Reactions of the helium tritiide ion with liquid arenes

Abstract

The reactivity of the HeT⁺ ion from the β-decay of molecular tritium to benzene and toluene has been investigated in the liquid phase. It is suggested that the tritiodeprotonation occurs via a mechanism based upon the exothermic triton transfer from HeT⁺ to the arene, leading to the formation of an excited arylium ion followed by its collisional stabilization and by a thermoneutral proton transfer to another molecule of substrate. The attack of the HeT⁺ reagent is characterized by the complete lack of substrate selectivity, as expected for an extremely reactive free cation carrying a net positive charge of unity. On the other hand, despite its extreme electrophilic character, the reagent retains a remarkable positional selectivity. The implications of these findings are discussed, and the behaviour of the HeT⁺ ion is compared with that of poorly solvated ‘ionic’ reagents, obtained with conventional techniques, towards the same substrates in non-polar solvents.