11.3: Ethers from Alcohols: Alcohol Dehydration and Williamson Ether Synthesis
Overview
Ethers can be prepared from organic compounds by various methods. Some of them are discussed below,
Preparation of Ethers by Alcohol Dehydration
In this method, in the presence of protic acids, alcohol dehydrates to produce alkenes and ethers under different conditions. For example, in the presence of sulphuric acid, dehydration of ethanol at 413 K yields ethoxyethane, whereas it yields ethene at 443 K.
This method is a nucleophilic substitution reaction. The two alcohol molecules involved in the reaction play two roles—one alcohol molecule acts as a substrate while the other acts as a nucleophile. The reaction follows an SN2 mechanism. The dehydration of secondary and tertiary alcohols to get corresponding ethers is unsuccessful as alkenes are formed easily in these reactions.
Preparation of Ethers by Williamson Ether Synthesis
It is the most versatile method for the preparation of asymmetrical ethers in laboratories. In this method, initially, the alcohol is deprotonated to form an alkoxide ion. Further, the alkoxide ion functions as a nucleophile and attacks an alkyl halide, leading to the formation of ether. The reaction generally follows the SN2 mechanism for primary alcohol.
Williamson synthesis exhibits higher productivity when the halide to be displaced is on a methyl or a primary carbon. In the case of secondary alkyl halides, elimination competes with substitution, whereas the formation of elimination products is the only case in tertiary alkyl halides.
