Tunable dimerization of α-methylstyrene catalyzed by acidic ionic liquids

Dimerization of α-methylstyrene (AMS) catalyzed by ionic liquids and the effects of different organic solvents on the catalytic reaction were investigated. The results show that ionic liquids such as alkylaminium-chloroaluminate and alkylaminium-ferric chloride are effective catalysts for the dimerization. AMS conversion of 100% was achieved when using alkylaminium-chloroaluminate chloride as catalyst. The selectivity of saturated dimer 1,1,3-trimethyl-3-phenylindan is as high as about 97% in the absence of organic solvents. Moreover, the raw material was mainly converted to unsaturated dimers 4-methyl-2,4-diphenyl-1-pentene and 4-methyl-2,4-diphenyl-2-pentene in the presence of several polar solvents such as tertiary amyl alcohol or tertiary butanol, although the reaction rate of the AMS conversion became much lower. Thus, AMS dimerization can be tuned to produce either cyclic dimers or linear dimers by adding polar solvents or omitting them.