Green and moisture-stable Lewis acidic ionic liquids (choline chloride · xZnCl2) catalyzed protection of carbonyls at room temperature under solvent-free conditions

Choline chloride · xZnCl2 (x = 1–3) or benzyltrimethylammonium chloride · 2ZnCl2 have been used as efficient and recyclable catalysts for protection of carbonyls to 1,3-dioxolanes and 1,3-dioxanes at room temperature under solvent-free conditions. FT-IR investigation demonstrates the four ionic liquids have similar Lewis acid strength, which is in agreement with the activities observed in the acetalization reaction. The catalytic system choline chloride · 2ZnCl2 can be reused up to five times without appreciable loss of activity. The simple procedures as well as easy recovery and reuse of this novel catalytic system are expected to contribute to the development of more benign acetalization procedure of carbonyl compounds.