(19d) Tuning Performance of Ketone Partial Oxidation over Supported VOx and Its Utilization: Selective Maleic Anhydride Production from Levulinic Acid Oxidative Scission.

Aerobic partial oxidations are crucial for producing commodity and specialty chemicals. In many industrial applications, vanadium oxide catalysts are used to effect partial oxidations; however, the desired reactions often suffer poor selectivity losses to combustion. In this study, we consider ketone partial oxidation, namely oxidative scission, to produce carbonyl and carboxyl fragments. We consider the impact of support, solvent, vanadate structure, and ketone structure in dictating performance. Specifically, we examine the performance of various mono- and polyvanadate structures supported on SiO₂, γ-Al₂O₃, TiO_2, and CeO₂. Structures of each catalyst were characterized using Raman and/or DR-UV-Vis spectroscopy. Interestingly, we observe that while support and vanadium oxide structure have a significant impact on activity, oxidative scission selectivity is largely invariant. Further investigations with a range of methyl ketone probe molecules having different degrees of a-carbon substitution revealed further insights about the influence of ketone structure on oxidative scission selectivity. Finally, we turn our attention to suppressing combustion, and we observe that water is beneficial in this regard. Specifically, it enhances oxidative scission rates, suppresses combustion rates, and mitigates catalyst deactivation.

Toward potential applications, we study the oxidative scission of bio-based levulinic acid. We observe that oxidation of either affords maleic anhydride in excellent yields (60-70%), which contrasts expectations based on trends observed for monofunctional methyl ketones. An examination of primary, secondary, and tertiary reaction pathways during oxidative scission of levulinic acid reveals that its facile intramolecular dehydration leads to the formation of stable, cyclic angelicalactones, which quickly dehydrogenate to form protoanemonin—a polyfunctional molecule having both diene and lactone structures. Its unique structure suggests it may be a useful platform chemical in the synthesis of biopolymers; further, its formation is unique to this 5-carbon system, and its formation underlies the high selectivity to maleic anhydride observed in this system.