The Chemistry of Powder and Explosives - Sciencemadness Dot Org

162 AROMATIC NITRO COMPOUNDS
with water, in the proportion of 15 grams to the liter, filtering hot, and
allowing to cool slowly. The heavy droplets of brown oil which dissolve
only slowly during this boiling ought to be discarded. Pure picric acid
crystallizes from water in pale yellow flat needles, m.p. 122.5°. It may
be obtained in crystals which are almost white by recrystallizing from
aqueous hydrochloric acid.
The best process for the production of dinitrophenol is probably
the autoclaving of dinitrochlorobenzene with aqueous caustic
soda. The product is obtained on acidification and is used as
such, or is nitrated to picric, acid for the commercial production
of that material by the so-called synthetic process.
The "catalytic process" for the production of picric acid directly
from benzene in one step by the action of nitric acid in the
presence of mercuric nitrate has much theoretical interest and
has been applied, though not extensively, in plant-scale manufacture.
It yields about as much picric acid as is procurable from the
same- weight of benzene by the roundabout method of sulfonating
the benzene, converting the benzene sulfonic acid into phenol,
and nitrating the phenol to picric acid—and the benzene which is
not converted to picric acid is for the most part recovered as such
or as nitrobenzene. The first mention of the process appears to be
in the patent of Wolffenstein and Boeters. 55
Preparation of Picric Acid (Catalytic Process). Two hundred grams
of benzene in a 2-liter round-bottom flasK equipped with a sealed-on
condenser is refluxed on the sand bath for 7 hours with 600 cc. of nitric
acid (d. 1.42) in which 10 grams of mercuric nitrate has been dissolved.
The material is then transferred to another flask and distilled with
steam. Benzene comes over, then nitrobenzene, then finally and slowly
a mixture of dinitrobenzene and dinitrophenol. The distillation is continued
until all volatile matter has been removed. The liquid in the
flask is filtered hot and allowed to crystallize. If the picric acid is not
sufficiently pure, it is recrystallized from hot water.
Mercuric nitrate combines with benzene to form a deep-brown
or black addition compound, the probable structure of which is
indicated below. This material when warmed with nitric acid is
oxidized with the production of red fumes and the formation of
55 Wolffenstein and Boeters, Ger. Pat. 194,883 (1908); Ger. Pat. 214,045
(1909); Ramy, Brit. Pat. 125,461 (1918); MacDonald and Calvert, Brit.
Pats. 126,062, 126,084. 126,675, 126,676 (1918); Brewster. Brit. Pat. 131,403
(1919).