Jones Reagent Density

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The Jones oxidation is one of the most widely used organic oxidations for the conversion of secondary alcohols to ketones and of primary allylic and benzylic alcohols to carboxylic acids. The reaction is often used in breathalyzers to detect the presence of alcohol. It is a simple, fast and economical method for converting alcohols to aldehydes that may then be further oxidized to carboxylic acids. This reaction can be conducted in a variety of solvents, including acetone. Infrared spectroscopy can be useful for monitoring the oxidation process.

The reaction uses a mixture of sodium or potassium dichromate in sulfuric acid to effect an oxidation of alcohols that produces aldehydes and may also be converted to carboxylic acids. The oxidation is rapid and exothermic. It can be modified to allow oxidation of some alcohols without producing aldehydes, such as by adding a strong base. In the case of benzylic alcohols the reaction is mild enough to avoid oxidation of the sensitive triple bond.

This reaction is not usually performed in aqueous solution because the chromate compounds are toxic. They must be added to an acetone solution and the reaction is carried out in a darkened vessel such as a beaker. The orange colored Cr(VI) is reduced to the blue green chromium (III) species by the action of the acetone.

There are many other chromate oxidants that are much safer than chromic acid. These include pyridinium chlorochromate, C5H5NH(+)CrO3Cl (abbreviated PCC), which is used in methylene chloride solutions and pyridinium dichromate, C5H5NH(+)2Cr2O7(-2) (abbreviated PDC), which is typically employed in a DMF solution. Both reagents are effective at oxidizing 1o-alcohols to aldehydes, although PCC oxidizes saturated 1o-alcohols more quickly than Jones reagent.