Preparation of 1,2-benzisothiazolones

In a process for preparing 1,2-benzisothiazolones and their alkali metal salts by reacting 2,2'-dithiodibenzamides in an aqueous alkaline solution, the improvement which comprises reacting 2,2'-dithiodibenzamides of the formula ##STR4## in which R.sup.1 and R.sup.2 are identical or different and are each hydrogen, halogen, alkyl, haloalkyl or alkoxy of 1 to 6 carbon atoms, aryl or aralkoxy and aralkyl or alkylaryl of up to 12 carbon atoms, or in which R.sup.1 and R.sup.2 together form an aliphatic or aromatic ring and in which R.sup.3 is hydrogen, alkyl of 1 to 6 carbon atoms or aryl or alkylaryl of 6 to 10 carbon atoms, in the presence of oxygen supplied to the reaction mixture in an amount of 1.0 to 10.0 moles per mole of the compound I while ensuring thorough mixing of the reaction mixture with oxygen during the reaction.