urbaf2

536 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

The presence of a large number of hydroxyl groups in the ring increases the

reactivity of phenol very considerably. That is why these compounds are very

easy to nitrate, and in the nitration process by the conventional method for phenols,

i.e. via sulphonation, followed by nitration, three nitro groups usually enter the

compound. This is also the reason why the preparation of, for example, a nitro

derivative of resorcinol with less than three nitro groups, requires the application

of special methods. They may be divided into three groups.

1. Nitroso groups are introduced and subsequently they are oxidized to nitro
   groups. Since for each phenolic group one nitroso group can be introduced, the
   method may be applied for the preparation of nitro derivatives of polyhydric
   phenols in which the number of nitro groups is equal to the number of hydroxyl
   groups (e.g. dinitroresorcinol). The method is also applied when polyhydric
   phenols nitrate very easily (e.g. phloroglucinol), since their direct nitration proceeds
   too violently, and by breaking the process into two stages - nitrosation and oxi-
   dation of the nitroso groups - it can be made to run more smoothly.


2. A compound is nitrated which in addition to phenolic groups contains some
   other which inhibits the introduction of nitro groups and after the nitration becomes
   so mobile that it can readily be removed. A carboxylic group may serve the purpose.
   For example, by the nitration of resorcylic acid, dinitroresorcinol may be obtained
   as an end product (for more details see p. 537).


3. Halogenated phenols or polyhalogen derivatives of benzene are nitrated.
   After the compound has been nitrated, the halogen atom or atoms become reactive
   and may be removed by hydrolysis. This method, which is widely utilized in the
   preparation of dinitrophenol, has not found wider practical application because

of difficulties in obtaining supplies of the corresponding starting materials (some

halogen compound;).

Among all the possible nitro derivatives of resorcinol only di- and tri-nitroresorci-

nols are of practical value. Both are used as initiating explosives in the form

of lead salts (Vol. III). The lead salt (Pb

2+

) of dinitroresorcinol is also of some

practical value and in this connection some data characteristic of the compound

will be given.

DINlTRORESORCINOL

Two isomers of dinitroresorcinol, 2,4- (or 2,6-) and 4,6-dinitroresorcinols are

known (m. p. 148°C and 212.5°C respectively).