Abstract: Catalytic synthesis of2,5-dimethyl-2,4-hexadiene by Prins condensation of iso-butanal and tert-butyl alcohol was investigated using Brønsted acidic ionic liquids as both catalyst and solvent. It was found that all the ionic liquids were active for Prins condensation. After reaction, the upper organic phase could be easily separated from the ionic liquid by decantation. The ionic liquids could be reused in the next run by heat treatment under vacuum. Manipulating the structure of ionic liquids with respect to the organic cation or the organic/inorganic anion had great effects on the catalytic performance of the ionic liquids.

Key words: ionic liquid, Brø, nsted acid, iso-butanal, tert-butyl alcohol, Prins condensation, 5-dimethyl-2, 4-hexadiene