Spontaneous Biphasic System with Lithium Chloride Hydrate for Efficient Esterification of Levulinic Acid

Abstract

An efficient approach for synthesis of levulinate from biomass‐derived levulinic acid (LA) and n‐butyl alcohol (BuOH) in molten salt hydrates (MSH) with microwave irridiation was reported. A series of molten salt hydrates were evaluated in terms of their catalytic activity and pH value without any additional catalyst. Introduction of AlCl3 greatly increased the yield of butyl levulinate(BL). As high as 95.5 % BL yield was obtained in LiCl ⋅ 3H2O+AlCl3 system. Reaction mechanism study shows that LiCl ⋅ 3H2O can promote the esterification of LA with BuOH by enhancing the protonation of LA. LiCl is able to expel the formed BL into organic‐phase, and then boost up esterification efficiency. Both separation of BL and strong hygroscopicity of LiCl ⋅ 3H2O promoted the esterification reaction equilibrium. High‐efficient esterification of LA with BuOH realized separation of LA from MSH. Activation energies of BL formation are 70.9 kJ/mol in LiCl ⋅ 3H2O and 31.8 kJ/mol in AlCl3+LiCl ⋅ 3H2O.