The synthesis valuable para-dialkylbenzenes over shape selective zeolites is of immense industrial importance. The shape selectivity was achieved by regulating the pore mouth opening of ZSM-5 zeolites by employing chemical vapour deposition (CVD) of silica. Two probe molecules of different kinetic diameter were used to follow the extent of pore mouth regulation. The post synthesis modification resulted in obtaining para-substituted dialkylbenzenes of high purity by alkylation of monoalkylbenzenes with C-1-C-3 alcohols. Similarly, para-substituted dialkylbenzene have been synthesised over pore size regulated zeolites by toluene disproportionation and paraffin aromatisation reactions. The above technique of enhancing para-selectivity has been successfully employed to develop an ecofriendly process for the manufacture of value added chemical para-diethylbenzene by ethylation of ethylbenzene. The paper highlights some of the unique advantages of pore size regulated zeolites for the synthesis of para-dialkylbenzenes over the conventional acid catalysed reactions. C 2002 Elsevier Science B.V. All rights reserved.