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). XXIV 1,3,5-TRINITROBENZENE C6H2(NO2)3CO2H--> C6H3(NO2)3 + CO2 Prepared by H. T. CLARKE and W. W. HARTMAN. Checked by J. B. CONANT and J. J. TOOHY. 1. Procedure THE crude trinitrobenzoic acid obtained by oxidation of 360 g. of trinitrotoluene (prep. XXV, p. 95) is mixed with 2 l. of water at 35'0 in a 5-l. flask provided with a stirrer. Fifteen per cent sodium hydroxide solution is added, with continuous stirring, until a FAINT red color is just produced. (See Notes.) The color is then immediately discharged by means of one or two drops of acetic acid, and the liquid is filtered from unchanged trinibrotoluene. The filtrate is transferred to a 5-l. flask, and 70 cc. of glacial acetic acid are added. The mixture is then gently heated, with continuous stirring, when trinitrobenzene separates in crystalline condition, and floats on the surface of the liquid as a frothy layer. After about one and a half hours the evolution of gas ceases; at this point the crystals begin to stir into the solution. The heating and stirring is continued for three-quarters of an hour, when the mixture is allowed to cool, and the crystals filtered off. A sample of the filtrate should be tested for undecomposed trinitrobenzoic acid: if a precipitate is produced by the addition of sulfuric acid the process must be continued. After recrystallization from glacial acetic acid, the product melts at 121-122'0. The yield is 145-155 g. (43 to 46 per cent of the theoretical amount calculated from the trinitrotoluene). 2. Notes