Swern oxidation

The Swern oxidation uses dimethylsulfoxide and oxalyl chloride, followed by addition of a base such as triethylamine. The actual oxidizing species in this reaction is the dimethylchlorosulfonium ion, which forms from dimethylsulfoxide and oxalyl chloride.

The mechanism is included below, for reference:

Oxidation-Swern Oxidation (Stage1)

In the first stage dimethylsulfoxide (DMSO) reacts with oxalyl chloride to give an electrophilic sulfur compound, which collapses to give a chlorosulfonium ion, CO₂ and CO.

Oxidation-Swern Oxidation (Stage2)

In the second stage the alchohol reacts with the chlorosulfonium ion to give a new sulfonium salt and HCl.

Oxidation-Swern Oxidation (Stage3)

In the final stage the base (Et₃N) is added to deprotonate the salt, which then collapses to give the desired aldehyde or ketone and dimethyl sulfide.