Mechanism of hydration and dehydration reactions in presence of zinc halides

Abstract

1. It is shown that, in the hydration of olefins and dehydration of alcohols in presence of zinc halides as catalysts, intermediate complexes are formed which later decompose, in a manner dependent on conditions, with formation of the final reaction products. 2. Both in the reaction of zinc halides with alcohols and in the reaction between hydroxohalozinc acids and the unsaturated hydrocarbons corresponding to these alcohols, the same intermediate complexes are formed. This indicates the existence of a state of equilibrium between the reactions of hydration of olefins and dehydration of alcohols. On the basis of these data and of a detailed investigation of the composition of complexes formed by zinc halides with alcohols and unsaturated hydrocarbons, a possible mechanism is proposed for hydration and dehydration reactions in presence of zinc halides as catalysts. 3. Comparison between hydration and dehydration reactions catalyzed by zinc halides, on the one hand, and by mineral acids, on the other, shows that they are very similar in mechanism. 4. On the basis of theoretical considerations and of a study of the properties of the intermediate zinc halide compounds, a possible structure is proposed for the intermediate complexes.