The Chemistry of Powder and Explosives - Sciencemadness Dot Org

180 AROMATIC NITRO COMPOUNDS
If the benzene-insoluble material from crude tetryl is dissolved
in hot fuming nitric acid and allowed to cool, glistening
yellow crystals are procured. These, recrystallized from nitric
acid and then from acetone with the addition of two volumes of
ligroin, yield cream-colored small crystals of the third of the
above-indicated substances, 3,3',5,5'-tetranitro-4,4'-di- (methylnitramino)
-biphenyl, or 3,3',5,5'-tetranitrodimethylbenzidinedinitramine.
The material decomposes with foaming at 229-230° if
its temperature is raised at the rate of 6° per minute. If it is
heated more slowly, at 2° per minute, it melts partially and
decomposes at 222° with preliminary softening and darkening.
Like tetryl and other nitroamines, it gives a blue color with the
diphenylamine reagent. Although Willstatter and Kalk 92 have
found that monomethylaniline is not convertible into a benzidine
derivative by Michler's method, it is nevertheless true that the
benzene-insoluble by-products are produced during the preparation
of tetryl from monomethylaniline, as indeed Mertens first
procured them by the action of nitric acid on that substance.
The usual process for the preparation of tetryl from dimethylaniline
has the disadvantage that the by-products, namely, the
rw-nitrotetryl and the benzene-insoluble material, necessitate a
rather elaborate purification, and it has the further disadvantage
that one of the methyl groups of the dimethylaniline is destroyed
by oxidation (expense) with the production of red fumes (nuisance)
and the consequent loss of valuable combined nitrogen.
All these disadvantages find their origin at points in the reaction
earlier than the formation of dinitromonomethylaniline. 2,4-
Dinitromonomethylaniline, orange-yellow crystals, m.p. 174°,
nitrates smoothly to form tetryl without the production of
by-products or red fumes. Synthetic methyl alcohol is now available
cheaply and in a quantity which is limited only by the will
of the manufacturers to produce it. It reacts with ammonia (from
the fixation of nitrogen) at elevated temperatures in the presence
of a thorium oxide catalyst to form methylamine, 93 and methylamine
reacts with dinitrochlorobenzene to form dinitromonomethylaniline.
There seems every reason to believe that tetryl in
the future will be manufactured chiefly, or wholly, from dinitrochlorobenzene.
m Ber., 37, 3771 (1904).
93 Davis and Elderfield, J. Am. Chem. Soc, 50, 1786 (1928).