N1TRO-BENZOLS ; NITRO-TOLUOLS ; NITRO-XYLOLS.—Benzol, toluol, and xylol dissolve in nitric acid, with evolution of heat ; on the addition of water, the nitro-compounds are obtained, as heavy oily liquids.
By boiling benzol with strong nitric acid, or with a mixture of strong sulphuric and nitric acids, dinitro-benzol is forrned. Toluol forms two isomerides with nitric acid, Which are separated by distillation : 1.4 nitro-toluol melts at 54° (129° F.), and boils at 237° (459° F.); 1.2 nitro toluol does not solidify in a freezing mixture, and boils at 223° (433° F.). Dinitro-toluol exists in two forms : the first is produced by acting on 1.1 or • 2 nitro-toluol, with hot concentrated nitrie acid, and crystallizes from alcohol in long, colourless, brittle needles, melting at 71° (160° F.); the second is obtained from 1.3 nitro-toluol, with concentrated nitric acid, and forms long, yellow needles, melting at 60° (140° F.). Xylol, or iso-xylol forms similar compounds : nitro-isoxylol is a pale. yellow liquid, boiling at 239° (462° F.); the dinitro compound crystallizes front alcohol in long, brilliant prisms, melting at 93° (199° F.) ; the trinitro forms colourless crystals, melting at 177° (351° F.). Before nitrating toluol and xylol, it is important to wash out all traces of the heavy oils, in the same way as from naphtha and benzol (q. v.), otherwise explosive compounds may be formed.
Nitro-benzol was first made on the large scale by Collas, at Paris, and was sold under the narne of " Essence of Mirbane." It is generally prepared by the action of two parts fuming nitric acid and one part concentrated sulphuric acid ; the benzol is placed in the still, and the acids are gradually added, with agitation ; the nitric acid must be applied slowly, until red fumes appear. The end of the reaction is indicated by the liquid becoming colourless, or nearly so, and separating into two distinct strata, on the addition of water.
Figs. 484 and 485 represent one of a series of apparatus described by Perkins (Cantor Lectures) as being used for its manufacture in this country : a, cast-iron pot stancling on brickwork ; b, outlet for finished product ; 0, inlet for raw materials ; d, an iron pipe to carry away nitrous fumes, connected with a condenser for collecting the benzol which is evaporated ; e, spindles of stirrers, worked by toothed gearing, and entering the pot through a water-lute supplied with nitro-benzol ; the pots are cooled by water flowing over them, as at f. The use of
the sulphuric aoid is to take" up the water which is formed, thus keeping the nitric acid undilute, and preventing acdon on the pot.
When b is opened, a mixture of acids first runs out ; then the nitro-benzol, which is washed and distilled, if necessary. Washing may be effected in closed cast-iron tanks, sup plied with exhausters, for drawing off the nitrous fumes, and, at the bottom, with a per forated serpentine ooil for conveying lime water, or water, in the form of fine spray. The final washing is made with water, but the presence of a little lime is not detrimental. Distillation should be performed by steam.
Nitro-benzol has generally a brown colour, but when quite pure, is a pale-yellow, strongly refractive liquid, boiling at 220° (428° F.) ; it has a burning sweet taste, and 21 smell resetubling that of oil of bitter almonds and cinnamon ; its spe,cific gravity is about 1.200.
Nitrate of soda is sometimes used instead of nitric acid ; in this case, the sulphuric acid added must be sufficient to convert the soda into the acid sulphate. The advantage is the comparative inexpensive production of concentrated nitric acid. The same apparatus is applicable.
When properly made, the yield of nitro-benzol should be 130-135 per cent. on the benzol employed. Three kinds are met with in commerce :—" Light," boiling between 204° and 210° (400° and 410° F.), constituting the " essence of mirbane,'' and used for scenting common soaps, and in low-elssa perfumery ; " heavy,'' boiling between 210° and 220° (410° and 428° F.), poszessing a fatty smell and rather dark colour, used chiefly for the preparation of aniline reds ; " very heavy,' boiling between 221° and 235° (430° and 455° F.), with disagreeable smell, and chiefly used for colours requiring high-boiling anilines, The essence of mirbaue is sold as artificial oil of bitter almonds.