A Brønsted-Lewis Acidic Ionic Liquid: Its Synthesis and Use as the Catalyst in Rosin Dimerization

Brønsted-Lewis acidic ionic liquids 1-(3-sulfonic acid)-propyl-3-methylimidazole chlorozincinates ([HO3S-(CH2)3-mim]Cl-ZnCl2) were synthesized and characterized. The characterization results indicated that [HO3S-(CH2)3-mim]Cl-ZnCl2 (molar fraction of ZnCl2x > 0.5) had both Brønsted and Lewis acid properties. The catalytic properties of these ionic liquids were investigated using the dimerization of rosin, and it was shown that ionic liquid [HO3S-(CH2)3-mim]Cl-ZnCl2 (x = 0.64) was a good catalyst. Under the optimum conditions for polymerization, i.e., rosin 5.0 g, toluene 15 g, the mass fraction of ionic liquid 5%, reaction temperature 110 °C, and reaction time 4 h, a product with the softening point of 118 °C was obtained. It was also found that the product was easily separated from the reaction mixture and the ionic liquid catalyst had good reusability.