Chapter 14 Ethers, Epoxides,

and Sulfides

Jo BlackburnRichland College, Dallas, TX

Dallas County Community College District2006,Prentice Hall

Organic Chemistry, 6th EditionL. G. Wade, Jr.

Chapter 14 2

Introduction• Formula R-O-R where R and R are

alkyl or aryl.• Symmetrical or unsymmetrical• Examples:

O CH3

CH3 O CH3 O

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Chapter 14 3

Structure and Polarity• Bent molecular geometry• Oxygen is sp3 hybridized• Tetrahedral angle

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Chapter 14 4

Boiling PointsSimilar to alkanes of comparable molecular weight.

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Chapter 14 5

Hydrogen Bond Acceptor• Ethers cannot H-bond

to each other.• In the presence of

-OH or -NH (donor), the lone pair of electrons from ether forms a hydrogen bond with the -OH or -NH.

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Chapter 14 6

Solvent Properties

• Nonpolar solutes dissolve better in ether than in alcohol.

• Ether has large dipole moment, so polar solutes also dissolve.

• Ethers solvate cations. • Ethers do not react with

strong bases. =>

Chapter 14 7

Ether Complexes

• Grignard reagents

• Electrophiles

• Crown ethers

O B

H

H

H

+ _

BH3 THF

=>

Chapter 14 8

Common Names of Ethers

• Alkyl alkyl ether• Current rule: alphabetical order• Old rule: order of increasing complexity• Symmetrical: use dialkyl, or just alkyl.• Examples:

CH3CH2 O CH2CH3

diethyl ether orethyl ether

CH3 O C

CH3

CH3

CH3

t-butyl methyl ether ormethyl t-butyl ether =>

Chapter 14 9

IUPAC Names

• Alkoxy alkane• Examples:

CH3 O C

CH3

CH3

CH3

2-methyl-2-methoxypropane

O CH3

Methoxycyclohexane

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Chapter 14 10

Cyclic Ethers• Heterocyclic: oxygen is in ring.

• Epoxides (oxiranes) H2C CH2

O

• OxetanesO

• Furans (Oxolanes )O O

• Pyrans (Oxanes )O O

•DioxanesO

O

=>

Chapter 14 11

Naming Epoxides

• Epoxy attachment to parent compound, 1,2-epoxy-cyclohexane

• Alkene oxide, from usual synthesis methodperoxybenzoic acid

O

H

H

cyclohexene oxide

• Oxirane as parent, oxygen number 1

trans-2-ethyl-3-methyloxiraneOH

H

CH3CH3CH2

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Chapter 14 12

Spectroscopy of Ethers• IR: Compound contains oxygen, but

O-H and C=O stretches are absent.• MS: -cleavage to form oxonium ion, or

loss of either alkyl group.• NMR: 13C-O signal between 65-90,

1H-C-O signal between 3.5-4.

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Chapter 14 13

Williamson Synthesis

• Alkoxide ion + 1 alkyl bromide (or tosylate)• Example:

CH3 O H

CH3

CH3

+ K CH3 O

CH3

CH3

_K+

CH3 O

CH3

CH3

_+ CH3CH2 C

H

H

Br CH3 O

CH3

CH3

CH2CH2CH3 + Br_

=>

Chapter 14 14

Phenyl Ethers

• Phenoxide ions are easily produced for use in the Williamson synthesis.

• Phenyl halides or tosylates cannot be used in this synthesis method.

O H

+ NaOH

O_

Na+

+ HOH

=>

Chapter 14 15

Alkoxymercuration-Demercuration

Use mercuric acetate with an alcohol to add RO-H to a double bond and form the Markovnikov product.

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Chapter 14 16

Bimolecular Dehydration of Alcohols

• Industrial method, not good lab synthesis.• If temperature is too high, alkene forms.

=>

H O CH2CH3CH3CH2 O H CH3CH2 O CH2CH3+H2SO4

140°C

Chapter 14 17

Cleavage of Ethers

• Ethers are unreactive toward base, but protonated ethers can undergo substitution reactions with strong acids.

• Alcohol leaving group is replaced by a halide.

