Synthesis of diethyl oxalate catalyzed by acidic ionic liquids

Four imidazolium-based acidic ionic liquids were synthesized and used as catalysts for the synthesis of diethyl oxalate by esterification of oxalic acid with ethanol.The effects of several operation conditions were investigated.The optimal reaction conditions were as follows:[Mim(CH2)3SO3H]HSO4 as catalyst,reaction temperature 110 ℃,reaction time 90 min,mole ratio of ethanol and oxalic acid 4∶1,under such conditions the yield of diethyl oxalate was over 73%,and the ionic liquid could be recycled at least four times without obvious deactivation.Additionally,the ionic liquid [Mim(CH2)3SO3H]HSO4 was immobilized on silica by the sol-gel method.The results showed that the supported ionic liquid exhibited higher catalytic performance than the unsupported one,with a yield of diethyl oxalate up to 84.8%.