Density Functional Theory Study of the Mechanisms of Oxidation of Ethylene by Chromyl Chloride

The mechanistic pathways for the formation of epoxide, 1,2-dichloroethane, 1,2-chlorohydrin, acetaldehyde, and vinyl alcohol precursors in the oxidation of ethylene by chromyl chloride has been studied using hybrid density functional theory at the B3LYP/LACVP* level of theory, The formation of the epoxide precursor (Cl(2)(O)Cr-OC(2)H(4)) was found to take place via initial [2 + 2] addition of ethylene across the Cr=O bonds of CrO(2)Cl(2) to form a chromaoxetane intermediate. The pathway involving initial [3 + 2] addition of ethylene to the oxygen and chlorine atoms of CrO(2)Cl(2), which has not been explored in earlier studies, was found to be favored over [3 + 2] addition of olefin to two oxygen atoms of CrO(2)Cl(2), The formation of the 1,2-dichloroethane precursor, which was found to take place via [3 + 2] addition of ethylene to two chlorine atoms of CrO(2)Cl(2), is slightly favored over the formation of the epoxide precursor. The 1,2-chlorohydrin precursor has been found to originate from [3 + 2] addition of ethylene to the oxygen and chlorine atoms of CrO(2)Cl(2) as opposed to [2 + 2] addition of ethylene to the Cr-Cl bond. The vinyl alcohol precursor O=CrCl(2)-(OH)CH=CH(2) has been found to exist only on the triplet potential energy surface. The acetaldehyde precursor (O=CrCl(2)-OCHCH(3)) was found to be the most stable species on the reaction surface. Hydrolysis may be required to generate the epoxide, 1,2-dichloroethane and 1,2-chlorohydrin from the respective precursors.