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

• Published in: Angewandte Chemie 2014-01, Vol.126 (4), p.1149-1152
• Main Authors: Nava, Matthew, Stoyanova, Irina V., Cummings, Steven, Stoyanov, Evgenii S., Reed, Christopher A.
• Format: Article
• Language: eng ; ger
• Subjects: Brønsted-Säuren; Carbokationen; Carborane; Chemistry; Kohlenwasserstoffe
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201308586

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(CHB11F11) is that acid. It is an extremely moisture‐sensitive solid, prepared by treatment of anhydrous HCl with [Et3SiHSiEt3][CHB11F11]. It adds H2O to form [H3O][CHB11F11] and benzene to form the benzenium ion salt [C6H7][CHB11F11]. It reacts with butane to form a crystalline tBu+ 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 H2. By protonating alkanes at room temperature, the reactivity of H(CHB11F11) opens up new opportunities for the easier study of acid‐catalyzed hydrocarbon reforming. Der Protonator: Das fluorierte Carboran H(CHB11F11) – die stärkste bislang bekannte Brønsted‐Säure – kann Alkane bei Raumtemperatur protonieren. Stabile Salze von Carbokationen konnten isoliert werden. Die neuartige Supersäure eröffnet neue Perspektiven auf dem Gebiet der Kohlenwasserstoffreformierung.