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You are here: Home / Organic Chemistry Arenes / Organic Chemistry: Halogenation of Benzene via Electrophilic Aromatic Substitution

Organic Chemistry: Halogenation of Benzene via Electrophilic Aromatic Substitution

April 16, 2018 By Sean Chua Leave a Comment

Halogenation of Benzene - H2 Chemistry Tuition
Credit: IIIegalsocks

In the previous video on JC2 A-Level H2 Chemistry Organic Chemistry, i have discussed about the stability of an aromatic ring and the 3 Steps involved in Electrophilic Aromatic Substitution Reaction Mechanism. Do check them out if you have missed that.

Today, we will take a look at how Halogenation of Benzene proceeds via Electrophilic Aromatic Substitution Mechanism.

The example i am going to use will be Chlorination of Benzene, which involves the following three steps:

Step 1: Production of the electrophile, Cl+ ion, from Cl2 and a Lewis Acid Catalyst (also known as Halogen Carrier) e.g. AlCl3

Common Lewis Acid Catalysts are AlCl3, AlBr3, FeCl3, FeBr3, Fe, Al

Step 2: Formation of the carbocation intermediate from the attack of the Cl+ on the benzene ring

This is the slow rate-determining step since it involves the formation of unstable carbocation intermediate from a stable aromatic compound

Step 3: Expulsion of H+ ion from the carbocation intermediate to form the aromatic chlorobenzene and the delocalised pi (π) system is preserved i.e. benzene ring is re-formed

This is the fast step since it involves the formation of stable aromatic chlorobenzene from an unstable carbocation intermediate

Click on the following link for Video on Halogenation of Benzene via Electrophilic Aromatic Substitution Reaction Mechanism.

H2 Chemistry Video on Halogenation of Benzene via Electrophilic Aromatic Substitution Reaction Mechanism

Length of video: 6.25 minutes

Similarly, Bromination of Benzene will be carried out in a same way. Benzene reacts with Br2 in the presence of FeBr3 to give bromobenzene and steamy white fumes of HBr can be detected. This is another common A-Level H2 Chemistry examination question when it comes to halogenation of benzene.

Jim Clark from chemguide.co.uk has also written a short and concise blog post on Halogenation of Benzene. I have recommended students from my weekly JC A-Level H2 Chemistry tuition classes to take a look.

In the next video on Organic Chemistry, we will take a look at another common reaction (in Singapore’s JC GCE A-Level H2 Chemistry) involving Electrophilic Substitution Reaction Mechanism of Arenes, namely: Nitration – Substitution reactions with a Nitration Mixture i.e. Conc. H2SO4 and Conc. HNO3.

I hope you find the content easy for your understanding and if you have any questions, leave me a comment below. Feel free to share this blog post with your friends.

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PS: Under related articles below, there are several blog post discussions and questions related to Electrophilic Substitution Reactions in Organic Chemistry. You can also do a keyword search using the search box at the top right hand corner.

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Related Articles:

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  • Organic Chemistry: Markovnikov’s Rule in Electrophilic Addition of Unsymmetrical Alkenes Video
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Sean Chua
Sean Chua
Winners Education Centre Pte. Ltd.
Many know me as the Ten Year Series book author for JC A-Level H2 Chemistry and O-Level Pure Chemistry. My 19+ years of coaching experience (since 1999) with more than 1500 students from 180+ JCs and Secondary Schools has allowed me to understand the true reasons why students are not able to perform well in Chemistry. Most importantly, my strength lies in using everyday analogies (even grandmothers can understand!) to simplify abstract concepts. Also, my teaching methodology has been designed to be fun, enjoyable and effective for my students.

If you want to have an enjoyable time learning Chemistry and being motivated to excel in Chemistry, contact me today at 9828 7357

Filed Under: Organic Chemistry Arenes Tagged With: Aromatic Compounds, Electrophilic Substitution, Halogen Carrier, Halogenation, Lewis Acid Catalysts, Organic Chemistry Arenes

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