Para-selective chlorination of cumene with sulfuryl chloride over zeolite catalysts

Abstract

The liquid phase chlorination of cumene has been investigated in the presence of a series of zeolite catalysts and also the conventional catalyst AlCl 3 at 333 K under atmospheric pressure with sulfuryl chloride (SO 2Cl 2) as the chlorinating agent. Zeolite K-L catalyzes the chlorination of cumene selectively to 4-chlorocumene (4-ClCm) and is superior to other zeolite catalysts and AlCl 3 in terms of selectivity. Zeolite K-X and the uncatalyzed reaction produce mainly the side-chain chlorinated product, α-chlorocumene (α-ClCm) with much less activity, whereas AlCl 3 gives higher amounts of consecutive products. The effect of reaction time, solvent, catalyst (K-L) concentration, cumene:SO 2Cl 2 ratio, HCl treated K-L and recycle of K-L on the conversion of cumene and selectivity for 4-ClCm have been examined. The activity and selectivity of zeolite K-L depend on the reaction conditions and on the solvent used in the reaction. 1,2-Dichloroethane (EDC) is found to be the best solvent and gives the highest selectivity for 4-ClCm:2-chlorocumene (2-ClCm) = 33.0 at 353 K in the chlorination of cumene with K-L. Further, the use of EDC as solvent prevents the formation of the side-chain as well as consecutive products. With an increase in the reaction temperature, the rate of cumene conversion as well as the selectivity for 4-ClCm have been found to increase. Also, increase in the concentration of K-L to 25 g/mol of cumene in the presence of EDC gives the highest 4-ClCm:2-ClCm ratio of 38.6 at 353 K. The HCl-treated zeolite K-L shows lower activity and selectivity than parent K-L, due to increased SiO 2:Al 2O 3 ratio as well as (to some extent) decreased crystallinity of HCl-treated zeolite K-L. The conversion of cumene is found to increase with a decrease in the cumene:SO 2Cl 2 molar ratio and consequently, in an increase in the concentration of SO 2Cl 2. The catalyst is recycled two times with a progressive decline in its activity. A few reactions of cumene chlorination with molecular chlorine are also studied with zeolite K-L. In this case, a combination of zeolite K-L, chloroacetic acid and EDC serves as the best catalyst, giving highly selective para-chlorination of cumene at 353 K under atmospheric pressure. The reaction pathway involves the formation of molecular chlorine by the decomposition of SO 2Cl 2 at the reaction temperature. The catalyst then polarizes the chlorine molecule to the electrophile (Cl +), which interacts with cumene molecule in an electrophilic substitution reaction, giving ring-chlorinated cumenes.