Swern oxidation
| Swern oxidation | |
|---|---|
| Named after | Daniel Swern |
| Reaction type | Organic redox reaction |
| Identifiers | |
| Organic Chemistry Portal | swern-oxidation |
| RSC ontology ID | RXNO:0000154 |
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The Swern oxidation, named after Daniel Swern, is a chemical reaction whereby a primary or secondary alcohol is oxidized to an aldehyde or ketone using oxalyl chloride, dimethyl sulfoxide (DMSO) and an organic base, such as triethylamine. The reaction is known for its mild character and wide tolerance of functional groups.
The by-products are dimethyl sulfide (Me2S), carbon monoxide (CO), carbon dioxide (CO2) and — when triethylamine is used as base — triethylammonium chloride (Et3NHCl). Two of the by-products, dimethyl sulfide and carbon monoxide, are very toxic volatile compounds, so the reaction and the work-up needs to be performed in a fume hood. Dimethyl sulfide is a volatile liquid (B.P. 37 °C) with an extremely unpleasant odour.
The first step of the Swern oxidation is the low-temperature reaction of dimethyl sulfoxide (DMSO), 1a, formally as resonance contributor 1b, with oxalyl chloride, 2. The first intermediate, 3, quickly decomposes giving off CO2 and CO and producing chloro(dimethyl)sulfonium chloride, 4.
After addition of the alcohol 5, the chloro(dimethyl)sulfonium chloride 4 reacts with the alcohol to give the key alkoxysulfonium ion intermediate, 6. The addition of at least 2 equivalents of base — typically triethylamine — will deprotonate the alkoxysulfonium ion to give the sulfur ylide 7. In a five-membered ring transition state, the sulfur ylide 7 decomposes to give dimethyl sulfide and the desired ketone (or aldehyde) 8.
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