Following Solid-Acid-Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase-Zeolite-Catalyzed Conversion of Cyclohexanol in Water

A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid–liquid–gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The 13C spectra show that dehydra...

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Bibliographic Details
Published in:Angewandte Chemie 2014-01, Vol.126 (2), p.489-492
Main Authors: Vjunov, Aleksei, Hu, Mary Y., Feng, Ju, Camaioni, Donald M., Mei, Donghai, Hu, Jian Z., Zhao, Chen, Lercher, Johannes A.
Format: Article
Language:eng ; ger
Subjects:
Alkoholdehydratisierung
Catalysts
Cations
Chemistry
Dehydration
Ethers
Heterogene Katalyse
Liquids
NMR-Spektroskopie
Reaction kinetics
Reaktionsmechanismen
Rotors
Spinning
Zeolithe
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Summary:A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid–liquid–gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The 13C spectra show that dehydration of 1‐13C‐cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the 13C label. A simplified kinetic model shows the E1‐type elimination fully accounts for the initial rates of 1‐13C‐cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2‐hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl‐1‐cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100‐fold faster per proton. Heiße Analyse: Die katalytische Umsetzung von Cyclohexanol mit dem Zeolith HBEA in heißem flüssigem Wasser führt zu Dehydratations‐ und Alkylierungsprodukten. Mithilfe eines Mikroautoklaven, der für die Aufnahme von NMR‐Spektren mit Probenrotation um den magischen Winkel (magic angle spinning=MAS) geeignet ist, wurden Kenntnisse über den mechanistischen Verlauf der Reaktion unter den gewählten experimentellen Bedingungen gewonnen.
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.201306673