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484 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Since liquid impurities may produce exudates in explosive compositions, to

avoid this the crude product should be purified. For a preliminary washing, a dilute

(2%) solution of sodium carbonate may be used. Picric acid reacts with the

carbonate which then goes into solutions as sodium picrate. Instead of sodium

carbonate milk of lime or calcium hydrogen carbonate may be used.

Desvergnes describes the purification process used in various plants as follows.

A wooden double-bottomed vat of 650 1. capacity is charged with 350 kg of dinitro-

phenol, which is stirred with 200 1. of a 3% solution of calcium hydrogen

carbonate at a temperature of 70°C. The contents of the vat are allowed to remain

at rest for 1 hr, then the aqueous solution is decanted and the operation is repeated

with a fresh solution of calcium hydrogen carbonate. Then the purified product

is washed with cold water. The melting point of dinitrophenol obtained is about

105.5%

A product of still higher purity may be prepared by washing with sulphuric acid.

100 parts of dinitrophenol and 120 parts of sulphuric acid (sp. gr. 1.84) are agitated

for 12 hr at room temperature. Then the sulphuric acid is filtered off and the dinitro-

phenol is washed with a small quantity of fresh sulphuric acid and finally several

times with water. In this way the melting point of the product can be raised to

108.5°C.

The compounds dissolved both in the spent calcium hydrogen carbonate solu-

tions and in the sulphuric acid, such as mononitrophenols, dinitrophenols and picric

acid, may be recovered by precipitation: from the calcium hydrogen carbonate

solution by acidification, and from sulphuric acid solution by dilution with water.

The product thus obtained may be blended with dinitrophenol for the preparation

of picric acid.

MANUFACTURE OF DINITROPHENOL BY CHLORODINITROBENZENE

HYDROLYSIS

In industrial practice, hydrolysis of chlorodinitrobenzene is now the main

method of producing dinitrophenol. The reaction proceeds as follows:

(5)

From the resulting dinitrophenate, dinitrophenol is obtained by acidification.

Russian method

The following method (after Lebedev [39]) was applied in Russia (1915-1916)

and later in the U.S.S.R.