Preparation of Ether
In williamson's synthesis, alkyl halides (primary and secondary) react with R'ONa (Sodium alkoxide) or R'OK (Potassium alkoxide) to produce ethers.
Tertiary alkyl halides are not used in Williamson's synthesis because tertiary alkyl halides prefer to undergo elimination (example of elimination is given in nucleophilic substitution reaction of haloalakanes ) instead of substitution. Hence, if we are to prepare t-Butyl methyl ether, we will use (CH3)3ONa and CH3Br; and not (CH3)3Br and CH3OH.
Complete the following reaction
Preparation of Ethers by Dehydration of Alcohols
When alcohols are heated with conc. H2SO4 at 413 K, ethers (ROR') are formed.
Preparation of Ether using Heated Alumina
The vapours of alcohols are passed over Al2O3 at 513-523 K to produce ether.
Preparation of Ether from Alkyl Halides
Alkyl halides are heated with dry silver oxide to form ether.
Question : Write the reactions of Williamson synthesis of 2-ethoxy-3-methylpentane starting from ethanol and 3-methylpentan-2-ol.
Answer : A primary alkyl halide is preferred in Williamson synthesis because it is less crowded. Thus, the alkyl halide should be derived from ethanol and the alkoxide ion from 3-methylpentan-2-ol.
Alkyl halide is derived from ethanol
Alkoxide ion is derived from 3-methylpentan-2-ol
The Williamson reaction is:
Preparation of 2-ethoxy-3-methylpentane
Question : Write the names of reagents and equations for the preparation of the following ethers by Williamson's synthesis:
- Sodium propoxide + 1-Bromopropane → 1-Propoxypropane
- Sodium phenoxide + Bromoethane → Ethoxybenzene
- Sodium 2-methyl-2-propoxide + Bromoethane → 2-Methoxy-2-methylpropane
- Sodium ethoxide + Bromomethane → 1-Methoxyethane