Transcript silver ring

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An ether has two organic groups (alkyl, aryl, or
vinyl) bonded to the same oxygen atom, R–O–R
Diethyl ether is used industrially as a solvent
Tetrahydrofuran (THF) is a solvent that is a cyclic
ether
Epoxides contain a C-O-C unit which make-up a
three membered ring
Thiols (R–S–H) and sulfides (R–S–R) are sulfur (for
oxygen) analogs of alcohols and ethers
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Ethers are named two ways:

As alkoxy derivatives of alkanes

Derived by listing the two alkyl groups in the
general structure of ROR’ in alphabetical order as
separate words and adding the word ether
 When both alkyl groups are the same, the prefix di-
precedes the name of the alkyl group
 (Ethers can be described as symmetrical or
unsymmetrical)
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CH3CH2 O CH2CH3
Diethyl ether
Ethoxyethane
CH3CH2 O CH3
Ethyl methyl ether
Methoxyethane
CH3CH2 O CH2CH2CH2Cl
3-Chloropropyl ethyl ether
1-Chloro-3-ethoxypropane
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Epoxides (oxiranes)

“epoxy” always preceeds the name of the alkane
O
O
1,2-Epoxycyclohexane
2-Methyl-2,3-epoxybutane
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OCH3
1
O
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O
2
O
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3
O
Br
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O
Cl
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O
Br
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Br
OCH3
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1.
Isopropyl methyl ether
2.
4-t-butoxy-1-cyclohexene
3.
Phenyl propyl ether
4.
O- nitro anisole
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R–O–R ~ tetrahedral bond angle (112° in
dimethyl ether)
Oxygen is sp3-hybridized
Oxygen atom gives ethers a slight dipole
moment (diethyl ether 1.2 D)
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CH3CH2OCH2CH3
Diethyl ether
bp =35oC
solubility in water: 7.5 g/100mL
CH3CH2CH2CH2CH3
Pentane
bp =36oC
solubility in water: insoluble
CH3CH2CH2CH2OH
1-Butanol
bp =117oC
solubility in water: 9 g/100mL
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Acid catalyzed synthesis of ethers:
2
OH
butanol
H2SO4
O
130oC
Dibutyl ether
+ H2O
Limited to symmetrical ethers. WHY?
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HCl
2
OH
O
+
130 C
H
OH
H O
H3 O+
+
Cl-
H
O
H
O+
H---Cl
H
+
H3O+
+
H
O+
-
Cl
O
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
Williamson ether synthesis
•Metal alkoxides react with primary alkyl halides by an
SN2 pathway to yield ethers.
•Secondary and tertiary substrates react following an
E2 mechanism
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OH
O – Na+
NaH
O
THF
+
CH3CH2----I
+
H2
+
NaI
THF
O
H
O– Na+
THF
+
Na+ H-
CH3CH2----I
+
H2
O
NaI
+
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O
CH3CH2O
+ CH3CH2Br
+
Br
SN2
E2
?
?
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How would you prepare the following
compounds using a Williamson synthesis?
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Methyl propyl ether
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Anisole (methyl phenyl ether)
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Br
O
+ CH3CH2CHCH3
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React alkene with an alcohol and mercuric
acetate or trifluoroacetate
Demercuration with NaBH4 yields an ether
Overall Markovnikov addition of alcohol to
alkene
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Ethers are generally unreactive
Strong acid will cleave an ether at elevated
temperature
HI, HBr produce an alkyl halide from less
hindered component by SN2 (tertiary ethers
undergo SN1)
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Note that the halide attacks the protonated ether at
the less highly substituted site.
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Specific to allyl aryl ethers, ArOCH2CH=CH2
Heating to 200–250°C leads to an o-allylphenol
Result is alkylation of the phenol in an ortho position
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Concerted pericyclic 6-electron, 6-membered
ring transition state
Mechanism consistent with 14C labeling
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Cyclic ethers behave like acyclic ethers, except
if ring is 3-membered
Dioxane and tetrahydrofuran are used as
solvents
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Three membered ring ether is called an
oxirane (root “ir” from “tri” for 3-membered;
prefix “ox” for oxygen; “ane” for saturated)
Also called epoxides
Ethylene oxide (oxirane; 1,2-epoxyethane) is
industrially important as an intermediate
Prepared by reaction of ethylene with oxygen
at 300 °C and silver oxide catalyst
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Treat an alkene with a peroxyacid
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peroxyacetic acid
H
C6H5
H
O
O
+
H5C6
H
(E)-1,2-diphenylethene
O
H
CH3
C6H5
O
H5C6
OH
+
O
H
trans-1,2-diphenyloxirane
CH3
acetic acid
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Addition of HO-X to an alkene gives a halohydrin
Treatment of a halohydrin with base gives an epoxide
Intramolecular Williamson ether synthesis
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Water adds to epoxides with dilute acid at
room temperature
Product is a 1,2-diol (on adjacent C’s: vicinal)
Mechanism: acid protonates oxygen and water
adds to opposite side (anti-addition)
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1,2-ethanediol from acid catalyzed hydration of
ethylene
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Widely used as automobile antifreeze (lowers freezing
point of water solutions)
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Anhydrous HF, HBr, HCl, or HI combines with
an epoxide
Gives trans product
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Strain of the three-membered ring is relieved on
ring-opening
Hydroxide cleaves epoxides at elevated
temperatures to give trans 1,2-diols
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Complete the reaction
O
CH2
OH-
H2O, 100oC
Methylenecyclohexane
oxide
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O
-
CH2
OH
O–
CH 2OH
H
O
H
OH
CH 2OH
+
-
OH
100 C
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Adds –CH2CH2OH to the Grignard reagent’s hydrocarbon
chain
Acyclic and other larger ring ethers do not react
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Thiols (RSH), are sulfur analogs of alcohols
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Named with the suffix -thiol
SH group is called “mercapto group”
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1
SH
2
SH
Br
3
SH
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1.
Cyclopentanethiol
2.
3-methyl-4-heptanethiol
3.
4-ethyl-4-isopropyl-2-methyl-3-hexanethiol
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Sulfides (RSR), are sulfur analogs of ethers

Named by rules used for ethers, with sulfide in
place of ether for simple compounds and alkylthio
in place of alkoxy
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1
2
3
4
S
S
ethyl phenyl sulfide
sec-butyl isopropyl sulfide
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From alkyl halides by displacement with a
sulfur nucleophile such as SH
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The alkylthiol product can undergo further
reaction with the alkyl halide to give a
symmetrical sulfide, giving a poorer yield of the
thiol
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Thiolates (RS) are formed by the reaction of a thiol
with a base
Thiolates react with primary or secondary alkyl halide
to give sulfides (RSR’)
Thiolates are excellent nucleophiles and react with
many electrophiles
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