Catalytic homogeneous oxidation of monoterpenes and cyclooctene with hydrogen peroxide in the presence of sandwich-type tungstophosphates [M4(H2O)2(PW9O34)2]n−, M = CoII, MnII and FeIII

Catalytic efficiency of tetrabutylammonium salts of sandwich tungstophosphates B‐α‐[M₄(H₂O)₂(PW₉O₃₄)₂]ⁿ⁻, M = Co^II, Mn^II, Fe^III, was studied in the oxidation of (R)-(+)-limonene, geraniol, linalool, linalyl acetate, carveol, and cis-cyclooctene with hydrogen peroxide, in acetonitrile. Oxidation of (R)-(+)-limonene gave limonene-1,2-diol as main product. Epoxidation of linalool takes place preferentially at the more substituted 6,7-double bond, the corresponding 6,7-epoxide reacting further, yielding furano- and pyrano-oxides, via intramolecular cyclization. Oxidation of linalyl acetate occurred preferentially at the more substituted 6,7-double bond for Mn₄(PW₉)₂, affording 6,7-epoxide at 82% selectivity. Linalyl acetate 1,2-epoxide was the major product with 51% and 77% selectivity for Co₄(PW₉)₂ and Fe₄(PW₉)₂, respectively. Oxidation of carveol occurred with very good conversions in the presence of Mn₄(PW₉)₂, Co₄(PW₉)₂ and Fe₄(PW₉)₂, yielding carvone and carveol 1,2-epoxide in similar amounts. Oxidation of cis-cyclooctene gave only the epoxide, while oxidation of geraniol at room temperature afforded 2,3-epoxygeraniol as the major product.