Organic reactions catalysed by sheet silicates: ether formation by the intermolecular dehydration of alcohols and by addition of alcohols to alkenes

Abstract

Ion-exchanged montmorillonites can be used as heterogeneous catalysts for the dehydration of liquid alcohols in pressure vessels at 200 °C. In contrast to the situation with homogeneous, aqueous acid catalysts, primary alcohols undergo preferential intermolecular dehydration to give good yields of di(alk-1-yl) ethers with these sheet silicate catalysts, whereas secondary and tertiary alcohols undergo the expected facile intramolecular dehydration to the corresponding stable alkenes. With the acid clay catalysts, primary diols give either oligomeric or cyclic ether products by intermolecular dehydration, whereas benzyl alcohol undergoes intermolecular dehydration to produce a polymeric material, poly(phenylene methylene), in the presence of ion-exchanged montmorillonites. Primary alcohols can be induced to add onto highly substituted alkenes to produce mixed primary/tertiary ethers in excellent yields. Less highly substituted alkenes give much lower yields of mixed ethers. In general, these catalysts are more selective than concentrated mineral acids and have the distinct advantage of being much easier to separate from the products.