Abstract:

Esterification reaction of boric acid, pinacol and cyclohexanol has been studied in ionic liquids(IL), including 1-methyl-2-pyrrolidonium hydrogen sulfate([Hnmp]HSO4), 1-butyl-3-methylimidazolium tetrafluoroborate([Bmim]BF4) and 1-butyl-3-methylimidazolium hexafluorophosphate([Bmim]PF6). The influences of the types of ionic liquids, reaction temperature, reaction time and molar ratio of reactants to IL on the yields of 2-cyclohexyloxy-4,4,5,5-tetramethyl-[1,3,2]dioxaborolan have been investigated. The results showed that under the optimized conditions[n(boric acid)∶n(pinacol)∶n(cyclohexanol)∶n([Hnmp]HSO4)=1∶1∶1∶1, 70 ℃ and 4 h], the yield of 2-cyclohexyloxy-4,4,5,5-tetramethyl-[1,3,2]dioxaborolan could reach up to 72.5%. The ionic liquid can be used repeatedly for four times without remarkable loss of the catalytic activity.

Key words: ionic liquid, esterification, boric acid ester, green chemistry