A process for producing sec-butylbenzene comprises feeding reactants comprising benzene and a C4 olefin to a distillation column reactor having a first reaction zone containing an alkylation catalyst and a second distillation zone, which is located below said first reaction zone and which is substantially free of alkylation catalyst, wherein the ratio of the number of distillation stages in said first reaction zone to the number of distillation stages in said second distillation zone is less than 1:1. Concurrently in the distillation reactor, the reactants are contacted with the alkylation catalyst in the first reaction zone under conditions such that the C4 olefin reacts with the benzene to produce sec-butylbenzene and the sec-butylbenzene is fractioned from the unreacted C4 olefin. The sec-butylbenzene thereby passes as a liquid phase stream from the first reaction zone to the second distillation zone and the liquid phase steam is withdrawn from the distillation column reactor as bottoms.