chapter 14 ethers, epoxides, and sulfides

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

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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

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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