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570 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Hcxanitrodiphenylurea (hexanitrocarbanilide, sym-dipicrylurea) forms pale

yellow crystals melting at 208-209°C (with decomposition). It was obtained by

Perkin [36] and Reudler [37]. Davis [38] was the first to suggest its use as an explo-

sive. The compound is prepared by the nitration of sym-diphenylurea, which may

be obtained by reacting phosgene with aniline, or more simply, by heating aniline

with urea at 160-165°C. Davis proposed the nitration of diphenylurea in two

stages: first tetranitrodiphenylurea is obtained, and this in turn is nitrated to hexa-

nitrodiphenylurea.

When heated with dilute sulphuric acid, hexanitrodiphenylurea is hydrolysed,

forming picric acid. With ammonia it produces a deep red colour, which is ascribed

to the formation of an ammonium salt of the aci-form. Boiling with aqueous ammo-

nia solution causes hydrolysis with the formation of picramide.

The compound has a high initiation temperature (345°C). However, because

of its susceptibility to hydrolysis its chemical stability is too low for it to be used

as an explosive, although its explosive power is somewhat higher than that of TNT.

Its sensitivity to impact is similar to that of tetryl.

HEXANITRO-OXANILIDE

The use of hexanitro-oxanilide (m. p. 295-300°C) as an explosive material was

suggested by the Societe Anonyme d’Explosifs [39].

The compound is prepared by the direct nitration of oxanilide (Mixter and

Walther [40]). Domanski and Mieszkis [41] investigated the explosive properties

of hexanitro-oxanilide and found the following values for the rate of detonation

of the pressed product mixed with 2% of dinitrotoluene:

at a density of 0.90 g/cm^3 5100 m/sec

,, ,, ,, ,, 1.20 ,, 5500 ,,

,, ,, ,, ,, 1.47 ,, 6800 ,,

It follows from the above that the explosive power of the compound is similar
to that of TNT. The fact that it readily undergoes hydrolysis, forming picric acid

and oxamide is a serious drawback and prevents its use as au explosive.