Esterification Catalyzed By Ionic Liquids

Three kinds of novel environmental-friendly plasticizers have been successfully synthesized by esterification using a series of acidic ionic liquids as catalysts. The catalytic activity of different ionic liquids have been examined and compared. Then we have selected several kinds of ionic liquids which are of excellent catalytic activities and can be reused after the esterification. We have also studied the optimum reaction conditions of synthesizing the novel plasticizers, including the reuse performances of the ionic liquids.Ten kinds of ionic liquids were synthesized and their structures were examined by IR and NMR. And the Br?nsted acidic and acidity of the ionic liquids have been researched through IR, the thermal stabilities of the ionic liquids have been examined by TG. The results showed that the ionic liquids are of strong acidic and good thermal abilities.For the synthesis of 1,2-cyclohexane dicarboxylates and TBC, three kinds of HSO3-functionalized ionic liquids, [HSO₃-pN(C₂H₅)₃]HSO₄, [HSO₃-pmim]HSO₄ and [HSO3-pmim]PTSA, showed better catalytic activity compared to the other acidic ionic liquids. They also showed good reuse performances since they could be easily separated from the products after reaction. The reaction conditions of using these Br?nsted acidic and HSO3-functionalized ionic liquids were determined by single factor experiments.The optimum reaction conditions of synthesizing dibutyl 1,2-cyclohexane dicarboxylates(DBCH) using ionic liquids as catalysts was studied. And the results were determined as follows: molar ratio of butanol to hexahydrophthalic anhydride(HHPA) was 2.5:1, amount of catalyst was 1 % (based on the mass of HHPA), reaction temperature was 130-150 oC, reaction time was 8 h.The condition of synthesizing dioctyl 1,2-cyclohexane dicarboxylate (DIOCH) using ionic liquids as catalysts was studied. The optimum reaction conditions of esterification were determined as follows: molar ratio of isooctanol to HHPA was 2.5:1, amount of catalyst was 1 % (based on the mass of HHPA), reaction temperature was 170-190 oC, reaction time was 4 h.The condition of synthesizing tributyl citrate (TBC) using ionic liquids as catalysts was studied. The optimal reaction conditions of esterification were determined as follows: molar ratio of butanol to citric acid(CA) was 4.5:1, amount of catalyst was 1 % (based on the mass of CA), reaction temperature was 130-150 oC, reaction time was 8 h.Under the optimal reaction conditions, [HSO3-pN(C2H5)3]HSO4 and [HSO₃-pmim]PTSA were more suitable for the synthesis of DBCH and they could both be reused at least 4 times with the conversion not less than 90 %. [HSO₃-pN(C₂H₅)₃]HSO₄ and [HSO₃-pmim]HSO₄ were more applicable for the synthesis of dioctyl 1,2-cyclohexane dicarboxylate and could be reused at least 6 times with the conversion around 93 %. [HSO₃-pmim]HSO₄ and [HSO₃-pN(C₂H₅)₃]HSO₄ could be reused 5 times with the conversion above 96 % for the synthesis of TBC.The environmental-friendly plasticizers synthesized were characterized by IR, MS, NMR and GC. The purity of DBCH was 99.30 %, while DIOCH was 98.86 % and TBC was 99.76 %. Thermal decomposition temperature was determined by TG analysis. DIOCH began to decompose at 280 oC, and DBCH started to decompose at 218 oC. The acute mice oral toxicity results of both DBCH and DIOCH were LD₅₀ >10,000mg/kg, indicating that DBCH and DIOCH were actual non-toxic. Thus DBCH and DIOCH could be used as environmental-friendly plasticizers. And the appearance, color, acid value, odor, viscosity and refractive index of the products were also studied.