Process for the preparation and purification of thermolabile compounds

A process for the preparation of a glycolide of the general formula ##STR2## wherein R.sub.1 and R.sub.2 independently of one another are hydrogen or a branched or unbranched alkyl radical with up to 16 carbon atoms, from the corresponding low molecular weight poly-.alpha.-hydroxycarboxylic acid or an .alpha.-halogenocarboxylic acid salt in the presence of a catalyst, wherein the starting compound is subjected to thermolysis which is carried out continuously under forced conveyance in a reactor with a rising temperature gradient, and the glycolide formed is distilled off.