Alcohol Reactions: Swern Oxidation using DMSO

The Swern Oxidation is a reaction that involves a primary/secondary alcohol starting reactant, oxayly chloride ((COCl)2), dimethyl sulfoxide (DMSO), and triethylamine (Et3N). When a primary alcohol is used, the corresponding aldehyde is formed. Similarly, when a secondary alcohol is used, the corresponding ketone is formed:

Primary Alcohol

Secondary Alcohol

This reaction only occurs with primary and secondary alcohols (tertiary alcohols will not react).

The reaction mechanism is depicted below:

Mechanism

In the first step, DMSO transforms into its reosnance structure with a negatively charged oxygen and positively charged sulfur.

In the second step, the transformed DMSO reacts with (COCl)2, removing one of the Cl groups to allow the binding of the DMSO moiety.

In the third step, the newly released chloride ion attacks the sulfur atom, causing an electron rearrangement forming a chlorosulfonium salt. Carbon dioxide (CO2) and carbon monoxide (CO) are released from the reaction at this stage as well.

In the fourth step, the alcohol-oxygen atom attacks the chlorosulfonium salt, adding it to the molecule.

In the fifth step, the free chloride ion attacks the hydrogen atom attached to the alcohol-oxygen, sending the electrons from the hydrogen bond to the oxygen atom.

In the sixth step, the free electrons on the triethylamine deprotonates one of the methyl groups that are present from the chlorosulfonium salt moiety.

In the seventh and final step, the negatively charged carbon atom attacks the hydrogen atom attached to the alcohol-carbon, causing the electrons from the hydrogen bond to go to the oxygen atom and the bond between the oxygen and sulfur breaks, giving the electrons to the positively charged sulfur. The result is the ketone product (in this example).

Practice this reaction using our Reaction Solver!