Chp 18: Esters, Epoxides, Thiols and Sulfides

preparation of ethers:

1. Williamson ether synthesis requires..

1. an alcohol

2. primary alkyl halide or primary tosylate

3. a strong base (ex: NaOH, NaNH2)

1. classification

2. IUPAC

3. Common name

1. unsymmetrical

2. ethyl methyl ether

3. 1- methoxy ethane

1. classification

2. IUPAC

3. Common name

1. symmetrical

2. diethyl ether

3. 1- ethoxy ethan

1. classification

2. Common name

1. cyclic

2. Tetrahydrofuran (THF)

Reaction of ethers: Using HBr or HI

• HCl does not cleave ethers because 

Bromine and Iodine are larger than Chlorine and therefore can stabilize the negative charge much better than leaving groups

ether mechanisms:

• ethers with primary or secondary alkyl groups (SN2)

nucleophile attacks the least sterically hindered carbon

ether mechanisms: (benzylic or allylic)

• ethers with tertiary alkyl groups (SN2 or E1)

• a protonated epoxide can form a stable tertiary carbocation intermediate that is then attacked by a weak nucleophile (halide)

• 4 product reaction

reactions of epoxides: ring opening

• base catalyzed epoxide ring opening is ALWAYS…

SN2 mechanism: Nucleophile attacks the less hindered carbon

if the epoxide has a primary or secondary carbon…

the mechanism will be SN2

if epoxide has a tertiary, benzylic or allylic carbon…

the mechanism will be SN1

Williamson ether synthesis

Alkoxymercuration-demurcuration ether synthesis

Ethers with secondary alkyl groups

SN2 mechanism (2 products)

Reactions of epoxides: ring opening

Base-catalyzed epoxied ring opening is ALWAYS SN2

Thiol to sulfide synthesis

Epoxied with primary or secondary carbon

SN2 mechanism

SN1 mechanism

Naming ethers

Alphabetize the alkyl groups -ether