Studies of Alcohol Dehydration on Zeolites

Mechanistic Studies of Alcohol Dehydration on Zeolites. - Gentry and Rudham and Jacobs et al have proposed mechanisms for the dehydration of propan-2-ol and butan-2-ol on X-zeolites. Both groups of workers are in basic agreement about the mechanism, which involves the formation of oxonium and carbonium ions. The formation of olefins from the above alcohols appeared to occur via an El -like mechanism and this was supported very strongly by the behaviour of butan-2-ol, which gave a primary isotope effect, but an absence of one for C 3- H, rules out the E2 mechanism. 

Gentry and Rudham proposed a mechanism involving oxonium ions, which led to carbonium ion formation and thence to the olefin. In the case of ether formation, a reaction between two positively changed ions, i.e. one carbonium and one oxonium ion, was proposed. Jacobs et al. disagreed with their mechanism and proposed that the ether is formed by a parallel path to olefin formation via a common intermediate. Indeed, in a later study, Rudham and StockweU, using Y-zeolites suggested a mechanism, in which a single site only is involved for ether formation and differs only in small detail from that of Jacobs et al. 

Since the Oij binding energy of zeolites is less than that of Si02-Al203, the 

In view of the means available to vary acidity and basicity of zeolites, studies of mechanistic detail using model alcohols might be very rewarding. 

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