ABSTRACT
Abstract 2,5-Dihydrofuran (2,5-DHF) is typically produced by the catalytic rearrangement of 3,4-epoxy-1-butene (1) using an inorganic Lewis acid and inorganic or onium iodide in a polar, aprotic solvent. For years, commercial processes utilizing this chemistry were unattractive due to the high cost of 1 and side reactions in the rearrangement step. Recovery of the expensive catalysts and solvent was difficult and presented a serious problem for scale-up. Following the discovery of an economical process for 1, the production of 2,5-DHF was once again of industrial interest. This paper describes the development of a continuous, liquid phase process utilizing a trialkyltin iodide and tetraalkylphosphonium iodide co-catalyst system which gives high selectivity for 2,5-DHF and provides an efficient means for catalyst recovery. Introduction 3,4-Epoxy-1-butene (1) is a versatile intermediate for the production of commodity, specialty and fine chemicals (2). An important derivative of 1 is 2,5-dihydrofuran (2,5-DHF). This heterocycle is useful in the production of tetrahydrofuran (3), 2,3dihydrofuran (4), 1,4-butanediol (5), and many fine chemicals (e.g., 3formyltetrahydrofuran (6) and cyclopropanes (7)). The homogeneous, Lewis acid and iodide salt-catalyzed rearrangement (isomerization) of 1 to 2,5-DHF has been known since 1976 (8) and is the only practical method for 2,5-DHF synthesis.
