Synthesis of ethyl p-hydroxybenzoate with ionic liquid [HSO_3-Pmim]HSO_4 immobilized on silica gel as catalyst

Ethyl p-hydroxybenzoate was synthesized with ionic liquid [HSO3-Pmim]HSO4 immobilized on silica gel as catalyst.Effects of reaction temperature,reaction time,molar ratio of alcohol to acid and dosage of immobilized ionic liquid on the product yield were investigated.Results indicated that ionic liquid [HSO3-Pmim]HSO4 immobilized on silica gel displays good catalytic action on the reaction for synthesis of ethyl p-hydroxybenzoate.After completion of the reaction,the catalyst can be easily separated from the reaction mixture by filtration during hot state.Under conditions as:molar ratio of alcohol to acid 3.5∶1,dosage of catalyst with respect to the acid 4%,reaction temperature 95 ℃ and reaction time with reflux 3 h,the yield can achieve higher than 92%.The catalyst can be reused for 5 cycles without significant loss of activity.