urbaf2

NITRATION AGENTS AND METHODS MORE RARELY USED 89

isomerize to give oximes. The nitrites give lower aldehydes, ketones and lower

radicals which form lower nitro compounds. The alcohols oxidize to aldehydes

and ketones, and the latter to acids, which may yield esters with alcohols. The

nitrates may give off a HNO 3 molecule to form olefins, and the latter may give

dinitro compounds, etc. The nitroso compound formed may subsequently give a

dinitro derivative (Ponzio [35]); for example:

N 2 O 4

C 6 H 5 CH 2 NO -> C 6 H 5 CH=NOH -> C 6 H 5 OH(NO 2 ) 2 (10)

Titov’s experiments have shown that the nitration of alkyl-aromatics may lead

not only to formation of ω− nitro compounds, but of ω− dinitro compounds as well.

McCleary and Degering [36] present a different mechanism for the nitration

of paraffins with the nitric acid vapour, although like Titov they also assume the

formation of free radicals:

RH + (oxidizing agent) -> R. + .H

R. + HONO 2 -> RNO 2 + .OH

RH + .OH -> R. + H 2 O etc. (11)

Yet another mechanism (11) with free radicals taking part has been suggested

by Boord [37]:

HONO 2 -> HO. + .NO 2

RH + HO. -> R. + H 2 O

R. + -NO 2 -> RNO 2 (12)

By analogy with the chlorination mechanism, in which we assume a chain

reaction, Boord also suggests another chain mechanism with repeating links. He

assumes that nitric acid undergoes decomposition at a high temperature to form

nitric anhydride :

2HONO 2 -> NO 2 -O-NO 2 + H 2 O

NO 2 -O-NO 2 -> .NO 2 + .ONO 2

RH + .ONO 2 -> R. + HONO 2

R. + NO 2 -O-NO 2 -> RNO2 + .ONO2 (13)

However, Hass and Riley [38] assume that the nitration of aliphatic hydro-

carbons proceeds through the formation of addition products which subsequently

undergo a breakdown which may (in the case where a certain kind of the addition
product is formed) involve the rupture of C-C bonds:

CH 3 - CH 3 + HNO 3 -> --> CH 3 OH + CH 3 NO 2 (14)