Zirconia catalysts in Meerwein-Ponndorf-Verley reduction of citral

Zirconium-containing catalysts were found to be active in the Meerwein-Ponndorf-Verley (MPV) reduction of citral. Good activity and selectivity to the reduced alcohol, geraniol and nerol, were observed over hydrous zirconia and zirconium 1-propoxide supported on silica. In particular, hydrous zirconia calcined at temperatures below 300 °C was highly active. Hydrous zirconia catalysts modified by NaOH, NH4F, PO43− and SO42− had lower activity. Surface hydroxyl groups are postulated to be involved in ligand exchange with the reductant, 2-propanol. Zr-zeolite beta showed high activity, but poorer selectivity than the other two samples, due to subsequent dehydration of the product formed. For all catalysts, the trans-isomer of citral was preferentially reduced over the cis-isomer.