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Applied Catalysis A: General, Vol.228, No.1-2, 1-13, 2002
Para-selective chlorination of cumene with sulfuryl chloride over zeolite catalysts
The liquid phase chlorination of cumene has been investigated in the presence of a series of zeolite catalysts and also the conventional catalyst AlCl3 at 333 K under atmospheric pressure with sulfuryl chloride (SO2Cl2) 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 AlCl3 in terms of selectivity. Zeolite K-X and the uncatalyzed reaction produce mainly the side-chain chlorinated product, alpha-chlorocumene (alpha-ClCm) with much less activity, whereas AlCl3 gives higher amounts of consecutive products. The effect of reaction time, solvent, catalyst (K-L) concentration, cumene:SO2Cl2 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 SiO2:Al2O3 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:SO2Cl2 molar ratio and consequently, in an increase in the concentration of SO2Cl2. 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 SO2Cl2 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.