Synthesis of Ethers via Acid-catalyzed Condensation of Alcohols

Summary

• Reagents typically H₂SO₄ and heat.
• In general, typically limited to symmetrical ethers of primary alcohols.
• The method is not suitable for unsymmetrical ethers.
• The substitution involves the O nucleophile of one alcohol attacking the electrophilic C in the other displacing a water molecule.

Questions:
Why can this reaction be termed a condensation reaction ? 
Why is the reaction unsuitable for unsymmetrical ether synthesis ? 

Related reactions

• Williamson ether synthesis

MECHANISM FOR  OF ALCOHOL CONDENSATION TO GIVE AN ETHER
Step 1: An acid/base reaction. Protonation of the alcoholic oxygen to make a better leaving group. This step is very fast and reversible.  The lone pairs on the oxygen make it a Lewis base.
Step 2: The O of the second alcohol molecule functions as the nucleophile and attacks to displace the good leaving group, a neutral water molecule, by cleaving the C-O bond. This creates an oxonium ion intermediate.
Step 3: Another acid / base reaction. The proton is removed by a suitable base (here a water molecule, ROH is another alternative) to give the ether product.

Williamson Ether Synthesis

Summary

• Reagents: typically use Na metal as the base to generate the alkoxide then add the alkyl halide.
• Since the reaction is S_N2, the halide should be methyl or primary.
• Alkoxide character (primary, secondary or tertiary) is less important.
• This reaction is suitable for either symmetrical or unsymmetrical ethers.
• The method could also be used for cyclic ethers.

Questions:
What reaction is likely to interfere if the halide is tertiary ?
Can you write a balanced equation for the reaction of sodium metal with the alcohol ? 
What is the oxidation state and charge of the sodium metal ? 
What makes the methyl and primary halides most suitable ? 

Related Reactions

• Ether synthesis via Alcohol condensation
• Substitution Reactions of Alkyl Halides

MECHANISM OF THE WILLIAMSON ETHER SYNTHESIS
The alkoxide functions as the nucleophile and attacks the electrophilic C of the alkyl halide displacing the bromide and creating the new C-O bond.

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