Toluenesulfinic acid and its salts have been prepared by three
general methods: (1) The reduction of the sulfonyl chloride.
The reagents which have been used for this are sodium amalgam,[1] zinc
dust in alcohol or water,[2] sodium sulfite,[3] sodium sulfide,[4]
potassium hydrosulfide[5] (the thio acid being first formed)
and sodium arsenite.[6] (2) From toluene by the Friedel and
Crafts reaction, using either sulfur dioxide and hydrogen chloride[7]
or sulfuryl chloride.[8] (3) From _p_-toluidine by diazotization
and subsequent treatment with sulfur dioxide and finely divided
copper.[1b] The compound has also been obtained in certain
reactions which, however, would not be suitable for preparative work;
thus it is formed by hydrolysis and reduction of certain thio
derivatives[2b] prepared from the acid itself and also by the
decomposition of ditolylsulfonmethylamine.[3b]
[1] Ann. 142, 93 (1867).
[2] Ber. 9, 1586 (1876).
[3] Ber. 3, 965 (1870).
[4] D. R. P. 224,019; Chem. Zentr. 1910, (II), 513.
[5] Ber. 42, 3821 (1909).
[6] Ber. 41, 3351 (1908); Ber. 42, 480 (1909).
[7] Ber. 41, 3318 (1908); J. Chem. Soc. 93, 754 (1908).
[8] Rec. trav. chim. (2) 30, 381 (1911).
[1b] Ber. 32, 1141 (1899); J. Chem. Soc. 95, 344 (1909).
[2b] Ber. 15, 130 (1882); 20, 2088 (1887); 41, 3351 (1908).
[3b] J. prakt. Chem. (2) 63, 170 (1901).