Process for the preparation of a compound with at least one five-membered cyclic monothiocarbonate group wherein a) a compound with at least one epoxy group is used as starting material b) the compound is reacted with phosgene or an alkyl chloroformate thus giving an adduct and c) the adduct is reacted with a compound comprising anionic sulfurthus obtaining the compound with at least one five-membered cyclic monothiocarbonate group.