Density functional theory study of the mechanisms of oxidation of ethylene by chromyl chloride

Abstract

The mechanistic pathways for the formation of epoxide, 1,2-dichloroethane, 1,2-chlorohydrin, acetaldehyde, and vinylalcohol precursors in the oxidation of ethylene by chromyl chloride has been studied using hybrid density functionaltheory at the B3LYP/LACVP* level of theory. The formation of the epoxide precursor(Cl2(O)Cr-OC2H4)was found totake place via initial[2þ2]addition of ethylene across the CrdO bonds of CrO2Cl2to form a chromaoxetaneintermediate. The pathway involving initial[3þ2]addition of ethylene to the oxygen and chlorine atoms of CrO2Cl2,which has not been explored in earlier studies, was found to be favored over[3þ2]addition of olefin to two oxygenatoms of CrO2Cl2. The formation of the 1,2-dichloroethane precursor, which was found to take place via[3þ2]addition of ethylene to two chlorine atoms of CrO2Cl2, is slightly favored over the formation of the epoxide precursor.The 1,2-chlorohydrin precursor has been found to originate from[3þ2]addition of ethylene to the oxygen and chlorineatoms of CrO2Cl2as opposed to[2þ2]addition of ethylene to the Cr-Cl bond. The vinyl alcohol precursorOdCrCl2-(OH)CHdCH2has been found to exist only on the triplet potential energy surface. The acetaldehydeprecursor(OdCrCl2-OCHCH3)was found to be the most stable species on the reaction surface. Hydrolysis may berequired to generate the epoxide, 1,2-dichloroethane and 1,2-chlorohydrin from the respective precursors.