Oxidation of Alcohols to Aldehydes and Ketones

Alcohols can be oxidized to aldehydes and ketones using a variety of oxidizing agents. The outcome of the oxidation depends both on the oxidizing agent and the structure of the alcohol. Recall from the oxidation states of organic compounds that alcohols are below all the carbonyl compounds, and the aldehydes are between the alcohols and carboxylic acid derivatives:

So, to oxidize the alcohol to an aldehyde we need conditions that do not over oxidize it to a carboxylic acid. For this, we have what’s called mild oxidizing agents. The most common mild oxidizing agents are pyridinium chlorochromate (PCC), pyridinium dichromate (PDC), Swern oxidation using DMSO, (COCl)₂ and Et₃N, and the Dess-Martin (DMP) oxidation:

Strong oxidizing agents such as Jones reagent convert primary alcohols to carboxylic acids. On the other hand, secondary alcohols are always oxidized to ketones, whereas tertiary alcohols cannot be oxidized to any carbonyl as their structure simply does not allow this transformation.

These are the most common strong oxidizing agents you will need to know:

Here are some examples of mild oxidizing agents converting primary alcohols to aldehydes:

All the oxidation reactions of alcohols work based on the same principle of converting the OH into a good leaving group and eliminating the adjacent hydrogen to form a C=O double bond. It is essentially a type of an E2 reaction but instead of a C=C double bond, we are forming a C=O double bond.

This article is a summary of the patterns of oxidizing primary a secondary alcohols using different strong and mild oxidizing agents. We have a separate post with mechanistic details of all the oxidizing agents mentioned here, so feel free to check that out as well.

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