C6H6NO2

NITROBENZENE  , the simplest aromatic nitro compound . It was first isolated in 1834 by E . Mitscherlich (Pogg . Ann., 1834, 31, p . 625), 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 also results in the oxidation of aniline by monopersulphuric acid (H . Caro, Zeit. angew . Chem., 1898, p . 845) or by potassium permanganate (E . Bamberger, Ber., 1893 . 26, p . 496); by the oxidation of nitrosobenzene (below) with atmospheric oxygen; or by the decomposition of benzene diazonium nitrate mercury nitrite, Hg(NO2)2.2C6H,N2•NO3, with copper powder (A .

Hantzsch, Ber., 1900, 33, p . 2551) . It is a yellowish liquid possessing a strong

smell of oil of bitter almonds . It boils at 209°C., and melts at 3.6° C . (C.E . Linebarger, Amer . Chem . Jour., 1896, 18, p . 437) . The products of its electrolytic reduction vary with the conditions: in sulphuric acid solution it yields para-aminophenol (L . Gattermann, Ber., 1893, 26, p . 1844); 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-chlornitrobenzene . Hydrobromic acid at 185°-19o°C. converts it into di- and tri-bromaniline . It occasionally acts as an oxidizing agent, as in the,'preparation of quinoline and fuchsine . It is used commercially for the preparation of aniline and of benzidine; and in perfumery (oil of mirbane) . Dinitrobenzenes, C6H4(NO2)2•—Ortho-dinitrobenzene is formed in small quantity in the preparation of meta-dinitrobenzene, and also results from the action of nitro-sulphuric acid on bismuth triphenyl (A . Gillmeister, Ber., 1897, 30, p . 2844) . It forms colourless crystals which melt at 116.5° C. and boil at 319° C . (773 mm.) . On boiling 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 re-crystallized from dilute alcohol . It forms practically colourless needles which melt at 89.7° C., and boil at 3o2.8° C .

It is used for the preparation of meta-phenylene diamine . Para-dinitrobenzene results from the action of

nitrogen peroxide on an ethereal solution of quinone dioxime (R . Oliveri-Tortorici, Gazz., 1900, 30, i.533) . It crystallizes in colourless needles, which melt at 170-1720 C . It is only slightly soluble in cold water and cold alcohol . Trinitrobenzenes, C6H3(NO2),.—Asymmetrical (1.2.4) trinitrobenzene results from the action of fuming nitric and sulphuric acids on para-dinitrobenzene . 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; by the action of hydrochloric acid on sodium malonyl aldehyde (H . B . Hill and J . Torray, Ber., 1895, 28, 2598), or by the action of water on 2.4.6-trinitrobenzoic acid (German patent 77353) .

It crystallizes in prisms which melt at 121° C . It yields addition compounds with aniline and

naphthalene, and combines directly with potassium methylate, sodio-malonic ester and hydrocyanic ester . Alkaline potassium ferricyanide oxidizes it to picric acid . Nitrosobenzene, C6H5NO, was first obtained by the action of nitrosyl bromide or chloride on mercury diphenyl (A . Baeyer, Ber., 1874, 7, p . 1638) . It results, with other products, in the oxidation of phenyl diazonium chloride with alkaline potassium ferricyanide; of $-phenylhydroxylamine with chromic acid mixture (E . Bamberger, Ber., 1893, 26, pp . 473, 483, 1894, 27, p . 1349), or of aniline by monopersulphurlc acid (German patent 110575) . It exists in two crystalline forms . Nitric acid passed into its chloroform solution gives phenyl diazonium nitrate .

With aniline and acetic acid it yields azobenzene . It combines with aromatic

amines to form azocompounds, with arylhydroxylamines to form azoxy compounds, and with hydroxylamine it gives isodiazobenzene .