Trifluoromethanesulphonic acid as a catalyst for the ethylation of benzene

Abstract

At room temperature and a pressure of ethene of 1 atm, anhydrous trifluoromethanesulphonic (triflic) acid is a more effective catalyst for the ethylation of benzene than AlCl₃, FSO₃H, and anhydrous H₂SO₄. It has an activity comparable to that found for a 1 : 1 mixture of FSO₃H–SbF₅, and under the most favourable conditions the yield of ethylbenzene is ca. 38% based on the amount of benzene reacted. Although the initial rate of ethylation is rapid, the reaction effectively ceases after 30–60 min depending on the reaction conditions. The reason for this has mainly been shown to be strong complexation of the triflic acid to polyethylbenzene derivatives in the catalyst layer, but also, in part, to the competing formation of ethyl triflate, which is inactive as an ethylating agent under the conditions used.