Hydration of alkene oxides to glycols

In homogeneous liquid media, the hydration is catalysed by acids or bases. With solid catalysts, the reaction may be performed with both reactants either in the vapour [285,307—311] or in the liquid [312—314] phase. In the former case, temperatures of about 120—250°C, and in the latter case of about 25—90°C, were used. The reaction can also be conducted under conditions which establish a heterogenous system of vapour and liquid phases [308]. 

Formal kinetic investigations (performed only with acidic ion exchange catalysts) revealed, in most cases, the first-order rate law with respect to the alkene oxide [285,310,312] or that reaction order was assumed [309,311]. Strong influence of mass transport (mainly internal diffusion in the polymer mass) was indicated in several cases [285,309, 310,312,314]. The first-order kinetics with respect to alkene oxide is in agreement with the mechanism proposed for the same reaction in homogeneous acidic medium [309,315—317], viz. 

With an inorganic catalyst (Ag20/Al203 [307]) a simple surface process is assumed for the vapour phase hydration water adsorbed on the surface of silver oxide reacts with gaseous ethylene oxide to form adsorbed glycol which is then desorbed this is obviously an oversimplification of the actual mechanism. 

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