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60 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

From bornylene they obtained isoborneol (V) and epiborneol (VI) nitrates:

H. Kuczynski and L. Kuczynski have also studied the action of nitric acid

on β− and δ− fenchene, limonene, sylvestrene and other terpene hydrocarbons.

It has also been shown that the addition of nitric acid molecules to olefins is

not the only possible reaction of olefins with HNO 3. Formation of nitro-olefins,

i.e. ordinary nitration by substitution, is also likely. This is discussed later

(p. 81).

NITRATION AS A DOUBLE EXCHANGE REACTION

At present it is generally accepted that the nitration reaction is a double ex-

change reaction. The nitro group becomes attached to one of the carbons in an

aromatic ring, while simultaneously an atom of hydrogen initially connected with

an atom of carbon, is split off as a proton:

(22)

A nitration mechanism formula of this type was suggested by Ingold [28] in 1935.

In 1946, Dewar [29] gave the following mechanism for the double exchange
with the nitracidium ion taking part:

B is a proton acceptor (e.g. the OH- or HSO 4 - ions).

Benford and Ingold [30] pointed out in 1938 that the efficiency of bromination
with a brominating agent of the general formula X-Br depended on the affinity

of X for the electrons of the X-Br bond. It is known, for example, that Cl.Br is
a better brominating agent than Br.Br. Likewise the efficiency of a nitrating agent,

X-NO 2 , depends on the affinity of X for electrons.