Process for the preparation of sulfonic acid chlorides

In a process for the preparation of a sulfonic acid chloride of the formula ##STR8## wherein R.sup.1, R.sup.2 and R.sup.3 are identical or different and denote hydrogen, a lower alkyl or cycloalkyl radical, halogen, aryl, aralkyl, aryl-ether or one of the radicals ##STR9## or where adjacent radicals R.sup.1 and R.sup.2 are linked to form a cycloaliphatic or aromatic carbocyclic ring which is optionally substituted by a sulfonic acid chloride group

• by contacting an aromatic compound of the formula ##STR10## wherein R.sup.1, R.sup.2 and R.sup.3 have the previously assigned significance
• with a sulfonating agent in the presence of thionyl chloride, the improvement which comprises employing an approximately equimolar amount of said sulfonating agent, based upon the number of sulfonic acid chloride groups to be introduced, employing an excess of thionyl chloride, the sulfonating agent and thionyl chloride being initially introduced or added simultaneously with the addition of said aromatic compound, said process further characterized in that:
• A. the sulfonating agent and the thionyl chloride are initially introduced and the aromatic compound is added thereafter;
• or
• B. the sulfonating agent is initially introduced into a reaction zone and the aromatic compound and thionyl chloride are simultaneously added thereto thereafter;
• the process being carried out at a temperature in the range of 20.degree. to 90.degree. C.