Alkylation of benzene by alkyl cations. Stability of the <i>tert</i>-butyl benzenium ion

Abstract

The kinetics and equilibria of the gas phase reaction [1] tert-C 4 H 9 + + C 6 H 6 = tert-C 4 H 9 C 6 H 6 + were studied with a high ion source pressure pulsed electron beam mass spectrometer. Equilibria [1] could be observed in the temperature range 285–325 K. van't Hoff plots of the equilibrium constants led to [Formula: see text] and [Formula: see text]. The rate constants at 305 K were k lf = 1.5 × 10 −28 molecules −2 cm 6 s −1 and k lr = 2.9 × 10 −1 molecules −1 cm 3 s −1 . tert-C 4 H 9 C 6 H 6 + dissociates easily via [lr] not only because of the low dissociation energy [Formula: see text] but also because of the unusually favorable entropy [Formula: see text]. The occurrence of transalkylation reactions: tert-C 4 H 9 C 6 H 6 + + alkylbenzene = tert-C 4 H 9 alkylbenzene + + benzene, was discovered in the present work.