Natural kaolinitic clay: A remarkable catalyst for highly regioselective chlorination of arenes with Cl2 or SO2Cl2

Introduction of chlorine into aromatic rings by electrophilic substitution is an important synthetic transformation because chlorinated hydrocarbons are recognized as versatile starting materials and additives in th e p rod uctio n o f h igh qu ality in sectic ides, fungicides, herbicides, dyes, pharmaceuticals 1 Moreover, they can serve as precursors for numerous functionalities, such as phenols, aromatic ethers and thioethers, amines, aryl hydrazines, benzonitriles, benzaldehyd es , fluoro aromatics and arom atic hydrocarbons2. In general, chlorination of aromatic ring is achieved either by using chlorine or SO2Cl2 as chlorine source in presence of Lewis acid catalysts such as Al3+, Fe3+, Sn4+ or Zn2+ chlorides, acetic acid .3 But use of homogenous catalyst has the drawback such as poor regioselectivity, difficulty in separation of the catalyst from the reaction mixture, generation of toxic waste . Secondly, use of mineral acids and metallic halides create work-up and effluent problem in the industrial scale production of these compounds. Use of solid acid is an easy, safe and economical process, which does not create any environmental problem. Several efforts have been made for the replacement of these homogeneous catalysts with solid acids such as zeolites for the chlorination of arene4. Although -selectivity was achieved using zeolite4 because of it’s shape selective nature, there is not such report for -selective chlorination. Sheldon reported a highly regioselective chlorination of phenol with SO2Cl2-amine systems in homogeneous phase5. In recent years, acid catalysis of organic transformations by clay aluminosilicates6 is an area of considerable potential and interest due to the ease of handling and w ork-up, absence o f toxicity and corrosion and low cost of clays. Due to their Br nsted and Lewis acidities, clays function as efficient catalysts for a variety of impor tant transformations7. An interesting feature of clay catalyst is that it gives unexpected -selective products in a few cases, which is very specific for a particular combination of substrates8. This peculiar property is sometimes very much useful for the synthesis of some important substituted compounds. Herein is reported the use of natural kaolinitic clay for the chlorination of arenes with substantial degree of regioselectivity with Cl2 or SO2Cl2 as the chlorinating agent ( ). The k ao lin itic clay w as pro cu red f ro m th e Padappakara mine of Quilon District, Kerala, India and