Microwave-induced base-catalyzed synthesis of methyl levulinate, a further improvement in dimethyl carbonate-mediated valorization of levulinic acid

We report base-catalyzed upgrading of bio-based levulinic acid to methyl levulinate fuel additive with the assistance of microwave (MW) irradiation. During the reactions, formation of crystalline sodium, potassium, rubidium levulinate intermediates occurred. The methylation potential of dimethyl carbonate was found to be excellent at 120 °C under MW conditions; moreover, alkylation could also occur at the boiling point (∼90 °C) of solvent. Precipitation of levulinate salts could be reduced by addition of co-solvents, and thus yields of methyl levulinate increased to over 90 %. The detailed investigation of effects of MW-assisted reaction revealed the accelerated formation of metal levulinates and the behavior of levulinate salts, base catalysts as "molecular radiators". This allows us to focus on replacement of generally used K2CO3 catalyst (showing MW-enhanced decomposition though CO2 liberation). Several inorganic bases were tested and K3PO4 proved to be the best green and economically friendly alternative with higher reusability potential.