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Unusual Rate Acceleration in Brønsted Acid Catalyzed Dehydration Reactions: Local Hydrophobic Environment in Aggregated N ‐(2,6‐diphenylphenyl)‐ N ‐mesitylammonium Pentafluorobenzenesulfonates
Author(s) -
Sakakura Akira,
Watanabe Hitoshi,
Nakagawa Shoko,
Ishihara Kazuaki
Publication year - 2007
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200600380
Subject(s) - oxonium ion , catalysis , chemistry , dehydration , intramolecular force , intermolecular force , hydrogen bond , crystallization , brønsted–lowry acid–base theory , medicinal chemistry , condensation , ion , organic chemistry , molecule , biochemistry , physics , thermodynamics
Bulky diarylammonium pentafluorobenzenesulfonates effectively promote dehydration reactions, such as condensation reactions to give esters and the dehydrative cyclization of 1,3,5‐triketones. In particular, N ‐(2,6‐diphenylphenyl)‐ N ‐mesitylammonium pentafluorobenzenesulfonate shows much higher catalytic activity than C 6 F 5 SO 3 H under reaction conditions without the removal of generated water, even though the former is a weaker acid. Its crystallization gives an aggregated cyclic ion pair, which is composed of two diarylammonium cations, four pentafluorobenzenesulfonate anions, and two oxonium cations. This ion pair is strongly stabilized by four intermolecular and two intramolecular π–π attractive interactions and 10 hydrogen bonds. The extremely high catalytic activity of N ‐(2,6‐diphenylphenyl)‐ N ‐mesitylammonium pentafluorobenzenesulfonate in the dehydration reactions may be ascribed to the local hydrophobic environment of the tightly aggregated ammonium salts.