A novel production of γ-butyrolactone catalyzed by cationic hydridoruthenium complexes

Abstract

γ-Butyrolactone (GBL) is produced by a two-stage hydrogenation of maleic anhydride (MAH) in the liquid phase: a hydrogenation of MAH to succinic anhydride (SAH) in the first stage and a hydrogenation of SAH to GBL in the second stage. A novel ruthenium catalyst system consisting of Ru salts, trialkylphosphine and p-toluenesulfonic acid was found very effective for the hydrogenation of SAH affording GBL in selectivities above 96%. Acid promoters like p-toluenesulfonic acid induce structual change in the ruthenium complexes, leading to the cationic complexes, which show higher catalytic activity and selectivity than the neutral complexes. A process to maximize the performance and stability of the catalyst to produce GBL was developed. Novel features of this process are the external preparation of the Ru complexes, the reaction protocol which combines over-flow reaction with stripping for the constant removal of H2O, and the catalyst recovery system by the extraction.