XI.—Dinitro-benzol.
§ 247. Dinitro-benzol, C6H4(NO2)2 (ortho-, meta-, para-).—The ortho-compound is produced by the action of nitric acid on benzol, aided by heat in the absence of strong sulphuric acid to fix water. Some of the para-dinitro-benzol is at the same time produced. The meta-compound is obtained by the action of fuming nitric acid on nitro-benzol at a boiling temperature.
The physical properties of the three dinitro-benzols are briefly as follows:—
Ortho-d. is in the form of needles; m.p. 118°.
Meta-d. crystallises in plates; m.p. 90°.
Para-d. crystallises, like the ortho-compound, in needles, but the melting-point is much higher, 171° to 172°.
Just as nitro-benzol by reduction yields aniline, so do the nitro-benzols on reduction yield ortho-, meta-, or para-phenylene diamines.
Meta-phenylene diamine is an excellent test for nitrites; and, since the commercial varieties of dinitro-benzol either consist mainly or in part of meta-dinitro-benzol, the toxicological detection is fairly simple, and is based upon the conversion of the dinitro-benzol into meta-phenylene-diamine.
Dinitro-benzol is at present largely employed in the manufacture of explosives, such as roburite, sicherheit, and others. It has produced much illness among the workpeople in the manufactures, and amongst miners whose duty it has been to handle such explosives.