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NITRATION AGENTS AND METHODS MORE RARELY USED 99

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Numerous experiments on the action of nitrogen dioxides on olefins were car-

ried out by Demyanov and Sidorenlco [76] between 1909 and 1934. They obtained

products of the types IIa and III.

Schaarschmidt and Hoffmeier [40] found that on treating unsaturated hydro-

carbon with N 2 O 4 a mixture of products of the I, II, III, and IV types was obtained.

Only the dinitro compounds of type III were stable. Others underwent decom-

position in the following way:

I Nitrosoolefin Nitroolefin

IIb Nitroolefin

IV Unstable nitrite

It was originally thought that the addition of dinitrogen tetroxide to the double

bond of an olefin in a weakly basic solvent such as ether is a heterolytic (ionic

-NO 2

+

NO 2

• ) addition.
  Results of recent study, however, have been interpreted in terms of a homo-
  lytic process. Schechter and Conrad [49] have observed that the production of
  methyl-3-nitroacrylate and methyl-2-hydroxy-3-nitropropionate in the reaction
  between N 2 O 4 and methyl acrylate could not be explained on the basis of hetero-

lytic addition, but was to be expected if a homolytic process were occurring.

Brown [80] has shown that olefin nitration under circumstances in which the

nitronium ion (NO 2

• ) is the reactant has characteristics entirely different from those
  of the N 2 O 4 -olefin reaction. Brand and I. D. R. Stevens [81] also believed the
  reaction of addition of nitrogen dioxide to olefins to involve radicals. According
  to these authors the following experimental facts provide evidence for this:
  (1) Cyclohexene reacted with dinitrogen tetroxide (N 2 O 4 ) to yield l,2-dinitro-
  cyclohexane and 2-nitrocyclohexyl nitrite.

(2) However, in the presence of two moles of bromotrichloromethane the re-

action followed a different course, and the normal products, 1,2-dinitrocyclo-