Synthesis of 2,4-diisopropyl-5,5-dimethyl-1,3-dioxane catalyzed by Brønsted acidic ionic liquids

The acetalization reactions of isobutyraldehyde with 2,2,4-trimethyl-1,3- pentanediol (TMPD) for the synthesis of 2,4-diisopropyl-5,5-dimethyl-1,3-dioxane were carried out under mild reaction conditions using four water-stable Brønsted-acidic task-specific ionic liquids ([HMIM]BF₄, -SO₃H functionalized acidic ionic liquid, -COOH functionalized acidic ionic liquid, [NMP][HSO₄]) as environmentally benign catalysts for the first time. The process is highly effective and very selective. The -COOH functionalized Brønsted acidic ionic liquid with the two acid sites (IL-3) exhibited the most excellent catalytic performance under mild reaction conditions. The -COOH functionalized Brønsted acidic ionic liquid could be conveniently separated from the product and easily recycled in subsequent runs.