Quantum chemical study of the mechanisms of oxidation of ethyleneby Molybdyl and Tungstyl Chloride

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Indian Academy of Sciences.
The mechanisms of oxidation of olefins with MoO2Cl2and WO2Cl2are studied with DFT. Theformation of epoxide from these reactions is not very feasible by any of the postulated paths. If the epox-ide precursor will form at all, it will ariseviainitial [3+2]O,Claddition of ethene to MoO2Cl2and WO2Cl2to form an intermediate, followed by re-arrangement to form the precursor, from which the epoxide can begenerated by hydrolysis. The chlorohydrin precursor was also found to originate from [3+2]O,Claddition ofethene to MO2Cl2. The results also indicate that a dichloride is not a likely product in the oxidation of ethyleneby molybdyl chloride. However, in the case of WO2Cl2, the formation of a dichloride may not be precluded.The formation of acetaldehyde and vinyl alcohol from the oxidation of ethylene does not appear energeti-cally feasible with MoO2Cl2, but appears thermodynamically plausible with WO2Cl2. Thus, the oxidation ofethylene with MoO2Cl2will most likely lead to the formation of chlorohydrins predominantly via [3+2]O,Claddition; oxidation with WO2Cl2may also form chlorohydrins, but only extremely slowly. The oxyhalidesMO2Cl2become weaker oxidants in the order CrO2Cl2>>MoO2Cl2>WO2Cl2. Corresponding to this, reac-tions involving reduction of the metal [3+2] and [2+1] show a sharp increase in barrier going from Cr to W;reactions without a change in metal oxidation state ([2+2]) show much smaller variations, which are possiblymainly determined by sterics.
An article published by Indian Academy of Sciences. and also available at DOI 10.1007/s12039-016-1065-5
Olefin oxidation, epoxidation, computational, mechanisms
J. Chem. Sci.Vol. 128, No. 5, May 2016, pp. 707–718. DOI 10.1007/s12039-016-1065-5