Williamson ether synthesis
The Williamson synthesis (see also Ether Synthesis ) is used to produce symmetrical and unsymmetrical ethers. It was developed in the 19th century by its namesake Alexander William Williamson. The Williamson synthesis is a special case of the nucleophilic substitution (SN ), in which the nucleophile is an alkoxide (alkyl -O-, aryl-O-, etc.) is used. The reaction mechanism corresponds to an SN1 or SN2 reaction:
The Williamson ether synthesis is a two-step process in their technical implementation. First, it must be made of the alcohol component, an alkoxide, usually by reaction of the alcohol with elemental sodium or potassium. Alternatively, you can work well with the corresponding hydrides, sodium hydride or potassium hydride. The latter option has the advantage that the hydrides in moist air are more stable and are better than powdered materials ponderable.
In a second stage, the alcoholate is reacted with the electrophile. As electrophiles, the alkyl chlorides, bromides or iodides are used frequently, and sulfonic acid esters such as the p- toluenesulfonic acid or methanesulfonic acid are used.
A suitable solvent for the reaction, either the alcohol itself or another polar solvent such as dimethylsulfoxide (DMSO ), dimethylformamide (DMF) or hexamethylphosphoramide ( HMPA ).
As ethers often are volatile compounds, it can usually be distilled off continuously during the reaction from the reaction mixture.
The Williamson ether synthesis is possible not usually with tertiary haloalkanes. When trying to implement it with alkoxides to ethers takes place instead of the Williamson synthesis ( = substitution) elimination to form an alkene. The result for example from the reaction of 2- iodo-2- methylpropane with sodium 2-methyl -prop -1-ene ( isobutene ), and not the ether:
An ether can only be produced in this manner, if one uses the tertiary alkyl radical as alkoxide component.
A special case of the Williamson ether synthesis is the use of silver (I ) oxide to the etherification of alcohols and alkyl halides.