Investigation of Batch Alkene Epoxidations Catalyzed by Polymer-Supported Mo(VI) Complexes

Abstract

Polymer-supported Mo(VI) catalysts (PBI.Mo and Ps.AMP.Mo) have been prepared and characterized. The activities of both of these catalysts in epoxidation of alkenes (e.g., cyclohexene; 1-octene; limonene; α-pinene) with dry tert-butyl hydroperoxide (TBHP) as oxidant have been studied under different reaction conditions in a batch reactor. The long-term stability and Mo leaching of each polymer catalyst was also assessed by recycling a sample in batch reaction using conditions that will form the basis of a continuous process. Both catalysts have been shown to be sufficiently stable to be considered as real candidates for use in such a process. In the case of the PBI.Mo catalyst, the order of reactivity of the alkenes was found to be the following: cyclohexene > limonene > α-pinene > 1-octene. “Wet” TBHP can also be used for cyclohexene epoxidation catalyzed by PBI.Mo without any significant decrease in the final TBHP conversion. In the case of limonene epoxidation, however, the presence of water reduced the TBHP conversion and also affected the cis−trans ratio of the main product 1,2-limonene epoxide. The reusability studies with PBI.Mo revealed that the largest fall in the final TBHP conversion was observed for α-pinene epoxidation among the alkenes studied. For 1-octene epoxidation, the loss of Mo from each support has been investigated by isolating any residue from the reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions.