The Strongest Brønsted Acid: Protonation of Alkanes by H(CHB₁₁F₁₁) at Room Temperature

Abstract

Abstract What is the strongest acid? Can a simple Brønsted acid be prepared that can protonate an alkane at room temperature? Can that acid be free of the complicating effects of added Lewis acids that are typical of common, difficult‐to‐handle superacid mixtures? The carborane superacid H(CHB 11 F 11 ) is that acid. It is an extremely moisture‐sensitive solid, prepared by treatment of anhydrous HCl with [Et 3 SiHSiEt 3 ][CHB 11 F 11 ]. It adds H 2 O to form [H 3 O][CHB 11 F 11 ] and benzene to form the benzenium ion salt [C 6 H 7 ][CHB 11 F 11 ]. It reacts with butane to form a crystalline t Bu + salt and with n ‐hexane to form an isolable hexyl carbocation salt. Carbocations, which are thus no longer transient intermediates, react with NaH either by hydride addition to re‐form an alkane or by deprotonation to form an alkene and H 2 . By protonating alkanes at room temperature, the reactivity of H(CHB 11 F 11 ) opens up new opportunities for the easier study of acid‐catalyzed hydrocarbon reforming.