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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
=>
Chapter 14 3
Structure and Polarity
• Bent molecular geometry
• Oxygen is sp3 hybridized
• Tetrahedral angle
=>
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.
=>
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
=>
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-methyloxiraneO
H
H
CH3
CH3CH2
=>
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.
=>
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.
=>
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.
=>
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
CH3COOH
H2O2CH3 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 27
Ring Opening in BaseEpoxide’s high ring strain makes it
susceptible to nucleophilic attack.
=>
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
OCH2CH3H
CH3CH2OH
+
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 CHCH2Cl
O
epichlorohydrin
=>