Catalytic properties of heteropoly compounds in 1,3-butadiene oxidation with hydrogen peroxide

The homogeneous oxidation of 1,3-butadiene (BD) in H₂O₂-HPC-CH₃CN (HPC = heteropoly compound) solutions has been investigated. The route of the reaction depends on the nature of the metal capable of coordinating with active oxygen in the HPC. The products of radical BD oxidation (acrolein, 3-butene-1,2-diol, 2-butene-1,4-diol, furan) form in the presence of H_3+n PMo_{12 ? n} V _n O₄₀ (n = 1, 2) acids. 3,4-Epoxy-1-butene (EB) and acrolein + furan, which form in equal amounts in the presence of the (n-Bu₄N)₅PW₁₁O₃₉Fe(OH) salt, result, respectively, from the electrophilic addition of hydrogen peroxide to BD and from radical BD oxidation on iron-oxygen complexes in the HPC composition. The reaction carried out in the presence of (n-Bu₄N)₃{PO₄[WO(O₂)₂]₄}, (n-Bu₄N)₅Na_0.6H_1.4PW₁₁O₃₉, or (EMIm)₅NaHPW₁₁O₃₉ yields EB with high selectivity on the reacted BD basis (up to 97%) and H₂O₂ (about 100%). The formation and conversion of the phosphotungstate peroxo complexes PW _n O _m ^α? (n = 2, 3, 4) that are active in BD epoxidation have been investigated by ³¹PNMR spectroscopy. The role of the tetrabutylammonium and ethylmethylimidazolium cations in the formation of these complexes has been demonstrated.