Controlling the selectivity of the manganese/bicarbonate/hydrogen peroxide catalytic system by a biphasic pyrrolidinium ionic liquid/n-heptane medium

Authors: Wing-Leung Wong, Kam-Piu Ho, Lawrence Yoon Suk Lee, Ming-Him So, Tak Hang Chan, Kwok-Yin Wong

Abstract:
The Mn²⁺/HCO₃ −/H₂O₂ catalytic system exhibits excellent aldehyde selectivity in the oxidation of various benzylic and allyic alcohols under mild conditions and short reaction time when the reactions are carried out in a biphasic dicationic pyrrolidinium ionic liquid/n-heptane medium. The dicationic pyrrolidinium ionic liquid shows differential solubility towards alcohols and their aldehydes whereas the immiscible n-heptane instantaneously extracted and separated aldehydes from the reaction phase. This design of biphasic ionic liquid/n-heptane catalytic system prevents the over-oxidation of aldehydes to carboxylic acids effectively. Separation and recycling can also be easily done by decantation of the n-heptane layer after reaction. With the biphasic system, high conversion of benzyl alcoholto benzaldehyde was achieved with very low loadings of H₂O₂ and Mn(OAc)₂ catalyst at room temperature and within short reaction time. Throughout 10 reaction cycles, a total turnover number (TON) of 37,600 was achieved and excellent catalytic reactivity and selectivity were maintained with an average yield of 94%. 

Keywords:
Ionic liquid
Manganese catalyst
Hydrogen peroxide
Oxidation
Green chemistry

Published in: Applied catalysis A: General  (Volume 453, Pages 1-402, 26 February 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

Controlling the selectivity of the manganese/bicarbonate/hydrogen peroxide catalytic system by a biphasic pyrrolidinium ionic liquid/n-heptane medium

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