Transcript Chapter 16 Ethers, Epoxides, and Sulfides

Ethers and Thioethers
Bond angles at oxygen are sensitive
to steric effects
O
O
H
H
105°
108.5°
O
O
CH3
CH3
112°
H
CH3
C(CH3)3
(CH3)3C
132°
Functional Class IUPAC Names of Ethers
name the groups attached to oxygen in
alphabetical order as separate words; "ether" is
last word
CH3OCH2 CH3
ethyl methyl ether
CH3CH2OCH2CH2CH2Cl
3-chloropropyl ethyl ether
CH3CH2OCH2 CH3
diethyl ether
Substitutive IUPAC Names of Ethers
name as alkoxy derivatives of alkanes
CH3OCH2 CH3
methoxyethane
CH3CH2OCH2CH2CH2Cl
1-chloro-3-ethoxypropane
CH3CH2OCH2 CH3
ethoxyethane
An oxygen atom affects geometry in much the
same way as a CH2 group
most stable conformation of diethyl ether
resembles pentane
An oxygen atom affects geometry in much the
same way as a CH2 group
most stable conformation of tetrahydropyran
resembles cyclohexane
PREPARATION
CH3CH2CH2CH2ONa + CH3CH2I
CH3CH2CH2CH2OCH2CH3 + NaI
(71%)
Ethers resemble alkanes more than alcohols
with respect to boiling point
boiling point
36°C
35°C
O
OH
117°C
Intermolecular hydrogen
bonding possible in
alcohols; not possible
in alkanes or ethers.
Ethers resemble alcohols more than alkanes
with respect to solubility in water
solubility in water (g/100 mL)
very small
7.5
O
OH
9
Hydrogen bonding to
water possible for ethers
and alcohols; not
possible for alkanes.
Summary of reactions of ethers
. Ethers are relatively unreactive.
Their low level of reactivity is one reason why
ethers are often used as solvents in chemical
reactions.
Ethers oxidize in air to form explosive
hydroperoxides and peroxides.
REACTIONS
CH3CHCH2CH3 HBr
OCH3
heat
CH3CHCH2CH3 + CH3Br
Br
H
(81%)
H
H
CH3OCH3
H+
CH3O+CH3
H
Substitutive IUPAC Names of Sulfides
name as alkylthio derivatives of alkanes
CH3SCH2 CH3
methylthioethane
SCH3
(methylthio)cyclopentane
CH3CH2SCH2 CH3
ethylthioethane
Functional Class IUPAC Names of Sulfides
analogous to ethers, but replace “ether” as last
word in the name by “sulfide.”
CH3SCH2 CH3
ethyl methyl sulfide
CH3CH2SCH2 CH3
diethyl sulfide
SCH3
cyclopentyl methyl sulfide
Preparation of RSR'
prepared by nucleophilic substitution (SN2)
–
S ••
••
R
••
CH3CHCH
+
CH2
R'
X
NaSCH3
R
••
S
••
R'
CH3CHCH
methanol
Cl
SCH3
CH2
R
••
S
••
R'
Oxidation of RSR'
•• –
•• O ••
+
R S R'
••
•• –
•• O ••
R
++
S R'
• O ••
•
•• –
sulfide
sulfoxide
sulfone
either the sulfoxide or the sulfone can be isolated
depending on the oxidizing agent and reaction
conditions
Sulfides can act as nucleophiles
R
••
S ••
R'
+
R"
X
R
+
••
S
R'
product is a sulfonium salt
R"
X–