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214 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

The mobile electron is most likely that associated with the free valency on the

N atom.

INHIBITING ACTION OF NITRO COMPOUNDS ON POLYMERIZATION

Another example of the homolytic reaction of nitro compounds with free

radicals is their inhibiting effect on addition polymerization of vinyl compounds,

especially by the higher nitrated compounds which have the most pronounced inhib-

iting properties.

This property of nitro compounds was first observed by Foord [78] with regard

to o- nitrophenol, 2,4-dinitrophenol, picric acid, m- dinitrobenzene, 2,4-dinitro-

toluene, 1,3,8-trinitronaphthalene, 2,4-dinitroaniline and other higher nitrated

aromatic compounds.

Subsequently Price and Durham [79] stated their view regarding the inhibition

of polymerization, which, according to them, consisted in a free radical reaction,

analogous to the reaction of alkylation of trinitrobenzene, discovered by Fieser

and his co-workers [71a], which has already been described. Price [80] suggested

the following mechanism for the reaction, assuming that two molecules I and II

were formed from a polymerizable radical k:

I II

However, Bartlett and his co-workers [81,82] provided evidence, based on the

study of the reaction kinetics, which proved that inhibition of polymerization

started at the oxygen atom of a nitro group:

(35a)

(35b)