The catalytic performance of trifluoromethanesulphonic acid (triflic acid) has been investigated for synthesis of ethylbenzene (EB) by transalkylation of o-diethylbenzene (DEB) with benzene (B). Different mole ratios of benzene to the isomer (1:1, 3:1 and 6:1) were used at atmospheric pressure and low temperatures (15-35 degrees C). Ethylbenzene was the main product of the transalkylation. From isomerization reactions, the products were o-diethylbenzene isomers (meta- and para-), and from disproportionation reactions, 1,3,5-triethylbenzene was also obtained. In the case of 1: 1 mole ratio of benzene to the isomer, yield of ethylbenzene of 49 mol% was obtained after 6 h of reaction at 35 degrees C. This decreased, at the same temperature, to 25 and 8 mol% for 3:1 and 6:1 mole ratios, respectively. A decrease in the temperature to 25 and 15 degrees C (with 1: 1 mole ratio), caused the yield of ethylbenzene to decrease to 43 and 32 mol%, respectively. Similar trends were observed with 3:1 and 6:1 ratios. The conversion of o-diethylbenzene to ethylbenzene and ethylated benzenes appeared to depend strongly on mole ratio of benzene/diethylbenzene at a given temperature. The study has shown that the triflic acid is active as a catalyst for the reaction. It exhibited high yield of ethylbenzene from o-diethylbenzene at low temperatures and atmospheric pressure. (c) 2004 Published by Elsevier B.V.