Fétizon oxidation

Fétizon oxidation is the oxidation of primary and secondary alcohols utilizing the compound silver(I) carbonate absorbed onto the surface of celite also known as Fétizon's reagent first employed by Marcel Fétizon in 1968. It is a mild reagent, suitable for both acid and base sensitive compounds. Its great reactivity with lactols makes the Fétizon oxidation a useful method to obtain lactones from a diol. The reaction is inhibited significantly by polar groups within the reaction system as well as steric hindrance of the α-hydrogen of the alcohol.

Fétizon's reagent is typically prepared by adding silver nitrate to an aqueous solution of a carbonate, such as sodium carbonate or potassium bicarbonate, while being vigorously stirred in the presence of purified celite.

A proposed mechanism for the oxidation of an alcohol by Fétizon's reagent involves single electron oxidation of both the alcoholic oxygen and the hydrogen alpha to the alcohol by two atoms of silver(I) within the celite surface. The carbonate ion then proceeds to deprotonate the resulting carbonyl generating bicarbonate which is further protonated by the additionally generated hydrogen cation to cause elimination of water and generation of carbon dioxide.

The rate limiting step of this reaction is proposed to be the initial association of the alcohol to the silver ions. As a result, the presence of even weakly associating ligands to the silver can inhibit the reaction greatly. As a result, even slightly polar solvents of any variety, such as ethyl acetate or methyl ethyl ketone, are avoided when using this reagent as they competitively associate with the reagent. Additional polar functionalities of the reactant should also be avoided whenever possible as even the presence of an alkene can sometimes reduce the reactivity of a substrate 50 fold. Commonly employed solvents such as benzene and xylene are extremely non-polar and further acceleration of the reaction can be achieved through the use of the more non-polar heptane. The solvent is also typically refluxed to drive the reaction with heat and remove the water generated by the reaction through azeotropic distillation. Steric hindrance of the hydrogen alpha to the alcohol is a major determination of the rate of oxidation as it effects the rate of association. Tertiary alcohols lacking an alpha hydrogen are selected against and generally do not oxidize in the presence of Fétizon's reagent.

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