Catalytic Dehydration of Alcohols. Kinetic Isotope Effect for the Dehydration of t-Butanol

The kinetic isotope effects (KIE) for the conversion of an equimolar mixture of C4D9OH and C4H9OH and for the KIE for the intermolecular elimination of water from (CD3)2CH3COH for an alumina-catalyzed reaction were the same, 2.1–2.3. These results eliminate a carbocation intermediate for the dehydration of even a tertiary alcohol. Thus, for an alumina catalyst alcohol dehydration occurs by a concerted elimination mechanism. H/D exchange occurs to different extents prior to or during elimination for zirconia, thoria and magnesia catalysts; however, the data are consistent with a concerted elimination mechanism in combination with H/D exchange.