• Reactivity: HI > HBr >> HCl

=>

Chapter 14 18

Mechanism for Cleavage

CH3 O CH3 H Br CH3 O CH3

H_

Br_

++

Br_ +CH3 O CH3

H

Br CH3 + H O CH3

• Ether is protonated.

• Alcohol leaves as halide attacks.

• Alcohol is protonated, halide attacks, and another molecule of alkyl bromide is formed. =>

Chapter 14 19

Phenyl Ether Cleavage

• Phenol cannot react further to become halide.

• Example:

O CH2CH3HBr

OH

+ CH3CH2 Br

=>

Chapter 14 20

Autoxidation of Ethers

• In the presence of atmospheric oxygen, ethers slowly oxidize to hydroperoxides and dialkyl peroxides.

• Both are highly explosive.• Precautions:

Do not distill to dryness.Store in full bottles with tight caps.

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Chapter 14 21

Sulfides (Thioethers)

• R-S-R, analog of ether.• Name sulfides like ethers, replacing

“sulfide” for “ether” in common name, or “alkylthio” for “alkoxy” in IUPAC system.

• Example:S CH3 methyl phenyl sulfide

ormethylthiobenzene =>

Chapter 14 22

Thiols and Thiolates• R-SH about same acidity as phenols.

CH3CH2 SH + NaOH Na+ + HOHCH3CH2 S_

• Thiolates are better nucleophiles, weaker bases, than alkoxides.

CH3 C CH3

H

Br

CH3OH

CH3S_

CH3 C CH3

H

SCH3

2 halide Substitution product =>

Chapter 14 23

Sulfide Reactions

• Sulfides are easily oxidized to sulfoxides and sulfones.

CH3 S CH3H2O2

CH3COOHCH3 S CH3

O

CH3COOHH2O2 CH3 S CH3

O

O

• Sulfides react with unhindered alkyl halides to give sulfonium salts.

+CH3 S CH3 CH3 I CH3 S CH3

CH3

+I_

=>

Chapter 14 24

Synthesis of Epoxides• Peroxyacid epoxidation

• Cyclization of Halohydrin

HH

H2O, Cl2ClH

HO H OH_

ClH

O H_

H H

O

=>

Chapter 14 25

Ring Opening in Acid• Trans diol formed in water solvent.

• Alkoxy alcohol formed in alcohol solvent.

• 1,2-Dihalide formed with HI or HBr. =>

H

O

H

H+, H2O

H

HO H

OH

H

O

H

H+, CH3OH

H

HO H

OCH3

Chapter 14 26

Biosynthesis of Steroids

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Chapter 14 27

Ring Opening in BaseEpoxide’s high ring strain makes it

susceptible to nucleophilic attack.

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Chapter 14 28

Epoxide Opening in Base• With aqueous hydroxide, a trans 1,2-diol

is formed.• With alkoxide in alcohol, a trans 1,2-

alkoxy alcohol is formed.• These are the same products that were

formed in acid. • Different products are formed in acid and

base if epoxide is unsymmetrical. =>

Chapter 14 29

Orientation of Epoxide Opening

• Base attacks the least hindered carbon.

• In acid, the nucleophile attacks the protonatedepoxide at the most substituted carbon.

CH3CH2OHHC CH2

CH3

OH

OCH2CH3

_

HC CH2

CH3

O

OCH2CH3OCH2CH3

HC CH2

CH3

O

=>

HC CH2

OHH3C

OCH2CH3+

HC CH2

OHH3C

OCH2CH3HCH3CH2OH

+

HC CH2

CH3

O

H

Chapter 14 30

Reaction with Grignard and R-Li

• Strong base opens the epoxide ring by attacking the less hindered carbon.

• Example:

H2C CHCH3

O+

MgBr1) ether

2) H3O+

CH2 CHCH3

OH

=>

Chapter 14 31

Epoxy Resins

Polymer of bisphenol A and epichlorohydrin

HO C

CH3

CH3

OH

bisphenol A

H2C CHCH2ClO

epichlorohydrin

=>

Chapter 14 32

End of Chapter 14