Deuteration of hexane by [formula omitted] in supercritical deuterium oxide

Abstract

Hexane is shown to undergo isotopic hydrogen exchange with 2 HCl in supercritical deuterium oxide at 380 and 400°C. The deuteration rate follows pseudo first order kinetics at both temperatures with the methylene reaction rate being about 1.6 times that of methyl. The isotopic exchange reaction is analyzed as a two step acid/base mechanism, with hexane acting as a base analogous to its behavior in `magic acid' solution. Measured K b's for the methyl group are 3.5×10 −28 and 9.2×10 −28, while the methylene groups have K b's of 6.0×10 −28 and 1.5×10 −27 at 380 and 400°C, respectively. No evidence is seen for hydride abstraction, such as formation of carbocation rearrangement species or hydrogen gas evolution as in `magic acid'. Hydride abstraction to form carbocations either does not occur or occurs at a rate too slow to be observed in the time scale of the experiments reported here.