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LECTURE 7

Dr Ali El-Agamey

CHEM-103:

BASIC ORGANIC CHEMISTRY

DAMIETTA UNIVERSITY

Electrophilic aromatic substitution

2

Butadiene p158a

Hexatriene p156a

3

Hexatriene p156b

p163c

4

p163d

p159c

5

p155b

Benzene p154a

6

Benzene p154b

Benzene p154c

7

p154d

Benzene p154e

8

15

Resonance Energy

9

Electrophilic aromatic substitution

Electrophilic aromatic substitution

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Electrophilic aromatic substitution

Electrophilic aromatic substitution

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21

Bromination of Benzene

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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)

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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

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Energy Diagram for Bromination

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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

+).

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Chapter 17 27

Mechanism for the Nitration of Benzene

Nitration

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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

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Sulfonation

Sulfonation

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Friedel Craft’s Alkylation

Chapter 17 34

Mechanism of the Friedel–Crafts Reaction

Step 1

Step 2

Step 3

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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.

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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.

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Electrophilic aromatic substitution

p555a

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Electrophilic Aromatic Substitution

(1) Nitration

(2) Sulfonation (3) Halogenation

(4) Friedel-Crafts Alkylation

(5) Friedel-Crafts Acylation

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Homework: Complete the following scheme

(1) (2)

(3)

(4) (5)

(6) (7)

(8) (9)

(10) (11)

(12)