(629h) Investigating the Origins of Selectivity Toward Maleic Anhydride during the Oxidation of Levulinic Acid over Supported Vanadium Oxides

Levulinic acid (LA) is a lignocellulosic platform molecule that enables production of bio-based fuels and chemicals. For example, we have previously reported that levulinic acid oxidation over supported vanadium oxides will produce maleic anhydride (MA) in high yield (71%). This transformation requires preferential oxidative scission of the methyl α-carbon at the keto group of levulinic acid as opposed to the internally positioned α-carbon in the methylene bridge. The high selectivity toward methyl scission during levulinic acid oxidation is unexpected based on trends observed during analogous oxidative scission of monofunctional methylketones. For example, during oxidation of 2-pentanone over supported vanadium oxides, one observes nearly complete selectivity toward scission of the internal methylene bridge. Aiming at understanding the difference in anomalous selectivity toward the terminal, methyl scission during the oxidation of levulinic acid, we compare reactivity and selectivity trends during the oxidative scission of various model ketones in a packed bed reactor (PBR). Our results suggest that abstraction of a hydrogen atom from the ketone α-carbon is necessary to facilitate oxidative scission. We additionally employ in situ FTIR spectroscopy to elucidate reaction and surface intermediates during ketone oxidation over supported vanadium oxides and to provide insight into unique reaction pathways occurring during the oxidation of levulinic acid. We highlight the role of previously unidentified hydrogen-deficient heterocycles in facilitating production of maleic anhydride during levulinic acid oxidation.