H3PMo12O40 Heteropolyacid: A Versatile and Efficient Bifunctional Catalyst for the Oxidation and Esterification Reactions

Abstract

This work summarises our recent developments for H2O2-based green oxidation reactions and the results obtained in esterification reactions, both catalysed by H3PMo12O40 and their salts. We have found that these catalysts are versatile bifunctional catalysts, highly active in esterification reactions as well as oxidation reactions. Herein, their performance was assessed in three different kinds of reactions: natural olefin oxidation, gasoline oxidative desulfurisation reactions and acid-catalysed esterification of fatty acids. The H3PMo12O40 catalyst has two key features which allow it to act efficiently in all these reactions: Bronsted and Lewis acid sites and redox sites. At first, H3PMo12O40-catalysed oxidation reaction of dibenzothiophene (DBT) into dibenzosulphone (DBTO) by hydrogen peroxide was investigated in a biphasic system (i.e. isooctane/acetonitrile). The DBT is soluble only in the non-polar layer (isooctane); thus, after their oxidation into DBTO, this later migrates to polar layer (acetonitrile). This is very useful process for the removal of sulfur compounds, usually found in gasoline samples. Surprisingly, the AlPMo12O40 heteropolyacid salt was found to be more efficient than H3PMo12O40 catalyst in DBT oxidation reactions. To the best of our knowledge, this is the first application of AlPMo12O40 catalyst for mentioned oxidation reactions without using phase-transfer agent. High removal rates (higher than 90 %) were achieved using AlPMo12O40 as catalyst and hydrogen peroxide as oxidant. On the other hand, studying the second oxidative process, we have found that H3PMo12O40/H2O2 system was also highly effective in oxidation reactions of monoterpenes. Monoterpenes are abundant and renewable raw materials and were converted into oxygenates products which are valuable ingredient for fragrance, agrochemicals and pharmaceutical industries. Camphene was selectively oxidised into epoxy and allylic products with conversion rates on the range 80–90 f . Hydrogen peroxide, an environmentally benign reactant, was employed as oxidant in the camphene oxidation reactions. Finally, we also have described novel results of H3PMo12O40-catalysed fatty acid esterification reactions with different alcohols.