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Chapter 15: Alcohols, Diols and Thiols



Overview | Reaction of Alcohols with Hydrogen Halides | Reaction with SOCL2, PX3 to give Alkyl Halides | Acid catalyzed Dehydration | Synthesis of Ethers | Synthesis of Esters | Oxidation | Cleavage of 1,2-Diols |


Synthesis of Ethers

Chapter 15: Alcohols, Diols and Thiols

Synthesis of Ethers

There are several methods for the synthesis of ethers starting from alcohols:
 
 

Acid catalyzed condensation of Alcohols
condensation of alcohols

Williamson Ether synthesis (Ch16)
Williamson ether synthesis
Alkoxymercuration-demercuration (review)
alkoxymercuration-demercuration
Ring opening of Epoxides
alkoxide opening of epoxides

Synthesis of Ethers via Acid-catalyzed Condensation of Alcohols

ether synthesis by alcohol condensation
Reaction type: Nucleophilic Substitution (SN2)

Summary

Questions:
Why can this reaction be termed a condensation reaction ? a small molecule, here water, is displaced
Why is the reaction unsuitable for unsymmetrical ether synthesis ? lack of control of the protonation and which alcohol functions as the Nu

Related reactions

MECHANISM FOR 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.
acid-catalysed alcohol condensation mechanism
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

an alkoxide Nu attacks an alkyl halide to give the ether
Reaction type: Nucleophilic Substitution (SN2)

Summary

Questions:
What reaction is likely to interfere if the halide is tertiary ?Elimination to give an alkene (see Ch 5)
Can you write a balanced equation for the reaction of sodium metal with the alcohol ? 2 ROH + 2 Na  =  2 RONa + H2
What is the oxidation state and charge of the sodium metal ? Both are zero
What makes the methyl and primary halides most suitable ? S<sub>N</sub>2 reaction so minimise steric interactions

Related Reactions

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.
Williamson ether synthesis : a simple S<sub>N</sub>2 reaction

Alkoxymercuration-Demercuration of Alkenes
(review of Chapter 14)

alkene alkoxymercuration-demercuration to give an alcohol
Reaction type:  Electrophilic Addition

Summary

a mercurinium ion
Questions: Related reactions

 


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