urbaf2

NITRATION AGENTS AND METHODS MORE RARELY USED 117

On the basis of Arnall’s experiments, Zawidzki [147] had deduced the follow-
ing equation for the rate of phenol nitration:

where x is the concentration of nitrophenol just being formed; a, b, c are the initial

concentrations of phenol, nitric acid and nitrous acid respectively: (a-x), (b-x),

(c-x) are the concentrations of these compounds after the lapse of time t. The

reaction rate constant equals k = ca. 0.043.

Klemenc and Schüller [148] have derived the following formula for the rate

of nitration (v) with nitric acid:

V = k[HNO 3 ]5/2 [HNO2]½c^2

where c is the concentration of the compound being nitrated.
It can be seen from this equation that nitrous acid as an agent increasing the

reaction rate is of great importance.

Kartashev [149] has investigated the reaction of phenol with nitric acid in de-

tail. The author assumes the mechanism of the nitration of phenol with nitric acid

to be as follows:

(1) In the first stage nitric acid oxidizes phenol and forms nitrous acid.

(2) Nitrous acid reacts with phenol to form nitrosophenol.

(3) Nitrosophenol is oxidized by nitric acid to nitrophenol forming again new

quantities of nitrous acid.

HNO 3 -> HNO 2 + O (64)

(65)

(66)

It has been shown that the addition of nitrous acid lowers the initiation tem-

perature of the reaction; the addition of p- nitrosophenol affects the reaction in
a similar way. The addition of urea to nitric acid results in lowering the reaction

rate. A similar nitration scheme was given by Veibel [150].