Esterification of Menthol and Lactic Acid by Silicotungstic Acid Catalyst Supported on Bentonite

The silicotungstic acid catalyst supported on bentonite was employed in the esterification of menthol and lactic acid. The main reaction parameters were silicotungstic acid loading on bentonite, the amounts of catalyst, molar ratio of reactants, reaction temperature and reaction time. The optimum conditions were determined as follows : silicotungstic acid loading on bentonite 50 wt %, catalyst 1.25 g, mole ratio of menthol to lactic acid 1:1.1, reaction temperature 130 degrees C and reaction time 3 h. The esterification yield of menthyl lactiate was about 83.97 %. The catalyst could be used repeatedly for many times without distinct loss in activity.