Jones oxidation chromium reagents

Interestingly, in Jones oxidation, chromic acid is almost always generated from chromium trioxide while in the rest of the chromic acid oxidations, sodium or potassium dichromate are almost exclusively used. This seems to be the result of an irrational tradition originated since the reagents... 

Finally, Cr(VI)-reagents should be mentioned for example the Jones reagent (H2S04/Cr03 in acetone) for the oxidation of primary alcohols to carboxylic acids and the oxidation of secondary alcohols to the corresponding ketones. The main problem with these chromium reagents is their high toxicity. 

JONES OXIDATION / OXIDATION OF ALCOHOLS BY CHROMIUM REAGENTS... 

Jones Oxidation/Oxidation of Alcohols by Chromium Reagents.228... 

Ando s synthesis of hymenolin. xhis chromium trioxide/acetone/sulfuric acid reagent is often referred to as the Jones reagent, and oxidation of alcohols with this reagent is called Jones oxidation. Direct conversion of a primary alcohol to an acid is seen in the oxidation of 20 to 21, quantitatively, in Omura, Smith and coworker s synthesis of (+)-lactacystin.5 Jones oxidation is especially useful for molecules that contain alkenyl or alkynyl groups. 2 Oxidation of alcohols is usually faster in acetone than in acetic acid, and using a large excess of acetone protects the ketone product from further oxidation. - Many primary alcohols are oxidized... 

Note Jones reagent is a solution of chromium trioxide or potassium dichromate in dilute sulfuric acid and acetone. Acetone markedly affects the properties of chromic acid. Oxidation is very rapid, usually exothermic, and the yields are typically high. This reagent rarely oxidizes unsaturated bonds. 

When a solution of chromic and sulfuric acids in water is added at 0-20° to an alcohol or formate dissolved in acetone, a rapid oxidation takes place with the separation of the green chromium III reduction product as a separate layer. This system is commonly known as Jones reagent. The rate of oxidation is so fast that it is often possible to run the reaction as a titration to an... 

A variety of chromium (VI) oxidizing systems have been developed which allow for the oxidation of a wide range of sensitive compounds. One of the most widely used chromium (VI) reagents is the Jones reagent (/), whose use is detailed in the procedure. A related system employs acetic acid as the solvent, and an example of this reagent is also given. 

Various experimental conditions have been used for oxidations of alcohols by Cr(VI) on a laboratory scale, and several examples are shown in Scheme 12.1. Entry 1 is an example of oxidation of a primary alcohol to an aldehyde. The propanal is distilled from the reaction mixture as oxidation proceeds, which minimizes overoxidation. For secondary alcohols, oxidation can be done by addition of an acidic aqueous solution containing chromic acid (known as Jones reagent) to an acetone solution of the alcohol. Oxidation normally occurs rapidly, and overoxidation is minimal. In acetone solution, the reduced chromium salts precipitate and the reaction solution can be decanted. Entries 2 to 4 in Scheme 12.1 are examples of this method. 

Jones reagent is prepared by dissolving chromium oxide (C1O3) (23.5 g) in coned sulfuric acid (21 mL) with cooling and then diluting with distilled water to give a total volume of 175 mL.4... 

All of the usual chromium-based oxidation reagents that have been used for the oxidation of cyclobutanols to cyclobutanones, for example, chromium(VI) oxide (Jones reagent),302 pyri-dinium chlorochromate,304 pyridinium dichromate,307 and chromium(YI) oxide/pyridine (Collins),303 are reported to do so without any serious problems. Alternatively, tetrapropylam-monium perruthenate in the presence of A-methylmorpholine A -oxide. oxalyl chloride in the presence of triethylamine in dimethyl sulfoxide (Swern),158,309,310 or phenyl dichlorophos-phate in the presence of triethylamine and dimethyl sulfoxide in dichloromethane (Pfitzner-Moffatt),308 can be used. The Pfitzner-Moffatt oxidation procedure is found to be more convenient than the Swern oxidation procedure, especially with respect to the strict temperature control that is necessary to achieve good yields in the latter, e.g. oxidation of 1 to give 2.308... 

Many other reagents and procedures have been developed for oxidizing alcohols. Some are simply modifications of the procedures we have seen. For example, the Collins reagent is a complex of chromium trioxide and pyridine, the original version of PCC. The Jones reagent is a milder form of chromic acid a solution of diluted chromic acid in acetone. 

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