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CHAPTER I

NITRATION AND NITRATING AGENTS

GENERAL INFORMATION

NITRATION is one of the earliest known organic chemical reactions. It is mentioned

in the writings of the alchemists. As early as in the first half of the XVIIIth century

Glauber obtained picric acid by acting on wool and horn with nitric acid. Soon

reactions between nitric acid and a variety of organic substances became one of

the alchemical reactions most frequently used. They were usually carried out by

heating a substance with nitric acid, often to boiling point. Thus picric acid was

obtained from certain organic substances such as indigo, silk, resins, etc.
In 1833 Braconnot obtained nitric esters of cellulose and starch by acting with

nitric acid on plant fibres and starch, at low temperature. In 1834 Mitscherlich

nitrated benzene to nitrobenzene. But it is only since 1842, when Zinin reduced

nitrobenzene to aniline, that rapid development of the chemistry of nitro compounds

and their application to organic industry has occurred.

At present nitration is one of the most widely applied direct substitution re-

actions. This is due to several factors. For example nitration usually proceeds

easily, its products can readily be separated from the spent acid, and there is a wide
range of possibilities in the practical use of nitro compounds, both as intermediates

and end products. The presence of a nitro group in the starting product made it

possible to obtain a number of basic organic intermediates such as aniline and

benzidine. Dyes with more than one nitro group, such as picric acid were obtained.

It has been found that higher nitrated nitro compounds and nitric acid esters

have explosive properties and are of practical importance. Some nitro compounds

are used in perfumes. Medicinal properties have lately been discovered in certain

nitro compounds, e.g. chloramphenicol.
Nitration is a reaction which has contributed greatly to the development of the

substitution rule [I]. Although nitration had been well known and widely used

for many years both in the laboratory and in industry, little was known about
the nature and mechanism of this reaction until recently. However, in the last two

decades much progress has been made in this field.
With the aid of the new techniques offered by modem physics and physical

chemistry and by the application of the modem electronic theory of chemical bonds,