Alkylation of benzene with 2-chloropropane on chlorine-treated alumina

Abstract

The alkylation of benzene with chloropropanes on solid Lewis acid catalysts prepared by the chlorination of γ-alumina at 1073 K was carried out at 293–473 K using a fixed-bed flow reactor. Products in the alkylation at 293 K were isopropylbenzene, m- and p-diisopropylbenzenes, 1,3,5-tri-isopropylbenzene and 1,2,4,5-tetraisopropylbenzene. No chlorine-substituted benzenes were detected. The conversion of 2-chloropropane to the substituted benzenes was about 14 times that on the alumina dehydrated in vacuo, and the 1,3,5-triisopropylbenzene produced was about 70% of the liquid products. An increase in benzene-to-chloropropane ratio retarded the lowering of conversion with reaction time and increased the yield of isopropylbenzene. The reactivity of 1-chloropropane was about one-tenth of that of 2-chloropropane, but the isopropylbenzene content was greater. At the reaction temperature of 333 K, dehydrochlorination of 2-chloropropane began to take place, and above 373 K this was a main reaction. Also, the chlorination temperature dependence of the catalytic activities for alkylation and dehydrochlorination was similar to that for Lewis acidity with a maximum in the range 973 to 1073 K. The alkylation was explained to proceed through a Friedel—Crafts-type intermediate.