Catalytic Synthesis And Plasticity Of Citric Acid Esters

Research of ionic liquids as catalyst on the synthesis of citric acid esters was one of the hotspot in the esterification of citric acid. Six ionic liquids were selected and synthesized. Tributyl citrate(TBC), Triethyl citrate(TEC), Trimethyl citrate(TMC) were synthesized by the catalysis of ionic liquids and H2SO4 and the reaction conditions were studied respectively.. Their plasticity on epoxy resin cure was tested.1-Methyl-imidazolium hydrogen sulfate([Hmim]+[HSO4]-), Hydrogen sulfate ([Hpyro]+[HSO4]-), 1-Methyl-3-(3-sulfoproply)-imidazolium hydrogen sulfate ([HSO3-pmim]+[HSO4]-), 1-Methyl-3-(4-sulfobutyl)-imidazolium hydrogen sulfate ([HSO3-bmim]+[HSO4]-), 1-(3-Sulfopropyl)-pyridinium hydrogen sulfate ([HSO3-pPydin]+[HSO4]-), 1-(3-Sulfobutyl)-pyridinium hydrogen sulfate ([HSO3-bPydin]+[HSO4]-), were prepared, and characterized with IR, 1H-NMR and TG-DSC.The catalytic activity and reuse performance of six ionic liquids on the synthesis of Tributyl citrate were researched. The acidic functionalized ionic liquids [HSO3-pmim]+[HSO4]-, [HSO3-bmim]+[HSO4]-, [HSO3-bPydin]+[HSO4]- showed good catalytic activity. Under optimum conditions, the conversion of carboxyl were more than 99%. And [HSO3-bPydin]+[HSO4]- has the best reuse performance. When the ionic liquids dosage was 15%w, [HSO3-bPydin]+[HSO4]- can be reused 15 times with the conversion of conversion of carboxyl not less than 98% stablely.Among the ionic liquids used in synthesis of Triethyl citrate(TEC), the acidic functionalized ionic liquids [HSO3-bPydin]+[HSO4]– which with both good performance and reuse performance was choosed. The optimum conditions were obtained as follows: n(ethanol):n(citrate)=6 : 1, catalyst amount 8% (according to total weight of reactant), ethanol was added in 3 times, and reaction time was 2 h. The catalyst was reused for 23 times, and the conversion of carboxyl was higher than 98%.H2SO4 used for the catalyst of systhesis of Trimethyl citrate (TMC) was studied. The obtained optimum reaction conditions were as follows: methanol was added in 3 times, reaction time3h, catalyst amount 0.85%(according to total weight of reactant), n(methanol) : n(citric acid) =6 : 1. Under the optimum conditions, yield of product was up to 77.1% and acid value was 4 mg/g.The plasticity of TBC and TEC was studied. The results of the tests indicated that both products have good plasticized performance which compared with common plasticizer dibutyl phthalate(DBP).