Process for the preparation of acid anhydrides

A process for the preparation of a symmetrical acid anhydride of formula ##STR9## wherein R.sub.1 is an aliphatic, cycloaliphatic, aromatic, cycloaliphatic-aliphatic or araliphatic radical, with the proviso that functional groups present in R.sub.1, if necessary, are in protected form,

• which process comprises reacting a compound of formula ##STR10## wherein R.sub.1 has the meanings assigned to it above, and wherein X is chloro or bromo, with an acid anhydride of formula ##STR11## wherein R.sub.2 is an aliphatic hydrocarbon radical or cycloalkyl, with removal by distillation of the compound of formula ##STR12## wherein R.sub.2 and X have the meanings assigned to them above, and removing any protective groups present.