Sulphuric acid-catalysed formation of hemiacetal from glyoxal and ethanol

Abstract We examine the reaction of ethanol with glyoxal to form hemiacetal by means of the high-level G4(MP2) procedure. In this reaction, an intermolecular proton transfer is coupled with the formation of a covalent C O bond between the two molecules. We find a novel catalytic reaction mechanism in which an H 2 SO 4 catalyst reduces the barrier height from ∆ H ‡ 298  = 140.2 to 16.3 kJ mol −1 . It is well established that H 2 SO 4 can effectively catalyse intramolecular proton transfers. This letter shows that H 2 SO 4 can catalyse an intermolecular proton transfer that is coupled with a covalent bond formation.