Abstract: A novel thermoregulated-acidic ionic liquid, 1-(3-sulfonic acid)-propyl-3-polyethylene glycol-yl imidazole dihydrogen phosphate ([PEOIM-SO₃H]H₂PO₄), was synthesized, characterized, and used as a catalyst in the hydration of α-pinene. The ionic liquid had good thermoregulated and acidic catalytic performance in the hydration. Under the optimum conditions of n(α-pinene):n(chloroacetic):n(water) = 1:1:5, α-pinene 0.06 mol, ionic liquid 3.0 mmol, reaction temperature 80 ^oC, and reaction time 8 h, the α-pinene conversion was more than 89% and the terpineol selectivity was 65.0%. When the ionic liquid was reused for five times, the α-pinene conversion reached 85.8% and the terpineol selectivity was 66.8%.

Key words: thermoregulated-acidic ionic liquid, α-pinene, terpineol, hydration, catalysis