Oxidation of Primary Alcohols To Carboxylic Acids - Jones Oxidation

Jones Oxidation

The so-called Jones reagent is prepared by dissolving chromium trioxide (CrO₃) in aqueous sulfuric acid, which results in formation of a reddish solution containing chromic acid (H₂CrO₄) and oligomers thereof. Addition of Jones reagent to a solution of a primary alcohol in acetone — as first described by Jones — results in oxidation of the alcohol to a carboxylic acid. This classical protocol, involving a direct addition, is used very often regardless of the fact that it frequently leads to the formation of substantial amounts of esters — possessing the structure R-CO-O-CH₂-R — derived from oxidative dimerization of primary alcohols. Holland and Gilman proved that this side reaction can be greatly suppressed by following the inverse addition protocol whereby a solution of the primary alcohol in acetone is slowly added to Jones reagent under conditions as dilute as practical.

Jones reagent interacts with secondary alcohols resulting in oxidation to ketones. Treatment of compounds, containing both primary and secondary alcohols, with Jones reagent leads to formation of ketoacids.

Problems encountered with the use of large quantities of chromium trioxide, which is toxic and dangerous for the environment, prompted the development by Zhao of a catalytic procedure, involving treatment with excess of periodic acid (H₅IO₆) in presence of about 1.2 mol% of CrO₃. Zhao's procedure for the use of catalytic CrO₃ is very well-suited for reactions on a large scale.