Elucidating the Role\nof Water on Limonene Oxidation\nwith H<sub>2</sub>O<sub>2</sub> over γ‑Al<sub>2</sub>O<sub>3</sub>

Limonene oxide, which is produced from limonene epoxidation,\nis\na valuable molecule that can be applied in flavor, fragrance, and\nrenewable polymer applications. A catalytic reaction system using\nH<sub>2</sub>O<sub>2</sub> with γ-Al<sub>2</sub>O<sub>3</sub> and ethyl acetate (EtOAc) as the solvent has been explored as an\neffective system for this reaction. In these previous studies, a number\nof postulates have been proposed as to how water affects the reaction;\ntherefore, the focus of this work is to elucidate the role of water\nin limonene epoxidation. While not impacting the selectivity to limonene\noxide, the amount of water in the reaction system is shown to significantly\nimpact the limonene reactivity. Furthermore, through both addition\nof excess water and removal of water with a Dean–Stark apparatus,\nthe control of the H<sub>2</sub>O<sub>2</sub>/H<sub>2</sub>O ratio\nis demonstrated to be the primary factor controlling reactivity. In\ncontrast, changes in limonene concentrations for a specific H<sub>2</sub>O<sub>2</sub>/H<sub>2</sub>O ratio are shown to have little\nimpact on the reaction rate. This study shows that the competitive\nadsorption of H<sub>2</sub>O<sub>2</sub> and water on the catalyst\nsurface is key in explaining the water impact on the reaction performance.