Advance in the study of limonene epoxidation with H2O2 catalyzed by Cu(II) complex heteropolytungstates

The complex heteropolyoxotungstates of formula K-10[M-4(H2O)(2)(PW9O34)(2)]center dot 20H(2)O (PWM) with M=Co(II), Zn(II), Cu(II) and Mn(II), and their precursor, Delta-Na8HPW9O34 center dot 19H(2)O (Delta-PW9), were evaluated as bulk in limonene epoxidation using H2O2 as oxidant, 1,2 dicloroethane as solvent and metiltricaprilamonium chloride (Aliquat 336) as a phase transfer agent at 2 degrees C. In these biphasic conditions PWCu was the most active phase. Subsequently this phase was supported on gamma-Al2O3, the metal load was determined by AAS, ICP and X-ray fluorescence and the preservation of PWCu structure was confirmed by XPS and Raman microprobe. PWCu/gamma-Al2O3 was evaluated at 70 degrees C with acetonitrile as solvent. The pure PWCu showed a higher conversion to epoxide but lower selectivity due to the formation of secondary products. (C) 2012 Elsevier B.V. All rights reserved.