Mechanism of isotopic exchange

Cole DR, Chakraborty S (2001) Rates and mechanisms of isotopic exchange. Rev Mineral Geochem 43 83-223... 

Feng X. and Savin S.M. (1993) Oxygen isotope studies of zeolites stiblite, analcime, heulandite and clinoptilolite, II kinetics and mechanism of isotopic exchange between zeolites and water vapor. Geochim. Cosmochim. Acta 57, 4219-4238. 

In the first studies of isotope exchange of the haloforms, general base catalysis could not be clearly observed [164]. In more recent studies of the detritiation of chloroform in aqueous morpholine and piperidine buffers, general base catalysis could not be detected and the reaction was dominated by hydroxide ion catalysis [114]. In this latter study it was assumed that the mechanism of isotope exchange consisted of a slow triton transfer to base (99), viz. 

Adsorption measurements, therefore, are still not very fruitful for the study of the mechanism of isotopic exchange of oxide. On the contrary, the measurement of the isotopic exchange rate in molecular oxygen is the only reliable method for estimation of the rate of adsorption (or desorption) of oxygen in the neighbourhood of adsorption equilibrium. 

Two mechanisms of isotopic exchange in alcohols can he considered, corresponding to the SN1 and SN2 mechanisms of nucleophilic substitution. Water is the nucleophile in this case, attacking a saturated carbon atom. In all the studies reported so far, exchange occurs only in acid solution and it has always been assumed that the conjugate acid of the alcohol is the reacting species. 

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