HOMOGENEOUS VS HETEROGENEOUS CATALYSIS OXIDATION OF LIQUID CYCLOHEXENE CATALYZED BY IONS AND OXIDES OF TRANSITION METALS

Liquid-phase autoxidations of cyclohexene at 70 ° in the presence of soluble acetylacetonates of the first-row transition metals are compared with similar autoxidations in the presence of insoluble oxides of the same metals. The distributions of volatile products (cyclohexene oxide, cyclohexenone, cyclohexenol, and cyclohexenyl hydroperoxide) closely follow the patterns observed for the decompositions of cyclohexenyl hydroperoxide in the presence of the same metal catalysts. Whereas several of the metals give nearly equal quantities of cyclohexenol and cyclohexenone, chromium(III) and iron(III) give significantly more ketone than alcohol, and vanadium and molybdenum give large proportions of epoxide. The pattern suggests that all of the observed oxidations are free-radical chain reactions having the same homogeneous propagation steps and yielding, as the principal primary product, cyclohexenyl hydroperoxide, which then undergoes metal-catalyzed decomposition. Strong parallelism is noted between the product distributions in the homogeneous oxidations and those in the heterogeneous oxidations involving the corresponding metals, leading to the conclusion that for the system studied, the atomic number and oxidation state of the transition metal in the catalyst is more important than the detailed catalyst structure in determining the course of the reaction. © 1969.