Jones oxidation is the most common oxidation method for converting primary alcohols to carboxylic acids. It is carried out either by CrO₃ in H₂SO₄, chromic acid itself, or a dichromate salt such as Na₂Cr₂O₇ in the presence of sulfuric acid.

The Mechanism of Jones Oxidation

The reaction starts with a nucleophilic addition of the alcohol to the protonated chromic oxide, forming a chromate ester. The Cr component of the ester is a good leaving group, which promotes an elimination reaction, forming the C=O bond of the intermediate aldehyde. Once the aldehyde is formed, it is converted into a hydrate via nucleophilic addition of water. The hydrate reacts just like the alcohol in the first part of the reaction, and the final product, carboxylic acid, is formed.

Jones Oxidation with Chromic Acid

As mentioned earlier, the reaction can also be carried out by using chromic acid itself, and follows the same pattern of converting the OH into a leaving group and an elimination forming the C=O double bond.

Because the oxidation of the alcohols goes all the way to carboxylic acid, Jones reagent is considered to be a strong oxidizing agent. We can use what is called a mild oxidizing agent, such as PCC, PDC, DMP, etc., to selectively convert primary alcohols to aldehydes.

Notice that secondary alcohols are oxidized to ketones regardless of whether a strong or a weak oxidizing agent is used. Tertiary alcohols cannot be oxidized.

Check out this comprehensive article for the selectivity and mechanism of the most common oxidizing agents you need for your organic chemistry class.

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