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Theoretically toluene should yield three isomeric monosulphonic acids, in which the entering sulphonic acid group occupiesthe positions ortho, meta, or para to the methyl group.
The action of sulphuric acid on toluene was first investigatedby Jaworsky, (Ztschr. Chem. 1,272), who described onetoluene sulphonic acid as the resulting compound. In 1869 Engelhardtand Latschinoff (Ibid. 617), heated toluene with sulphuricacid and made and studied the potassium salt of the resulting acid.They obtained two forms, and identified them by fusion with causticpotash which converted them into the ortho and para cresols,showing that sulphonation had taken place in the positions orthoand para to the methyl group.
Barth (Ann. chem. (Liebig) 152,91), working similarlybut fusing under different conditions which also caused oxidationof the methyl group to a carboxyl group obtained para hydroxybenzoic acid and salicylic acid (ortho hydroxy benzoic acid.) Thisalso proved that the sulphonic acid group had entered in the orthoand para positions.
Anna Wolkow (Ztschr. Chem (1870) 321), confirmed thiswork but ascribed the meta position to the sulphonic acid thatpassed into salicylic acid. She also made two acid chloridesand amides and recorded their melting points.
Fittig and Ramsay (Ann. chem. (Liebig) 168,242) studiedthis result of Anna Wolkow, and to determine and settle the constitutionsof the sulphonic acids, carefully prepared and purified2their sulphonic acids; they proved definitely that no meta acidwas formed, and that the products were only the ortho and par