Selective chlorination of 4-chlorotoluene to 2,4-dichlorotoluene over zeolite catalysts

The performance of various zeolites in the liquid phase chlorination of 4-chlorotoluene (4-CT) with gaseous chlorine at a moderate temperature and normal pressure has been examined. A comparison under the same conditions with Lewis acid catalyst FeCl3, is also carried out. It is found that zeolite K-L exhibits higher selectivity for 2,4-dichlorotoluene (2,4-DCT/3,4-DCT = 3.54) compared to the other zeolites studied and also FeCl3 catalyst (2,4-DCT/3,4-DCT = 3.18), while the rate of 4-CT conversion (75.8 mmol g(-1) h(-1)) is found to be comparable on K-L and FeCl3 catalysts. The highest rate of 4-CT conversion, among the catalysts studied is obtained over K-beta (101.4 mmol g(-1) h(-1)). FeCl3 catalyst produces higher amounts of tri- and tetra-substituted products due to its non-shape-selective character. Mainly the side-chain chlorinated product (alpha,4-dichlorotoluene) is obtained over K-X, amorphous SiO2 and in the absence of catalyst. Solvents influence the rate of 4-CT conversion as well as the 2,4-DCT/3,4-DCT isomer ratio. 1,2-dichloroethane appears to be the best solvent in enhancing the 2,4-DCT/3,4-DCT isomer ratio when the reaction temperature is raised from 313 to 353 K.