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540 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Wilkinson’s method has been studied by Aubertein and Emeury [29]. They

found that the yield of the product is reduced when the proportion of nitrite is

increased, and the rate of reaction is diminished. A relatively high proportion of

nitrite (2-4%) in the sulphonating acid considerably increases foaming during

nitration. The quantity of sodium nitrite should, therefore, be kept within the limits

of l-2%. A temperature of 50-55°C should be maintained at the beginning of

nitration. Increasing the temperature by 1.5°C reduced the yield by 1%.

The product thus obtained has a chestnut brown colour and m. p. 165-168.5°C

depending on the proportion of nitrite used.

Method of preparation

Trinitroresorcinol is usually prepared by a method which consists in the sulpho-

nation of resorcinol to disulphonic acid which is then nitrated. The process comprises

two stages: sulphonation and nitration.

Sulphonation yields only three compounds: I, II, and III.

I II III

The sulphonic acids I and II can be obtained by sulphonation of resorcinol with

sulphuric acid or oleum at temperatures which are not higher than 100°C (Mertz

and Zetter [32]). The trisulphonic acid can only be prepared by the action of oleum

at 200°C. According to Aubertein and Emeury [29], resorcinol can be sulphonated

to the compound II by the action of a tenfold quantity (by weight) of sulphuric

acid of concentration 92-97.5% H 2 SO 4 or oleum (105% H 2 SO 4 ) at 50°C. However,

a small proportion (1%) of resorcinol remains unchanged and is subjected to oxi-

dation during the subsequent nitration. It is responsible for foaming during the

nitration. According to the above authors, prolonged sulphonation or application

of more concentrated oleum does not prevent the presence of unsulphonated resor-
cinol.

Nitration can be achieved by acting with nitric acid (50-90% HNO 3 ) on sulph-

onated resorcinol partly dissolved and partly suspended in the excess of sulphuric

acid (Mertz and Zetter [32]), keeping the temperature below 55°C on mixing ihe

reagents and raising it to 80°C by the end of the reaction.

All who have carried out this reaction in practice know that during nitration
foaming occurs and sometimes makes the process impossible on a larger scale.

Strong foaming also means the formation of very fine crystals of styphnic acid

difficult to filter.