• RICHARD TIA

      Articles written in Journal of Chemical Sciences

    • Quantum chemical study of the mechanisms of oxidation of ethylene by Molybdyl and Tungstyl Chloride

      RICHARD TIA EVANS ADEI JOSEPH BAIDOO JULIANA EDOR

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      The mechanisms of oxidation of olefins with $MoO_{2}Cl_{2}$ and $WO_{2}Cl_{2}$ are studied with DFT. Theformation of epoxide from these reactions is not very feasible by any of the postulated paths. If the epoxideprecursor will form at all, it will arise via initial $[3+2]_{O},_{Cl}$ addition of ethene to $MoO_{2}Cl_{2}$ and $WO_{2}Cl_{2}$ to 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 $[3+2]_{O},_{Cl}$ addition ofethene to $MoO_{2}Cl_{2}$ . 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 energeticallyfeasible with $MoO_{2}Cl_{2}$ , but appears thermodynamically plausible with WO2Cl2. Thus, the oxidation ofethylene with $MoO_{2}Cl_{2}$ will most likely lead to the formation of chlorohydrins predominantly via $[3+2]_{O},_{Cl}$ addition; oxidation with WO2Cl2 may also form chlorohydrins, but only extremely slowly. The oxyhalidesMO2Cl2 become weaker oxidants in the order CrO2Cl2 >>$MoO_{2}Cl_{2}$ >$WO_{2}Cl_{2}$ . Corresponding to this, reactionsinvolving 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.

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