ALKENE EPOXIDATIONS CATALYZED BY MO(VI) SUPPORTED ON IMIDAZOLE-CONTAINING POLYMERS .2. RECYCLING OF POLYBENZIMIDAZOLE-SUPPORTED MO(VI) IN THE EPOXIDATION OF CYCLOHEXENE

Mo(VI) has been supported on a polybenzimidazole resin and used as an epoxidation catalyst in the reaction of t-butylhydroperoxide (TBHP) with cyclohexene. A preliminary kinetic study has suggested that mass transfer of TBHP might be rate-limiting. The experimental activation energy is higher than that of an analogous homogeneous reaction catalysed by MoO(2)acac(2). Nevertheless, the supported catalyst is highly active and has been recycled nine times with no detectable loss of Mo from the support, but with a decline in activity. Activation of the polymer catalyst by pretreatment with TBHP far periods up to 48 h does not influence the activity of the catalyst on first use; however, higher activity is retained on recycling. The imidazole ligand on the polymer appears to bind the Mo centres very effectively and Mo leaching is not responsible for the decay in activity on recycling. The most likely explanation for this is the blockage of access to catalytic sites in the polymer by accumulation of side-products (oligomer) from cyclohexene or its epoxide. (C) 1995 Academic Press, Inc.