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86 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

ELECTROLYTIC NITRATION

Electrolytic nitration was first proposed by Triller [22] in 1897. This author

pointed out that with nitric acid of concentration 52% HNO 3 at 80°C α− nitro-

naphthalene free from dinitronaphthalene can be obtained at the anode. With

nitric acid of concentration 65% HNO 3 dinitronaphthalene is obtained. Fichter

and Plüss [23] checked the Triller’s patent in 1931 by carrying out simultaneous

experiments with ordinary and electrolytic nitration. They found that the electro-

lytic method did indeed provide higher yields of α− nitronaphthalene. But the authors

believed this was due not to a higher concentration of nitric acid (or more exactly

of NO 3 - ions) at the anode, but rather to a rise of temperature over this area. Con-

trary to this view, Calhane and Wilson [24] came to the conclusion that it was

the formation of a layer of high concentration around the anode that accounted

for the increase in the yield.

Kirk and Brandt [25] nitrated toluene with a mixture of nitric and sulphuric

acids both by the usual method and by the simultaneous use of the electrolytic

method and found that with the latter technique higher yields could be obtained.

Atanasiu and Belcot [26,27] treated aromatic hydrocarbons with a much dilute

nitric acid (at a concentration insufficient for nitration) and, due to the electro-

lysis, which they carried out simultaneously, they succeeded in obtaining nitration

in the anode area. In studying the reaction they observed particularly vigorous

oxidation processes.

Edwards [28] carried out experiments in 1950 comparing the nitration of toluene

under ordinary conditions with that combined with simultaneous electrolysis and

found that higher yields of nitro compounds resulted when electrolysis was applied.

NITRATION WITH NITRIC ACID VAPOUR

The nitration of aliphatic hydrocarbons may be accomplished in the vapour

phase, at 410-430°C, using nitric acid vapour. A number of papers describing

this method of nitration were published by Hass and co-workers [29] between

1936 and 1940.

Under the influence of a high temperature during the reaction the hydrocarbon

chain is split off to give shorter ones and such compounds as nitromethane and

nitroethane are formed. For example, the authors obtained the following products

in the nitration of n-pentane at 400°C:

nitromethane 1.1%

nitroethane 7.2%

1-nitropropane 13.8%

1-nitrobutane 12.5%

1-nitropentane 20.6%

2-nitropentane 20.8%

3-nitropentane 23.0%

Higher temperature enhances the formation of nitroparaffins with shorter chains.