LSW S04
212 Exam 2
Aromatic Ring Reactions
Electrophilic Aromatic Substitution:
E
+
E
+
+
H+
Basic mechanism:
1.
2.
3.


4.
E+ +
Resonance stabilization:
Why Substitution not Addition?
E
E
E+ +
NOT E+ +
240
LSW S04
212 Exam 2
Reactions and Reagents:
Reaction
Reagents
HNO3 / H2SO4
Electrophile
Product
NO2
H2SO4 or SO3 /
H2SO4
SO3H
Cl2 / Fe or
FeCl3
Cl
Br2 / Fe or
FeBr3
Br
R-Cl / AlCl3
R-OH / H+
C=C / H+
R
O
RCOCl / AlCl3
RCO2COR /
AlCl3
R
241
LSW S04
212 Exam 2
Nitration of Benzene
NO2
H2SO4
HNO3 +
+
Heat
H2O
Reaction type:
Reagents:
Electrophilic species:
Mechanism:
Formation of the electrophile:
O
O S OH
O
HO NO2 + H
H
H O
+
O
O S OH
O
H
+ O N O
H O
Electrophilic aromatic substitution:
O
N
O
O
N
O
O
H3O
+
O
N
O
H
242
H
NO2
LSW S04
212 Exam 2
Sulfonation of Benzene
SO3H
H2SO4 +
H2O
+
Heat
Reaction type:
Reagent:
Electrophilic species:
Mechanism:
Electrophilic aromatic substitution:
O
O
S
O
H O
O S OH
O
+
O
HO S
O
O
O
S
O
O
Protonation:
O
O
S
O
+
H O
O S OH
O
O
O
243
O H
S
+
O
O S OH
O
LSW S04
212 Exam 2
Halogenation of Benzene
X2
X
Fe
Heat
X = Br or Cl
+
+
HX
Reaction type:
Reagents:
Electrophilic species:
Limitations:
Mechanism:
Formation of the electrophile:
Br
Br + FeBr3
Br
Br
Electrophilic Aromatic Substitution:
Br
Br
FeBr3
Br
HBr + FeBr3
+
Br
244
FeBr3
FeBr3
LSW S04
212 Exam 2
Friedel-Crafts Alkylation of Benzene
R
AlCl3
RCl +
+
HCl
Reaction type:
Reagents:
Electrophilic species:
Limitations:
H
H
H
H
Cl
AlCl3
H
H
H
H
H
+
H
AlCl4
Alkyl:
Arenes:
Multiple alkylation:
Mechanism:
Formation of the electrophile:
(CH3)3C Cl + AlCl3
(CH3)3C
+
Cl AlCl3
Electrophilic Aromatic Substitution:
+ HCl
(CH3)3C
C(CH3)3
+ AlCl3
245
LSW S04
212 Exam 2
Friedel-Crafts Acylation of Benzene
O
O
AlCl3
R
+ RCCl
+
HCl
Reaction type:
Reagents :
Electrophilic species:
H2CC
H2CC
O
O
Limitations:
Advantages:
Mechanism:
Formation of the electrophile:
O
O
RC Cl + AlCl3
RC
+
Cl AlCl3
Electrophilic Aromatic Substitution:
Cl AlCl3
O
RC
246
O
CR
LSW S04
212 Exam 2
Alkylation via Acylation and reduction:
O
H
O
[R]
AlCl3
+ RCCl
+
R
HCl Reducing
Agent
Reaction type:
Reagents :
Clemmensen Reduction (acidic conditions)
Wolff-Kishner Reduction (basic conditions)
Which one?
Limitations:
Advantages:

CH3CH2COCl
AlCl3
ACYLATION
REDUCTION
ALKYLATION
AlCl3
CH3CH2CH2Cl
247
H
R