Chapter 15 Reactions of
Aromatic Compounds
ORGANIC CHEMISTRY
Chapter 15
15.1 Electrophilic Aromatic Substitution
Reaction
Department of Chemistry, Xiamen University
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Chapter 15
The most characteristic reactions of benzenoid arenes
are the substitution reactions that occur when they
react with electrophilic reagents.
The electrophiles are either a positive ion (E+) or some
other electron-deficient species with a large partial
positive charge.
E
+
E Nu
+ H Nu
Electrophilic aromatic substitution (EAS)
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
X2, FeX3
X
+ HX
(X=Cl, Br)
HNO3
H2SO4
SO3
NO2
+ H2O
Halogenation
Nitration
SO3H
Sulfonation
H2SO4
RCl, AlCl3
(R can rearrange)
RCOCl, AlCl3
R
+ HCl
O
C R
+ HCl
Friedel-Crafts
Reaction
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
15.2 A General Mechanism for
Electrophilic Aromatic Substitution:
Arenium Ions
Department of Chemistry, Xiamen University
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Chapter 15
+ E Nu
E
E
E
H
H
H
Arenium ion
E (σ complex)
H
E
H
H
E
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ORGANIC CHEMISTRY
Chapter 15
15.3 Halogenation of Benzene
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
+ X2
X
FeX3 or Fe
+ HX
Reactivity F2 > Cl2 > Br2 > I2
+ Cl2
FeCl3 or Fe
Cl
+ HCl
25°C
Chlorobenzene
(90%)
+ Br2
FeBr3 or Fe
Br
+ HBr
Bromobenzene
(75%)
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
Mechanism
Br2 + Fe
Br
Br
FeBr3
+ FeBr3
Br + Br
+ Br
Br
Br FeBr3
FeBr3
Br
H
Br
H
Br
+ HBr
FeBr3
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
15.4 Nitration of Benzene
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
NO2
HNO3
H2O
H2SO4
50 ~ 55
(85
H2O NO2 + HSO4
HONO2 + H2SO4
H2O NO2 + H2SO4
+ NO2
)
H3O + NO2 + HSO4
NO2
H
H
NO2
σ−complex
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
15.5 Sulfonation of Benzene
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 15
+ H2SO4-SO3
25
or conc. H2SO4 / 75
O δ−
+
O
S
SO3H
Benzenesulfonic acid
苯磺酸
SO3
H
H
δ+ O
SO3
SO3H
+ H+
SO3H
H2SO4
+ H2 O
+ H2SO4
Department of Chemistry, Xiamen University