Catalytic synthesis of plasticizer tributyl citrate with solid superacid S_2O_8~(2-)/SnO_2-SiO_2

A non-toxic plasticizer tributyl citrate was synthesized by the reaction of citric acid with n-butanol using solid superacid S2O2-8/SnO2-SiO2 as the catalyst.Experiment results indicated that the optimum process conditions were as follows.The mole ratio of citric acid to n-butanol was 1∶4.The amount of catalyst was 2 percent of the mass of citric acid.The refluxing temperature was 120 ℃ and the reaction time was 4 h,with the esterification yield reaching up to 96.2%.The catalyst after having been used for 5 times,didn′t show significant decline in its activity.The qualitative analysis of product was carried out by using IR and NMR spectroscopy.The purity of product analyzed by GC was above 99.0%.