One-Pot Transformation of (R)-(+)-Citronellal over a Bifunctional Ni/ZnBr2/β-Zeolite Catalyst

The transformation of (R)-(+)-citronellal to isopulegols and menthols in a one-pot reaction was improved using a zeolite catalyst. The one-pot transformation of (R)-(+)-citronellal was studied through a Ni/ZnBr2/β-zeolite catalyst. The Ni/ZnBr2/β-zeolite catalyst was prepared by impregnating 15% ZnBr2 (w/w) and 15% Ni (w/w) on β-zeolite. The addition of Ni to the ZnBr2/β-zeolite catalyst resulted in a useful bifunctional catalyst that combined a high rate of cyclization of citronellal to isopulegols over ZnBr2 sites and subsequent hydrogenation to menthol over Ni sites. These catalysts were characterized using X-ray diffractometer (XRD) and scanning electron microscope-energy dispersive Xray spectrometer (SEM-EDX). Catalytic reactions were carried out at 120 °C with magnetic stirring under a 1 atm nitrogen atmosphere for 1 h (cyclization reaction) and maintained under a 1 atm hydrogen atmosphere for 4 h (hydrogenation reaction). Products of the reaction were measured using gas chromatography-mass spectrometer (GCMS) and gas chromatography (GC). The results showed that the Ni/ZnBr2/β-zeolite catalyst can transform (R)-(+)- citronellal to isopulegols and menthols in a one-pot transformation, with a selectivity to isopulegols of 73.8% and selectivity to menthols of 6.40%.