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1
LECTURE 7
Dr Ali El-Agamey
CHEM-103:
BASIC ORGANIC CHEMISTRY
DAMIETTA UNIVERSITY
Electrophilic aromatic substitution
11
21
Bromination of Benzene
22
Mechanism for the Bromination of Benzene: Step 1
• Before the electrophilic aromatic substitution can take place, the electrophile must be activated.
• A strong Lewis acid catalyst, such as FeBr3, should be used.
B r B r F e B r 3 B r B r F e B r 3 + -
(stronger electrophile than Br2)
12
23
Step 2: Electrophilic attack and formation of the sigma complex.
Step 3: Loss of a proton to give the products.
Mechanism for the Bromination of Benzene: Steps 2 and 3
24
Energy Diagram for Bromination
13
Nitration
Chapter 17 26
Nitration of Benzene
• Sulfuric acid acts as a catalyst, allowing the reaction to be faster and at lower temperatures.
• HNO3 and H2SO4 react together to form the electrophile of the reaction: nitronium ion (NO2
+).
15
Chapter 17 29
Reduction of the Nitro Group
• Treatment with zinc, tin, or iron in dilute acid will reduce the nitro to an amino group.
• This is the best method for adding an amino group to the ring.
Sulfonation
17
Friedel Craft’s Alkylation
Chapter 17 34
Mechanism of the Friedel–Crafts Reaction
Step 1
Step 2
Step 3
18
Alkylation
Chapter 17 36
Side-Chain Oxidation
• Alkylbenzenes are oxidized to benzoic acid by heating in basic KMnO4 or heating in Na2Cr2O7/H2SO4.
• The benzylic carbon will be oxidized to the carboxylic acid.
19
Friedel Craft’s Acylation
Chapter 17 38
Clemmensen Reduction
• The Clemmensen reduction is a way to convert acylbenzenes to alkylbenzenes by treatment with aqueous HCl and amalgamated zinc.