Solvent free synthesis of 7-isopropyl-1,1-dimethyltetralin by the rearrangement of longifolene using nano-crystalline sulfated zirconia catalyst

Nano-crystalline sulfated zirconia solid acid catalyst, synthesized by a one-step sol-gel method, was studied for the rearrangement of longifolene to isolongifolene and 7-isopropyl-1,1-dimethyltetralin under solvent free conditions. Kinetic H-1 NMR spectroscopic studies confirmed the formation of 7-isopropyl-1,1-dimethyltetralin through further rearrangement of isolongifolene in the presence of a higher number of acidic sites. the selectivity for the rearranged products namely isolongifolene and 7-isopropyl-1,1-dimethyltetralin was observed to be strongly influenced by the acidity of the catalysts in terms of Bronsted (B) and Lewis (L) acid sites ratio. The catalyst having a higher B/L ratio (5,6) showed higher selectivity (56%) for 7-isopropyl-1,1-dimethyltetralin. The selectivity for the products could also be controlled by longifolene to catalyst weight ration; for example, 100% isolongifolene could be obtained using less amount of the catalyst, whereas for 7-isopropyl-1,1-dimethyltetralin higher amount of catalyst was required. Thermally regenerated catalyst showed decreased selectivity for 7-isopropyl-1,1-dimethyltetralin due to a decrease in the B/L ration, which in turns influenced by loss of sulfur during the reaction. (C) Elsevier B.V. All rights reserved.