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

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 alcohol to 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%.

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► An environmentally benign catalytic system for oxidation.
► Selective oxidation of alcohols to aldehydes achieved with a biphasic ionic liquid medium.
► Short reaction time at low temperature.
► Easy separation of products and convenient recycling of the medium.