Functionalized dicationic ionic liquids: Green and efficient alternatives for catalysts in phthalate plasticizers preparation

Two highly acidic, imidazolium-based, functionalized dicationic ionic liquids (FDCILs) were synthesized and characterized by FTIR, H-1 NMR and C-13 NMR. The synthesized FDCILs were used as efficient and green catalysts in the synthesis of phthalate plasticizers through esterification of phthalic anhydride (PhA) with ethanol, n-propanol and n-butanol. Among these two FDCILs, (dimethyl-4-sulfobutyl-ammonium) 1,2-ethan-1-methyl-imidazolium-sulfonic acid hydrogen sulfate performed better. The catalytic activity of FDCIL is related to the density of acidic groups on it and the length of the carbon chain in the cationic part. The influences of the reaction temperature, catalyst dosage, and molar ratio of phthalic anhydride to alcohol on the esterification reaction were investigated. The reusability of the catalyst in these reactions was studied too. The diester phthalates were obtained up to 98.8% yield. The products can be separated easily by decantation from the reaction mixture.