Process for the aftertreatment of betaines and amphoteric surfactants

A process for reducing the content of dichloroacetic acid in a water-containing paste or solution of a betaine surfactant containing dichloroacetic acid residues wherein the betaine surfactant is at least one compound of the formula I or II ##STR3## in which R.sup.1 is an alkyl or alkenyl radical containing from 6 to about 22 carbon atoms, and R.sup.2 and R.sup.3 independently of one another represent an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, ##STR4## in which R.sup.4 CO is a saturated or unsaturated acyl radical containing 6 to 22 carbon atoms, R.sup.5 is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, R.sup.5 is an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, and n=2 or 3, comprising the steps of

• A) adding an alkali metal hydroxide to said paste or solution until a pH in the range of from about 11 to about 14 is obtained;
• and
• B) thermally treating the resulting mixture until a significant reduction in residual dichloroacetic acid is achieved.