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Chapter 14 Ethers, Epoxides,
and Sulfides
Chem 233Dr. Hoeger
Ethers Ethers 2
Introduction• Formula R-O-R′ where R and R′ are alkyl
or aryl.• Symmetrical or unsymmetrical• Examples:
O CH3
CH3 O CH3 O
2
Ethers Ethers 3
Structure and Polarity
• Bent molecular geometry• Oxygen is sp3 hybridized• Tetrahedral angle
=>
Ethers Ethers 4
Boiling PointsSimilar to alkanes of comparable molecular weight.
=>
3
Ethers Ethers 5
Hydrogen Bond Acceptor• Ethers cannot H-bond to each other.• In the presence of
-OH or -NH (donor), the lone pair ofelectrons from ether forms ahydrogen bond with the -OH or-NH.
=>
Ethers Ethers 6
Solvent Properties
• Nonpolar solutes dissolvebetter in ether than inalcohol.
• Ether has large dipolemoment, so polar solutesalso dissolve.
• Ethers solvate cations.• Ethers do not react with
strong bases. =>
4
Ethers Ethers 7
Ether Complexes
• Grignard reagents
• Electrophiles
• Crown ethers
O B
H
H
H
+_
BH3 THF
=>
Ethers Ethers 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 =>
5
Ethers Ethers 9
IUPAC Names• Alkoxy alkane• Examples:
CH3 O C
CH3
CH3
CH3
2-methyl-2-methoxypropane
O CH3
Methoxycyclohexane
=>
Ethers Ethers 10
Cyclic Ethers
• Heterocyclic: oxygen is in ring.
• Epoxides (oxiranes) H2C CH2
O
• OxetanesO
• Furans (Oxolanes )O O
• Pyrans (Oxanes )O O
•DioxanesO
O
=>
6
Ethers Ethers 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
=>
Ethers Ethers 12
Spectroscopy of Ethers
• IR: Compound contains oxygen, butO-H and C=O stretches are absent.
• MS: α-cleavage to form oxonium ion, or loss of either alkylgroup.
• NMR: 13C-O signal between δ65-δ90, 1H-C-O signal between δ3.5-δ4.
=>
7
Ethers Ethers 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
_
=>
Ethers Ethers 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
=>
8
Ethers Ethers 15
Alkoxymercuration-DemercurationUse mercuric acetate with an alcohol to add RO-H to a double
bond and form the Markovnikov product.
=>
Ethers Ethers 16
Bimolecular Dehydrationof 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
9
Ethers Ethers 17
Cleavage of Ethers
• Ethers are unreactive toward base, but protonated ethers canundergo substitution reactions with strong acids.
• Alcohol leaving group is replaced by a halide.• Reactivity: HI > HBr >> HCl
=>
Ethers Ethers 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, andanother molecule of alkyl bromide is formed.=>
10
Ethers Ethers 19
Phenyl Ether Cleavage• Phenol cannot react further to become halide.• Example:
O CH2CH3
HBr
OH
+ CH3CH2 Br
=>
Ethers Ethers 20
Autoxidation of Ethers
• In the presence of atmospheric oxygen, ethers slowlyoxidize to hydroperoxides and dialkyl peroxides.
• Both are highly explosive.• Precautions:
Do not distill to dryness.Store in full bottles with tight caps.
=>
11
Ethers Ethers 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 =>
Ethers Ethers 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 =>
12
Ethers Ethers 23
Sulfide Reactions
• Sulfides are easily oxidized to sulfoxides and sulfones.
• Sulfides react with unhindered alkyl halides to give sulfoniumsalts.
+CH3 S CH3 CH3 I CH3 S CH3
CH3
+I
_
=>
CH3 S CH3
H2O2
CH3COOHCH3 S CH3
O
CH3COOH
H2O2CH3 S CH3
O
O
Ethers Ethers 24
Synthesis of Epoxides
• Peroxyacid epoxidation
• Cyclization of Halohydrin
HH
H2O, Cl2
ClH
HO H OH_
ClH
O H_
H H
O
=>
13
Ethers Ethers 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
Ethers Ethers 26
Biosynthesis of Steroids
=>
14
Ethers Ethers 27
Ring Opening in BaseEpoxide’s high ring strain makes it susceptible to nucleophilic
attack.
=>
Ethers Ethers 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. =>
15
Ethers Ethers 29
Orientation of Epoxide Opening
• Base attacks the least hindered carbon.
• In acid, the nucleophile attacks the protonated epoxide at themost 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
Ethers Ethers 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
=>
16
Ethers Ethers 31
Epoxy Resins
Polymer of bisphenol A and epichlorohydrin
HO C
CH3
CH3
OH
bisphenol A
H2C CHCH2Cl
O
epichlorohydrin
=>
Ethers Ethers 32
End of Chapter 14Homework: 33, 35, 37, 39, 40, 42, 45-47
