Organic reactions in a clay microenvironment

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Abstract
Although natural Na-bentonite has little catalytic activity, various cation-exchanged bentonites have proved to be effective catalysts for a wide variety of organic reactions. In the presence of these catalysts alkenes can be induced to add (a) water, to yield branched-chain symmetrical ethers; (b) alcohols, to give a variety of ethers; (c) thiols, to yield thio-ethers; (d) carboxylic acids, to give esters. The number of products obtained in each reaction depends on the ease of rearrangement of the carbocation intermediates. High yields are obtained where a single carbocation intermediate is formed, A variety of elimination reactions is also catalysed by these sheet silicates. Water is eliminated from alcohols to produce ethers, ammonia is eliminated from amines to make secondary amines, and hydrogen sulphide is eliminated from thiols to give dialkyl sulphides. In most cases the ion-exchanged bentonites react as acidic heterogeneous catalysts.