The kinetics of hydrogen isotope exchange reactions. Part XIV. Acid-catalysed tritium exchange and its relationship to the dehydration of t-butyl alcohol

Abstract

The rate of hydrogen exchange between tritium-containing aqueous perchloric acid and the C–H bond of dissolved t-butyl alcohol has been measured at 25° as a function of acid concentration. The logarithm of the rate constant is a linear function of H₀ with slope –1·35. On the assumption that exchange takes place by dehydration to isobutene followed by re-addition of labelled water, the results are used to obtain the rate constant for dehydration of t-butyl alcohol in 0·5M-perchloric acid. The value found agrees with one calculated by combining the previously determined rate constant for hydration of isobutene with the equilibrium constant for the hydration reaction evaluated from thermodynamic data. This agreement supports the view that the route via olefin is the most significant mechanism of hydrogen exchange of t-butyl alcohol in moderately dilute aqueous acid at 25°.