Electrophilic Aromatic Substitution of Benzene with Mechanism and Examples

What is Electrophilic Substitution of Benzene?

Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft’s alkylation and acylation, etc.

The Mechanism for Electrophilic Substitution of Benzene

An electrophilic substitution reaction generally involves three steps:

1. Generation of electrophile: In the presence of Lewis acid, generation of electrophile takes place. As the Lewis acid accepts the electron pair from the attacking reagent.

Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft’s alkylation and acylation, etc.

2. Formation of arenium ion: The electrophile generated attacks on the benzene ring to form a positively charged cyclohexadienyl cation better called an arenium ion containing one sp3 hybridized carbon atom. The positive charge is effectively distributed over three carbon atoms by resonance which makes it partially stable.

Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft’s alkylation and acylation, etc.

As the delocalization of electrons stops at an sp3 hybridized carbon atom, the arenium ion is not aromatic in nature.

3. Removal of positive charge from the carbocation intermediate: The arenium ion finally loses its proton from sp3 hybridized carbon to a Lewis base restoring the aromaticity.

Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft’s alkylation and acylation, etc.

Few examples of electrophilic aromatic substitution

1. Nitration of Benzene

Benzene reacts with nitric acid at 323-333k in presence of sulphuric acid to form nitrobenzene. This reaction is known as nitration of Benzene.

Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft’s alkylation and acylation, etc.

2. Sulphonation of Benzene

Sulphonation of benzene is a process of heating benzene with fuming sulphuric acid (H2SO4 +SO3) to produce benzenesulphonic acid. The reaction is reversible in nature.

Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft’s alkylation and acylation, etc.

3. Halogenation of Benzene

Benzene reacts with halogens in the presence of Lewis acid like FeCl3, FeBr3 to form aryl halides. This reaction is termed halogenation of benzene.

Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft’s alkylation and acylation, etc.

Frequently Asked Questions – FAQs

Q1

Why does benzene undergo electrophilic substitution?

Benzene is a planar molecule which has delocalized electrons above and below the plane of the ring. Being electron-rich, it is highly attractive to electron-deficient species i.e., electrophiles.

Q2

What are the three steps involved in the electrophilic substitution of benzene?

Step 1: Generation of electrophile.
Step 2: Formation of the carbocation.
Step 3: Removal of the proton.

Q3

What is an electrophilic substitution reaction? Give example

In electrophilic aromatic substitution reactions, an atom attached to an aromatic ring is replaced with an electrophile.
Examples of such reactions include aromatic nitrations, aromatic sulphonation, and Friedel-Crafts reactions

Q4

What are the products of nitration, chlorination and Friedel Craft alkylation of benzene ?

Nitrobenzene, chlorobenzene and methyl benzene respectively are the products of nitration, chlorination and Friedel Craft alkylation of benzene.

Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations. In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS". He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.