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‐[M 4 (H 2 O) 2 (PW 9 O 34 ) 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 Mn 4 (PW 9 ) 2 , affording 6,7-epoxide at 82% selectivity. Linalyl acetate 1,2-epoxide was the major product with 51% and 77% selectivity for Co 4 (PW 9 ) 2 and Fe 4 (PW 9 ) 2 , respectively. Oxidation of carveol occurred with very good conversions in the presence of Mn 4 (PW 9 ) 2 , Co 4 (PW 9 ) 2 and Fe 4 (PW 9 ) 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.