TOLUENE, methyl benzene, CaiCH2, is an aromatic hydrocarbon present in American petroleum, in wood-tar and in coal-tar. Upon distillation coal-tar yields a fraction known as light oil, boiling at 100°-120° C. The toluene of commerce has been obtained from this frac tion. Toluene has also been prepared (1) by the dry distillation of tolu balsam; (2) by heating brombenzene with methyl iodide and metallic sodium (Fittig Synthesis) ; (3) by treating benzene with methyl halide and dry aluminum chloride (Friedel-Craft Synthesis); (4) by heating toluic acid with lime.
The enormous demand for toluene created by the European War, made it the subject of a number of patents. According to Fr. P. 479, 295, the compound is made by passing hydro chloric acid into boiling methyl alcohol in the presence of dehydrated zinc chloride and con ducting the methyl chloride produced into a mixture of benzene and dry aluminum chloride. Other patentees claim to have obtained toluene ' from gas-tar naphtha by distilling under press ure at 130°-240° C. (U. S. 1,225,237); or, from gas-drip naphtha, by passing it with steam and water-gas through checkerwork heated to about 800° C. (U. S. 1,230,087). To these may be added the widely-advertised °cracking)) process, according to which toluene and benzene have been obtained by heating oils, containing ali phatic or aromatic hydrocarbons, at prescribed temperatures and pressures. The process has been tried on a large scale, but its success as a commercial enterprise has been seriously ques tioned. Of much greater importance are the
improvements inaugurated for the extraction of the maximum amount of toluene from coke oven or city gas supplies. It has been known for some time that only a small fraction of the toluene obtained from the by-products coke ovens is recovered for commercial purposes. the greater proportion finding its way into city gas during the process of distillation. Toluene recovery plants have, therefore, been installed in all parts of the United States with the object of stripping illuminating gas of this material. As a result of this measure the toluene output for 1918 has probably exceeded 20,000,000 gal lons. The maximum output for 1912-13 was not over 500,000 gallons.
Toluene is a colorless liquid with a boiling point of 110° C. and a specific gravity of 0.872 at 15° C. It is an excellent solvent for many organic compounds. With a side-chain that readily responds to a number of reagents and with a nucleus that can be nitrated, sulphonated. halogenated or reduced, toluene is capable of forming a large number of derivatives which are either useful commercial products or in termediates for the manufacture of explosives, Synthetic dyes, perfumes, drugs, substitutes for sugar and poisons used in chemical warfare. Trinitrotoluene, saccharin, indigo-blue, brow benzyl cyanide, benzyl chloride, benzotrichloride, benzoic acid, nitrobenzaldehyde, toluidine, are some of the more important derivatives of this hydrocarbon.