Brøsted acidic pyridinium-based ILs catalyzed the selective dimerization of isobutene: Performance and in-situ NMR study

Brøsted acidic pyridinium-based ILs of [NS][CF 3 SO 3 ] and [NS][HSO 4 ] have been synthesized for oligomerization of isobutene with the excellent conversion of 92.8% and the good selective dimerization at the temperature of below 100 °C. Hydroxyl-containing materials, especially ethanol, could facilitate catalytic activities to excellent conversions of isobutene and 84.2% selectivity of diisobutene. [NS][CF 3 SO 3 ] could be recovered by a simple liquid-to-liquid separation and reused more than ten times without obvious loss of catalytic activities. The formation process of oligomers has been examined by in-situ NMR spectroscopy, and a step-by-step generation process of carbonium ions varying from C 4 + , C 8 + to C 12 + was proposed. The work behaves the significance of constructing a better catalysis system for highly selective dimerization of isobutene, and potential being scaled-up for industrialization.