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NITRATION THEORIES 59

Thus, there is evidence that such addition is probable and it seems to confirm the

basic scheme of Thiele-Holleman-Wieland, assuming that under certain conditions

substitution with the NO 2 group may be preceded by the formation of addition products.

Although this view was replaced by the conception of the nitration reaction

as double exchange reaction, it seems that the mechanism of the nitration reaction

is rather a complicated one and under various conditions may proceed differently.

The mechanism which includes addition may also exist, especially at low temperatures,

and may not necessary proceed under the influence of the nitronium ion. It seems

that nitric acid in the form of HO-NO 2 can be the nitrating agent acting through

the addition mechanism.

Studies of the nitration of terpenes are of interest too, as they provide evidence

for the possibility of attaching a HNO 3 molecule to the double bond. Konovalov

[24] obtained nitro derivatives from menthene, camphene, pinene and bornylene

on acting with nitric acid. Bouveault [25] was able to prepare an addition product

of camphene and HNO 3. He obtained an oily product with a structure that could

not be well defined. The reaction of addition of nitric acid to the double bond was

studied in detail by Sucharda [26]. He found that on acting on pinene with nitric

acid containing 33% of KNO 3 instead of with pure nitric acid, or by introducing

nitric acid vapours diluted with dry air, nitric acid esters were obtained in over

70% yield. When reduced with zinc dust in the presence of ammonia, the esters

were converted to the corresponding alcohols.

Using both methods Sucharda obtained: borneol (I), fenchol (II) and terpineol

(III) nitrates :

H. Kuczynski and L. Kuczyliski [27] extended Sucharda’s observations in their

studies on other terpene hydrocarbons. They obtained isoborneol nitrate (IV)

on reacting camphene with concentrated nitric acid (without KNO 3 ):