Investigation of induction times, activity, selectivity, interface and mass transport in solvent-free epoxidation by H2O2 and TBHP: a study with organic salts of the [PMo12O40](3-) anion

The phosphomolybdate salts Q(3)[PMo12O40] [Q = tetra-n-butylammonium (TBA), n-butylpyridinium (BP), cetylpyridinium (CP)] have been used as catalysts for the epoxidation of cyclooctene under organic solvent-free conditions, using H2O2 or t-BuOOH (TBHP) in water as oxidants, and compared with the BP salt of the analogous tungsten derivative, (BP)(3)[PW12O40]. High catalytic activities have been recorded down to very low catalyst loadings (2 ppm). The activity and selectivity depend on the nature of the oxidant and the cation. The dominant process appears to be homogeneous and this rationalizes, together with the evolution of the phase equilibria, the presence of an induction period for the epoxidation by H2O2 and the evolution of the epoxide selectivity. The recovered catalysts are reusable and exhibit equivalent reactivity.