Ammonium Phosphotungstate Bonded on Imidazolized Activated Carbon for Selective Catalytic Rearrangement of α-Epoxypinane to Carveol

Carveol is a rare fine chemical with specific biological activities and functions in nature. The artificial synthesis of carveol from plentiful and cheap turpentine is expected to further improve development of pharmaceutical and industrial applications. A new green catalytic system for the preparation of high-value carveol from α-epoxypinane is presented. A novel ammonium salt solid acid (AC-COIMI-NH4PW) was obtained from phosphotungstic acid bonded with imidazole basic site on nitrogen-doped activated carbon which, after ammonia fumigation, presented an excellent catalytic performance for the selective rearrangement of α-epoxypinane to carveol in DMF as solvent under mild reaction conditions. At 90 °C for 2 h, the conversion of α-epoxypinane could reach 98.9% and the selectivity of carveol was 50.6%. The acidic catalytic sites exhibited superior durability and the catalytic performance can be restored by supplementing the lost catalyst. Based on the investigation of catalytic processes, a parallel catalytic mechanism for the main product was proposed from the rearrangement of α-epoxypinane on AC-COIMI-NH4PW.