urbaf2

126 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

NITRATION UNDER INFLUENCE OF GAMMA RADIATION

It has recently been found by Mint and his co-workers [185] that nitration of

benzene occurs when benzene in an aqueous solution of calcium nitrate is

irradiated with gamma rays. The yield is up to 45% of nitrobenzene and a certain

amount of picric acid is also formed. Mint suggested the formation of the nitronium

ion. through the following sequence of reactions:

NO 3 - + H -> NO 2 - + OH -> NO 2 + OH- (a)

NO 2 + OH -> NO 2 + + OH- (b)

Nitration would proceed as (c) in accordance with the radical mechanism or

as (d) assuming an ionic mechanism:

*C 6 H 5 + NO 2 -> C 6 H 5 NO 2

C 6 H 6 + NO 2 + -> C 6 H 5 O 2 + H+

(c)

(d)

The radical, *C 6 H 5 , would be formed through the reaction between benzene and

OH or HO 2 radicals.

Falecki, Mint, Slebodziliski and T. Urbanski, [185a] have also found that

paraffin hydrocarbons dissolved in dinitrogen tetroxide are nitrated at 28°C when

they are subjected to irradiation with gamma rays. The yield for n-hexane was

up to 15% of non-gaseous products of both nitration and oxidation. The charac-

teristic feature of the reaction differentiating it from nitration at elevated tempera-

ture described above (p. 94) is the fact that no pyrolysis of the hydrocarbon occurs,

and therefore long chain paraffins are not so readily split into shorter fragments

as it occurs at high temperature. The authors also found that n-hexane reacts with

dinitrogen tetroxide at 28°C without irradiation. However, the yield of non-gaseous

products is lower (ca. 8%) and the products containing nitrogen are mainly nitrous

esters. This would suggest that N 2 O 4 probably forms ions NO 2

+

or *NO 2 radicals

under the action of irradiation. Without irradiation a considerable amount of

nitrite ions ONO

• are present and these are responsible for the formation of
  nitrous esters.

INDIRECT METHODS OF INTRODUCING A NITRO GROUP

It has already been mentioned (p. 5) that indirect methods of introducing

a nitro group are used in many cases.

SUBSTITUTION OF SULPHONIC GROUPS

Sulphonation of compounds followed by substituting the sulpho group by

a nitro group is the method of great practical importance. This method is widely

used for the nitration of phenols. The reaction occurs as follows:

(84)