Chapter 14 Ethers, Epoxides, and Sulfides
Chem 233 Dr. Hoeger
Introduction • Formula R-O-R′ where R and R′ are alkyl or aryl. • Symmetrical or unsymmetrical • Examples:
CH3 O CH3 O
O CH3
Ethers Ethers 2
1 Structure and Polarity
• Bent molecular geometry • Oxygen is sp3 hybridized • Tetrahedral angle
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Ethers Ethers 3
Boiling Points
Similar to alkanes of comparable molecular weight.
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Ethers Ethers 4
2 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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Ethers Ethers 5
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. =>
Ethers Ethers 6
3 Ether Complexes
• Grignard reagents
H + _ • Electrophiles O B H H
BH3 THF
• Crown ethers
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Ethers Ethers 7
Common Names of Ethers
• Alkyl alkyl ether • Current rule: alphabetical order • Old rule: order of increasing complexity • Symmetrical: use dialkyl, or just alkyl. • Examples:
CH3
CH3 O C CH3 CH3CH2 O CH2CH3 CH3 diethyl ether or t-butyl methyl ether or ethyl ether methyl t-butyl ether => Ethers Ethers 8
4 IUPAC Names • Alkoxy alkane • Examples:
CH 3 O CH3 CH3 O C CH3
CH3 2-methyl-2-methoxypropane Methoxycyclohexane
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Ethers Ethers 9
Cyclic Ethers
• Heterocyclic: oxygen is in ring.
O Epoxides (oxiranes) • H2C CH2 O • Oxetanes
• Furans (Oxolanes ) O O
• Pyrans (Oxanes ) O O O •Dioxanes => O Ethers Ethers 10
5 Naming Epoxides
• Alkene oxide, from usual synthesis method H peroxybenzoic acid O cyclohexene oxide H • Epoxy attachment to parent compound, 1,2-epoxy-cyclohexane • Oxirane as parent, oxygen number 1 O H CH3 trans-2-ethyl-3-methyloxirane => CH3CH2 H
Ethers Ethers 11
Spectroscopy of Ethers
• IR: Compound contains oxygen, but O-H and C=O stretches are absent. • MS: α-cleavage to form oxonium ion, or loss of either alkyl group. • NMR: 13C-O signal between δ65-δ90, 1H-C-O signal between δ3.5-δ4.
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Ethers Ethers 12
6 Williamson Synthesis
• Alkoxide ion + 1° alkyl bromide (or tosylate) • Example: CH 3 CH3 CH O H _ + 3 + K CH3 O K CH 3 CH3
CH3 H CH _ 3 _ CH O 3 + CH3CH2 C Br CH3 O CH2CH2CH3 + Br CH 3 H CH3 =>
Ethers Ethers 13
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 O Na+ + NaOH + HOH =>
Ethers Ethers 14
7 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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Ethers Ethers 15
Bimolecular Dehydration of Alcohols
• Industrial method, not good lab synthesis. • If temperature is too high, alkene forms.
H2SO4 CH3CH2 O H + H O CH2CH3 CH3CH2 O CH2CH3 140°C
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Ethers Ethers 16
8 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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Ethers Ethers 17
Mechanism for Cleavage • Ether is protonated. H
+ _ _ CH3 O CH3 H Br CH3 O CH3 + Br • Alcohol leaves as halide attacks. H _ + Br CH3 O CH3 Br CH3 + H O CH3
• Alcohol is protonated, halide attacks, and another molecule of alkyl bromide is formed. =>
Ethers Ethers 18
9 Phenyl Ether Cleavage • Phenol cannot react further to become halide. • Example:
O CH2CH3 OH HBr + CH3CH2 Br
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Ethers Ethers 19
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. =>
Ethers Ethers 20
10 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 or methylthiobenzene =>
Ethers Ethers 21
Thiols and Thiolates
• R-SH about same acidity as phenols.
_ + CH3CH2 SH + NaOH CH3CH2 S Na + HOH • Thiolates are better nucleophiles, weaker bases, than alkoxides. Br _ SCH3 CH3S CH3 C CH3 CH3 C CH3 CH3OH H H 2° halide Substitution product =>
Ethers Ethers 22
11 Sulfide Reactions
• Sulfides are easily oxidized to sulfoxides and sulfones.
O O H2O2 H2O2 CH3 S CH3 CH3 S CH3 CH3 S CH3 CH3COOH CH3COOH O
• Sulfides react with unhindered alkyl halides to give sulfonium salts.
+ _ CH3 S CH3 + CH3 I CH3 S CH3 I
CH3 =>
Ethers Ethers 23
Synthesis of Epoxides
• Peroxyacid epoxidation
• Cyclization of Halohydrin
_ _ HO H OH O H O H2O, Cl2 H H H H Cl H Cl H =>
Ethers Ethers 24
12 Ring Opening in Acid
• Trans diol formed in water solvent.
+ O H , H2O HO H
H H H OH • Alkoxy alcohol formed in alcohol solvent.
+ O H , CH3OH HO H
H H H OCH3
• 1,2-Dihalide formed with HI or HBr.
Ethers Ethers 25
Biosynthesis of Steroids
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Ethers Ethers 26
13 Ring Opening in Base
Epoxide’s high ring strain makes it susceptible to nucleophilic attack.
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Ethers Ethers 27
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. =>
Ethers Ethers 28
14 Orientation of Epoxide Opening
• Base attacks the least hindered carbon. _ O O OH CH3CH2OH HC CH2 HC CH2 HC CH2 CH CH OCH2CH3 CH OCH2CH3 3 OCH2CH3 3 3 • In acid, the nucleophile attacks the protonated epoxide at the most substituted carbon.
H OH H3C OH H3C + O HC CH2 HC CH2 HC CH 2 OCH2CH3 OCH2CH3 H + CH3 => CH3CH2OH Ethers Ethers 29
Reaction with Grignard and R-Li • Strong base opens the epoxide ring by attacking the less hindered carbon. • Example:
OH MgBr CH CHCH O 1) ether 2 3 H2C CHCH3 + + 2) H3O
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Ethers Ethers 30
15 Epoxy Resins
Polymer of bisphenol A and epichlorohydrin
CH3 O
HO C OH H2C CHCH2Cl epichlorohydrin CH3 bisphenol A
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Ethers Ethers 31
End of Chapter 14 Homework: 33, 35, 37, 39, 40, 42, 45-47
Ethers Ethers 32
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