Swern Oxidation

The oxidation of 1° and 2° alcohols to the corresponding aldehyde or ketone, using DMSO and oxalyl chloride is known as the Swern oxidation. First DMSO is activated by oxalyl chloride, releasing CO and CO₂ gas to make a chlorosulfonium salt. The alcohol then attacks the chlorosulfonium salt and deprotonation by triethylamine (TEA) forms an alkoxysulfonium ylide. A proton transfer and rearrangement produces the final carbonyl compound and dimethyl sulfide.

• Care should be taken while running the reaction as DMSO reacts violently with oxalyl chloride in the absence of a solvent.
• The chlorosulfonium salt is unstable above -60°C, so the oxidation is usually conducted at -78°C.
• Steric hindrance of the substrate does not influence the efficiency of the oxidation.
• Side reactions with oxalyl chloride are rare. If trifluoroacetic anhydride (TFAA) is used instead, side products are to be expected.

• Reagents: DMSO, Oxalyl Chloride, Solvent (DCM), Tertiary Amine (TEA, DIPA)
• Reactant: 1° or 2° Alcohol
• Product: Aldehyde or Ketone
• Type of Reaction: Activated DMSO Oxidation
• Bond Formation: C=O

Mechanism

Original Paper

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