The liquid phase chlorination of diphenylmethane (DPM) to 4,4'-dichlorodiphenylmethane (4,4'-DCDPM) is investigated at 333 K, under atmospheric pressure over a number of zeolite catalysts using sulfuryl chloride (SO2Cl2) as the chlorinating agent. The results obtained are compared with those over the conventional Lewis acid catalyst, AlCl3 as A ell as without any catalyst. Zeolite K-L is found to be highly active and selective catalyst for the conversion of DPM to 4,4'-DCDPM. The conversion of DPM, rate of DPM conversion and the selectivity (4,4'-DCDPM/2,4'-DCDPM isomer ratio) over zeolite K-L after 1 h of reaction time are found to be 96.8 wt.%, 19.1 mmol g(-1) h(-1) and 7.4, respectively. The influence of solvent, catalyst concentration, reaction temperature, DPM/SO2Cl2, molar ratio. recycle of zeolite K-L, etc. are also examined. 1,2-Dichloroethane is the best solvent and gives the highest selectivity for 4.4'-DCDPM (4.4'-DCDPM2.4'-DCDPM isomer ratio = 9.7) with zeolite K-L at 353 K after I h of reaction time. The formation of 4,4'-DCDPM is favoured by increase in catalyst concentration, reaction temperature and higher concentration of SO2Cl2, (lower DPM/SO2Cl2 molar ratio). In all these cases, the yield of 4,4'-DCDPM increases with a decrease in the yield of 4-CDPM which suggests that the formation of 4,4'-DCDPM takes place by the consecutive reaction of 4-CDPM. Higher SiO2/Al2O3 ratio (obtained by HCl treatment) of zeolite K-L decreases the conversion of DPM. A noticeable decrease in the activity and selectivity of zeolite K-L is observed or recycling, probably due to reduced crystallinity as well as extraction of small amounts of Al+3 and K+ ions by the HCl, generated in the reaction. Mechanistically, SO2Cl2, is first decomposed into SO2 and Cl-2 the latter being polarized by the zeolite catalyst to an clectrophile (Cl+) which then attacks the DPM and subsequently produce the monochlorodipherylmethane (MCDPM). The MCDPM further is attacked by the electrophile (Cl+) and result in the formation of DCDPM. (C) 2002 Elsevier Science B.V. All rights reserved.