Participation of new active species in epoxidation with cetylpyridinium dodecatungstate/FAp/urea–H2O2 system

We have developed an efficient catalytic solid-phase system for epoxidations that uses cetylpyridinium dodecatungstate ((CetylPy)10[H2W12O42]) catalyst/fluorapatite (FAp) disperse phase with a solid urea–hydrogen peroxide complex (urea–H2O2). The solid system was reusable and retained its high catalytic activity, although the catalyst was not fixed on the solid-phase. The reaction rate was first-order with respect to substrate concentration and amount of the catalyst. The solid-phase activation of polyoxometalates with urea–H2O2 was studied using FT-IR and solid-state NMR spectroscopy, and no known degraded peroxo-species was observed to form. Based on these kinetic and spectroscopic studies, we propose that the active species is a new, stable peroxo-species with the framework of the parent dodecatungstate, of which the terminal W(double bond; length as m-dashO)2 site is specifically transformed to peroxo-type of Wdouble bond; length as m-dashO(O2), in the system. Much higher efficiency of the dodecatungstate compared with the phsphotungstate or the decatungstate is considered to be due to the non-degraded, site-specific peroxo-species.