Hydrous Zirconia as a Selective Catalyst for the Meerwein–Ponndorf–Verley Reduction of Cinnamaldehyde

Hydrous zirconia was found to be active in the Meerwein–Ponndorf–Verley (MPV) reduction of cinnamaldehyde with 2-propanol. An initial selectivity to cinnamyl alcohol of higher than 97% was measured. At longer reaction times, etherification between cinnamyl alcohol and 2-propanol decreased the selectivity. The activity decreased sharply when the hydrous zirconia was calcined to higher temperatures. Surface hydroxyl groups are postulated to be important for the activity. They are required for ligand exchange with 2-propanol. Zirconium 1-propoxide grafted on silica, siliceous MCM-41, and Al-MCM-41 were also active in the MPV reaction. In contrast, zeolite beta, although active in the conversion of cinnamaldehyde, showed poor selectivity toward the desired product, cinnamyl alcohol. Instead, the main product formed was cinnamyl 2-propyl ether.