Process for the preparation of 4-nitrotoluene-2-sulphonic acid

摘要

In the known processes, an explosive decomposition of the reaction mixture can occur due to exceeding of the temperature during the reaction. Processes in which sulphur dioxide is used as a solvent additionally require an increased outlay in terms of apparatus. The novel process is intended to be environmentally compatible and safe to control, and to afford high yields. The novel process consists in alternately adding dropwise p-nitrotoluene dissolved in dichloroethane and, per mole of p-nitrotoluene, 1.6 mol of sulphur trioxide in portions into dichloroethane initially introduced as a solvent, raising the temperature to 75 DEG C to 80 DEG C, after about 45 minutes adding 0.4 mol of sulphur trioxide per mole of p-nitrotoluene, stirring at the abovementioned temperature for about 75 minutes and working up the reaction solution. The process is used for the preparation of 4-nitrotoluene- 2-sulphonic acid, which is employed e.g. as a starting material for the production of 4,4'-diaminostilbene-2,2'-disulphonic acid and of 4-aminotoluene-2-sulphonic acid, which are important in the preparation of dyestuffs.