The most common general method for the synthesis of ether is Williamson ether synthesis, involves nucleophilic displacement of a halide ion or other good leaving group by an alkoxide ion. The name of the reaction was coined after Alexander William Williamson developed it in 1850. Williamson Ether Synthesis is a reaction that uses deprotonated alcohol and an organohalide to form an ether.
Williamson Ether Synthesis usually takes place as an SN2 reaction of a primary alkyl halide with an alkoxide ion. The structure of ethers was proved due to this chemical reaction. SN2 pathway is required for the synthesis this reaction is useful only when the alkyl halide is primary or secondary. The Ethers produced in this way have more carbon atoms than either of the starting materials and thus are more complex structures.
Thus Organic chemistry’s history holds a special place for the reaction. Read Williamson Ether Synthesis and its uses.
The basic mechanism of the reaction is:
Diethyl Ether and Sodium Chloride are formed when Sodium Ethoxide and Chloroethane a react. The reaction is displayed below.
Na+C2H5O− + C2H5Cl → C2H5OC2H5 + Na+Cl−
For example, consider the following Williamson Ether Synthesis reaction.
Mechanism of the Reaction
- The nucleophile attacks the alkyl halide forming an ether from the back.
- This response takes place in a single step, which is both cleavage and bond formation.
- If halides are sterically impeded then alkoxide acts as a basis and protons in β-place are accessible.
- The products derived from a response to elimination.
Uses of Ether
- The preparation of ethers in labs and industrially is mostly done through this process. Symmetrical and asymmetrical both forms of ethers are simply prepared.
- Two choices of reactants are available which is finally agreed upon depending on the reactivity and availability.
- Two alcohols are also used to produce ethers by Williamson reaction. The two are reacted together after one of them is transformed a leaving group (tosylate).
- The alkylating agent is preferred to be primary whereas the alkoxide could be primary secondary or tertiary. If not a Halide, a sulfonate ester created for the purpose of the reaction are the leaving group.
- In situ preparation of alkoxide ions is done as they are extremely reactive.
- Potassium hydroxide or a carbonate base is used for the laboratory preparation, whereas phase transfer catalysis is used when doing industrial synthesis.
- Acetonitrile and N, N-dimethylformamide are used as solvents.
- It takes around 1-8 hours to complete the reaction and it takes place at a temperature of around 50-100°C.
- One can get a yield of between 50-95% in the lab preparation as using up the raw material completely is rare, due to side reactions.
- The industrial procedure shows better quantitative results.
- Lab synthesis does not usually require a catalyst but if the alkylating agent is unreactive then to improve the rate of reaction iodide salt can be added which yields an extremely reactive iodide after a halide exchange with the chloride.
- Silver salts like Silver Oxide are used in extreme cases which helps the leaving halide group and makes its exodus more simple.
Limitations of the Reaction
There are few limitations of Williamson Ether Synthesis.
- Tertiary alkyl halides or sterically hindered primary or secondary alkyl halides tend to undergo E2 elimination in the presence of the alkoxide that in addition to being a nucleophile also act as a base.
- Alkali phenoxides may undergo C-alkylation in addition to expected O-alkylation.
- This process for preparing ethers is too limited to be of any practical value for synthetic organic chemists.
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