NITROBENZENE, the simplest aromatic nitro-compound, was first isolated in 1834 by E. Mitscherlich, and is prepared commercially by the gradual addition of benzene to a well-cooled mixture of concentrated nitric and sulphuric acids, the oily product being separated, washed with alkali, and then distilled. It is a yellowish liquid possessing a strong smell of oil of bitter almonds. It boils at 209° C, and melts at 5.7° C. The products of its electrolytic reduction vary with the con ditions : in sulphuric acid solution it yields para-aminophenol (L. Gattermann, 1893) ; in alcoholic alkaline solution it yields azoxybenzene; in acid alcoholic solution, benzidine; in ammoniacal alcoholic solution, phenylhydrazine. With chlorine, in the presence of iodine or antimony chloride, it yields meta-chloronitrobenzene. It occasionally acts as an oxidizing agent, as in the preparation of quinoline and fuchsine (magenta, q.v.). It is used commercially for the preparation of aniline (q.v.) and of benzidine (q.v.) ; and in perfumery (oil of mirbane).
Dinitrobenzenes, C61-14(NO2) 2.—Ortho-dinitrobenzene, produced in small quantity in the preparation of meta-dinitrobenzene, forms colourless crystals which melt at 116.5° C and boil at 319° C (773
mm.). When boiled with aqueous caustic soda, it yields ortho nitrophenol. Meta-dinitrobenzene is formed by the direct nitration of nitrobenzene with fuming nitric acid, the product being poured into water and recrystallized from dilute alcohol. It forms prac tically colourless needles which melt at 89.7° C, and boil at 3.02.8° C. It is used for the preparation of meta-phenylenediamine. Para-dini trobenzene results from the action of nitrogen peroxide on an ethereal solution of quinone dioxime ; it crystallizes in colourless needles, which melt at 170-172° C.
Trinitro benzenes, C61-13 ( NO2) 3.—Asymmetrical (I: 2 : 4) trinitro benzene results from the action of fuming nitric and sulphuric acids on It forms yellow crystals, which melt at 57.5° C. When boiled with dilute aqueous caustic soda it yields 2 : 4-dinitrophenol. Symmetrical (1:3:5) trinitrobenzene is formed by the further nitration of meta-dinitrobenzene with fuming sulphuric and nitric acids; or by the action of water on 2:4:6-trinitrobenzoic acid (German patent 77,353). It crystallizes in prisms which melt at 12i° C.