Abstract
The etherification reaction between benzoin derivatives and alcohols catalyzed by
iron(III) proceeds in moderate to good yields. Other metal complexes showed either
low reactivity or low chemoselectivity where oxidation of benzoin to benzil was a
competing reaction. The iron source operated as a catalyst where 5 mol% of iron(III)
generate the 2-alkoxy-1,2-diphenylethan-1-one in 50% yield. With an optimum of 25
mol% of catalyst, the desired ether was obtained in 85% yield. The etherification
of benzoin and an alcohol proceed to generate the desired product in polar solvents
such as 1,2-dichloroethane, whereas less polar solvents promote the competing oxidation
to generate the benzil; polar coordinating solvents such as tetrahydrofuran inhibited
the reaction. The efficiency of the reaction is found to be dependent on nucleophile
where an optimum of 30 equivalents of alcohol was observed. With electron-donating
substituents on the aromatic ring, the etherification was followed by oxidation to
generate the benzil. Moderate yields of etherification product were obtained by monitoring
the reaction progress with electron-rich substrates and quenching the reaction after
two hours.
Key words
iron catalysis - Lewis acids - substitution - ethers - alcohols
