Highly efficient metal salt catalyst for the esterification of biomass derived levulinic acid under microwave irradiation

The esterification of levulinic acid ( LA) to alkyl levulinates has been investigated in the presence of various metal salt catalysts under microwave irradiation. The reaction obtained 99.4% yield of methyl levulinate (ML) in the presence of Al-2(SO4)(3) catalyst in methanol solution under microwave conditions. The optimized reaction conditions were 110 degrees C and 10 minutes with a 20 mol% catalyst loading. Alcohols with longer carbon chains showed lower reactivities in the microwave electromagnetic field due to their poorer abilities to absorb and transmit microwave energy. Moreover, microwave irradiation provided a significantly higher reaction rate compared to conventional oil bath heating. LA aqueous solution was also converted to ML with high yields. The Al-2(SO4)(3) catalyst was successfully applied to the esterification of other biomass derived organic acids to their corresponding esters in high yields. Finally, the catalyst was recycled 5 times without much decrease in activity.