Catalytic liquid phase oxidation of p-xylene using transition metal substituted polyoxometalates

Abstract

Liquid phase oxidation of <i>p-</i>xylene has been carried out in the presence of potassium salts of monosubstituted heteropoly compounds with tungsten as the addenda atom and having the

general formulae [XW₁₁MLO₃₉]^8-n.x H₂O where X = P and Si , Mⁿ⁺ = Co²⁺, Cu²⁺ and Mn²⁺ and L = H₂O. The reactions are carried out in a halide free environment using air as the oxidant and water as the solvent at a temperature of 180°C. High values of <i>p</i>-xylene conversion to the order of 70% are obtained using K₆[SiW₁₁Co(H₂O)O₃₉].14 H₂O as catalyst The silicotungstate derivatives have been found to be more efficient catalysts than the phosphotungstate analogues for the oxidation of <i>p</i>-xylene. The product obtained is mainly <i>p</i>-toluic and terephthalic acids with minor quantities of <i>p</i>-tolualdehyde and <i>p</i>-methyl benzylalcohol. Influence of reaction parameters such as temperature, solvents and catalyst concentration on the oxidation reaction and its effect on product distribution have been examined.