Following solid-acid-catalyzed reactions by MAS NMR spectroscopy in liquid phase--zeolite-catalyzed conversion of cyclohexanol in water.

Abstract

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 (13) C spectra show that dehydration of 1-(13) C-cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the (13) C label. A simplified kinetic model shows the E1-type elimination fully accounts for the initial rates of 1-(13) C-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.

• Authors: Aleksei Vjunov, Mary Y Hu, Ju Feng, Donald M Camaioni, Donghai Mei, Jian Z Hu, Chen Zhao, Johannes A Lercher
• Journal: Angewandte Chemie (International ed. in English) (Angew Chem Int Ed Engl) Vol. 53 Issue 2 Pg. 479-82 (Jan 07 2014) ISSN: 1521-3773 [Electronic] Germany
• PMID: 24282024 (Publication Type: Journal Article)
• Copyright: Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.