Process for the production of dianhydrohexitol mixtures and liquid mixture of dianhydrohexitols

摘要

Liquid dianhydrohexitol mixtures are prepared from diacylation products of hexitols and compounds such as organic carboxylic acids, carboxylic acid anhydrides, carboxylic acid halides, ketene and carbonic acid ester derivatives. More specifically, such diacylation products are simultaneously dehydrated and isomerized by subjecting them to a temperature of at least 130 C. in the presence of a strong acid to yield diacylated dianhydrohexitol isomer mixtures. These isomer mixtures are then converted to dianhydrohexitol isomer mixtures by hydrolysis or transesterification. Suitable strong acids include proton acids, Lewis acids and heterogeneous acid catalysts (e.g., ion exchange resins). The mixtures of the present invention are characterized by a minimal tendency towards crystallization. These mixtures are particularly useful as chain extending agents in the production of polyurethanes.