A process is described for the acid-catalyzed dehydration of a sugar alcohol, wherein the catalyst comprises a water-tolerant Lewis acid. In particular embodiments, the catalyst comprises a homogeneous water-tolerant Lewis acid, especially a homogeneous Lewis acid selected from the group consisting of bismuth (III) triflate, gallium (III) triflate, scandium (III) triflate, aluminum triflate, tin (II) triflate and indium (III) triflate. Such catalysts are effective for dehydrating both of sorbitol and the 1,4-sorbitan dehydration precursor of isosorbide, and bismuth (III) triflate particularly is beneficial for dehydrating mannitol to isomannide.
