Synthesis and characterization of a new hydroxyl functionalized diacidic ionic liquid as catalyst for the preparation of diester plasticizers

Two new functionalized diacidic ionic liquids (FDAILs) including hydroxyl functionalized diacidic ionic liquid (HFDAIL) and sulfonated diacidic ionic liquid (SFDAIL) were synthesized and characterized by 1HNMR, 13CNMR and FT-IR. The catalytic activities of these FDAILs were examined in esterification reaction of anhydrides with some alcohols to give corresponding dialkyl plasticizers under solvent-free conditions. The results indicate that HFDAIL, as hydroxyl-bearing catalyst, show better catalytic performance. Under the optimum conditions, using HFDAIL, the conversion of phthalic anhydride was high and diester plasticizers were obtained with good to excellent yields in the presence of only 10 mol% of ionic liquid. All the produced diesters could be easily recovered due to their immiscibility with the ionic liquid. Recycling experiments suggests that these ionic liquids can be reused several times without remarkable loss in their catalytic activity.