Jones oxidation
| Jones oxidation | |
|---|---|
| Named after | Ewart Jones |
| Reaction type | Organic redox reaction |
| Identifiers | |
| Organic Chemistry Portal | jones-oxidation |
| RSC ontology ID | RXNO:0000356 |
The Jones oxidation is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones.
Jones reagent is a solution of chromium trioxide in dilute sulfuric acid and acetone. A mixture of potassium dichromate and dilute sulfuric acid can also be used. The solvent acetone markedly affects the properties of the chromic acid. The oxidation is very rapid, quite exothermic, and the yields are typically high. The reagent rarely oxidizes unsaturated bonds.
Jones reagent will convert primary and secondary alcohols to aldehydes and ketones, respectively. Depending on the reaction conditions, the aldehydes may then be converted to carboxylic acids. For oxidations to the aldehydes and ketones, two equivalents of chromic acid oxidize three equivalents of the alcohol:
For oxidation of primary alcohols to carboxylic acids, one equivalent of Jones reagent is required for each substrate. The aldehyde is an intermediate.
The inorganic products are green, characteristic of chromium(III) aquo complexes.
Like many other oxidations of alcohols by metal oxides, the reaction proceeds via the formation of a mixed ester: These esters have the formula CrO3(OCH2R)−
Like conventional esters, the formation of this chromate ester is accelerated by the acid. These esters can be isolated when the alcohol lacks α-C-H bonds. For example, using tert-butyl alcohol, one can isolate ((CH3)3CO)2CrO2 (which is a good oxidant). The chromate esters degrade, releasing the carbonyl product and an ill-defined Cr(IV) product:
The partially deuterated alcohols HOCD2R oxidize about six times slower than the undeuterated derivatives. This large kinetic isotope effect shows that the C–H (or C-D) bond breaks in the rate-determining step. The reaction stoichiometry implicates the Cr(IV) species "CrO2OH−", which comproportionates with the chromic acid to give a Cr(V) oxide, which also functions as an oxidant for the alcohol.
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