OLEFIN OXIDATION BY THE SYSTEM H2O2 MOO42- - COMPETITION BETWEEN EPOXIDATION AND PEROXIDATION/

The oxidation of tiglic acid by the catalytic system hydrogen peroxide /molybdate ions is investigated in water under varying conditions of p H. Using similar conditions of temperature and concentrations, we show that two different reaction pathways compete leading either to an epo xide in acidic medium or to an allylic hydroperoxide in alkaline mediu m. These results are interpreted in terms of the involvement of two pe roxomolybdates. Epoxidation probably proceeds via the tetraperoxodimol ybdate Mo2O3(O-2)(4)(2-) whereas peroxidation involves singlet oxygen, O-1(2), ((1) Delta(g)), formed as a result of the decomposition of th e triperoxomolybdate MoO(O-2)(3)(2-). Finally, experimental conditions are given to obtain selectively the epoxide or the hydroperoxide.