Selectivity Differences of Hexene Isomers in the Alkylation of Benzene over Solid Phosphoric Acid

Alkylation of benzene with 1-hexene, 2-methylpentenes, 3-methylpentenes, and 2,3-dimethyl-2-butene has been investigated over a solid phosphoric acid (SPA) catalyst at 220 °C. It was found that on SPA linear olefins preferably alkylated, rather than dimerized, as opposed to branched olefins that preferably dimerized. The initial selectivity ratios of dimerization to alkylation for the hexene isomers are 0.16 (n-hexenes), 12 (3-methylpentenes), 21 (2-methylpentenes), and 33 (2,3-dimethylbutenes). SPA did not readily form heavy oligomers or dialkylated benzenes and had a high propensity for the skeletal isomerization of hexenes. The alkylbenzene product selectivities could not be used to confirm that benzene alkylation always proceeded through a protonated cyclopropane (PCP) intermediate over SPA, as was found during SPA catalyzed alkylation of benzene with 1-pentene.