Alkylation of benzene by alkyl cations. Stability of the tert-butyl benzenium ion

Article abstract of DOI:10.1139/v82-331

The kinetics and eqilibria of the gas phase reaction <1> tert-C4H9⁺ + C6H6 = tert-C4H9C6H6⁺ 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 ΔH₁⁰ = -22+/-2 kcal mol^-1 and ΔS₁⁰ = -49+/-5 cal K^-1 mol^-1.The rate constants at 305 K were k_1f = 1.5*10^-28 molecules^-2 cm⁶ s^-1 and k_1r = 2.9*10^-19 molecules^-1 cm³ s^-1. tert-C4H9C6H6⁺ dissociates easily via <1r> not only because of the low dissociation energy (-ΔH₁⁰) but also because of the unusually favorable entropy (-ΔS₁⁰).The occurence of transalkylation reactions: tert-C4H9C6H6⁺ + alkylbenzene = tert-C4H9 alkylbenzene⁺ + benzene, was discovered in the present work.