Aromatic hydrogenation of benzyl alcohol and its derivatives using compressed CO2/water as the solvent

A green approach to the aromatic hydrogenation of benzyl alcohol and its derivatives to produce cyclohexanemethanol was demonstrated in this report. In this work, the hydrogenation reactions were carried using neat, CO2-expanded liquid (CXL), water and compressed CO2/water, as the solvents. It was found out that using water as the solvent achieved the highest yield of the hydrogenation product (>96%). On the other hand, using the compressed CO2/water system as the solvent significantly enhanced the reaction rate (only 1/5 of the reaction time needed for total conversion when compared to reactions in water) while still maintained high product yield (>90%). It is believed that CO2 molecules dissolved in water could form carbonic acid simultaneously and the acid was proved to act as a promoter throughout the reaction.