, e.g.:

(48)

Nitrobenzene would be formed as result of the following reaction:

(49)

Zakharov found oxynitration to proceed best at 60% concentration of nitric acid.

Davis [127,128] and later Blechta and Patek [129] found that as a result of

nitrating toluene in the presence of mercuric nitrate, besides nitrotoluenes, trinitro-

m- cresol and p- nitrobenzoic acid could also be obtained. The authors explained

the mechanism of the reaction by assuming the formation of toluene and the mercury

salt complex to be the first stage. On decomposition of the complex by the action

of nitric acid, the activated hydrocarbon thus formed was nitrated.

According to Kholevo and Eitington [130] the nitratiton of m- xylene leads

to formation of 4-nitro-3-methylbenzoic acid. Here the mercuric nitrate also en-

hances the oxidation of the methyl group.

Davis and his co-workers [127,128] found chlorobenzene also undergoes oxynitration

by action of 65% nitric acid, with formation of trinitro-m-chlorophenol along with chlo-

ronitrobenzenes, while naphthalene when nitrated with more dilute acid, for example,

at a concentration of 65%, yielded 2,4-dinitro-a-naphthol besides 2-nitro-a-naphthol.

To explain the reaction Davis proposed the following mechanism consistent

in the main with Zakharov’s view referred to above:

(50)