The crude trinitrobenzoic acid obtained by oxidation of 360 g. (1.6 moles) of trinitrotoluene (p. 543) is mixed with 2 l. of water at 35° (Note 1) 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 (Note 2). The color is then immediately discharged by means of one or two drops of acetic acid, and the liquid is filtered from unchanged trinitrotoluene. The filtrate is transferred to a 5-l. flask, and 70 cc. of glacial acetic acid is added.

The mixture is then gently heated (Note 3), 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 one-half hours the evolution of gas ceases; at this point the crystals begin to stir into the solution. The heating and stirring are 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°. The yield is 145–155 g. (43–46 per cent of the theoretical amount calculated from the trinitrotoluene).