Transition states of catalytic dehydration and dehydrogenation of alcohols

Abstract

Transition states accounting for characteristics of the dehydration of alcohols, e.g. cis preference, anti elimination, are derived from experimental details, in particular, product distribution with deuterated and non-deuterated reactants. The coordination chemical approach to catalysis is used and attention is mainly paid to the atom-to-atom bonding between catalyst and reactant. Basicity of the catalyst turns out to be more important for the transition state and, hence, the product formed, than steric factors. The important role of basic sites, which are usually less taken into account, for mechanism and selectivity is pointed out. The considerations refer mainly to the E2 mechanism. Basicity of catalysts, in addition to matching of distances, is shown also to be the determining factor, for the selectivity for dehydrogenation, which is always associated with an E1cB mechanism for dehydration.