Swern-Oxidation

The Swern oxidation is a name reaction in organic chemistry, which was named after its discoverer, Daniel Swern. The reaction is a mild oxidation of primary or secondary alcohols to aldehydes or ketones with dimethyl sulfoxide, oxalyl chloride and triethylamine. One advantage of the Swern oxidation toward reactions with chromium reagents is the lower toxicity of the reagents. For the reaction is of vital importance that the reaction temperature remains well below room temperature, because the reagent formed in situ decomposes very rapidly at higher temperature. A temperature of -40 ° C is sufficiently low for the reaction. The further oxidation to carboxylic acids in the Swern oxidation is impossible. The disadvantage is mainly the very unpleasant smell of Dimethylsulfids formed in the reaction.

Overview reaction

In the Swern oxidation is oxidation of alcohols to ketones or aldehydes. The oxidizing agent activated dimethyl sulfoxide is used to activate oxalyl chloride and triethylamine as base.

Mechanism

In the first step, through a nucleophilic attack of the dimethyl sulfoxide (DMSO ) to the oxalyl chloride and after removal of carbon dioxide, carbon monoxide and chlorine, the active intermediate, the sulfonium ion is formed.

Both sulfonium ions, which occur in this reaction are the activated forms of dimethyl sulfoxide to form a sulfonium salt of the same alcohol. After the addition of an alcohol of this engages the sulfonium ion to nucleophilic. Thus, carbon dioxide, carbon monoxide and chlorine to be displaced with the first form of the sulfonium ion and chloride with the second mold is removed.

The base is triethylamine finally deprotonates the sulfonium ion and elimination of dimethyl sulfide, the aldehyde ( when R1 = H or R2 = H) or the ketone formed.