Lewis acidic deep eutectic solvents as catalysts for rosin polymerization

Abstract

A series of tunable Lewis acidic deep eutectic solvents (DESs) were prepared easily by self-assembly of different Lewis acids as hydrogen bond acceptors (HBAs) with hydrogen bond donors (HBDs), and their catalytic activity was investigated in the rosin polymerization reaction. The optimized DES [InCl₃]₄[ChCl] was further investigated owing to its excellent catalytic properties in the reaction. The formation of hydrogen bonds in the structure of [InCl₃]₄[ChCl] was confirmed by FT-IR and ¹H NMR spectroscopies. The factors affecting the rosin polymerization reaction were explored, and the optimum reaction conditions were rosin 15 g, toluene 5.4 mL, n-octane 12.6 mL, DES 5 g, 110 °C and 10 h. The softening point of the polymerized rosin could reach 149.9 °C, and the acid value was 124.5 mg KOH g⁻¹. Meanwhile, the DES catalyst could be recovered and reused for six runs without post-processing. The characterization of the polymerized product showed that the product was mainly a rosin dimer. The new catalytic system exhibits the advantages of low energy consumption, high efficiency and environmentally friendly nature, and provides a promising and sustainable approach for the preparation of polymerized rosin.