urbaf2

MANUFACTURE OF PICRIC ACID

may be removed from time to time through door (3). Crystals of the required

size pass through the gauze into hopper (4).

FIG. 121. Chamber drier for picric acid (Lebedev [5]).

The sieve is hung on straps from the ceiling and is kept in oscillating motion

by means of an eccentric driven from a compartment adjacent to that in which the

screening installation is located. The end product is transported in leakproof chests

or in paper-lined barrels.

FIG. 122. Sieve for picric acid (Pascal [2]).

DINITROPHENOL NITRATION METHODS

The nitration of dinitrophenol is the most modern commercial method for the

production of picric acid from chlorobenzene via chlorodinitrobenzene (for prep-

aration of dinitrophenol from chlorodinitrobenzene, see p. 484).

Both dry and moist dinitrophenol may be nitrated, though the dry product

is usually used.

Lebedev [5] describes the production process used in the U.S.S.R. Dinitro-

phenol from the centrifuge, containing 10-15% of moisture, is dried to obtain a prod-

uct with only about 0.5% of moisture (drying is effected in picric acid driers).

Since the purity of picric acid depends to a high degree on the purity of the

dinitrophenol, the quality standards for the latter should be strictly observed (see

p. 486).