In the previous videos on Organic Chemistry, i have discussed about the 3 General Steps involved in Electrophilic Aromatic Substitution Reaction Mechanism and the Halogenation of Benzene. Do check them out if you have missed that. Today, we will look at how Nitration of Benzene proceeds via Electrophilic Substitution Mechanism.
3 Steps in Nitration of Benzene via Electrophilic Substitution Reaction Mechanism:
1: Production of the electrophile (the nitronium ion, NO2+ ion) using conc. H2SO4 and conc. HNO3
Conc. HNO3 acts as a base in the presence of the stronger acid, conc. H2SO4.
The nitronium ion, NO2+ formed is a stronger electrophile.
Equation is HNO3 (base) + 2H2SO4 (acid) → NO2+ (electrophile) + 2HSO4– + H3O+
2: Formation of the carbocation intermediate from the attack of the NO2+ on the benzene ring
This is the slow rate-determining step since it involves the formation of an unstable carbocation intermediate from a stable aromatic compound.
3: Expulsion of H+ ion from the carbocation intermediate to form the aromatic nitrobenzene 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 nitrobenzene from an unstable carbocation intermediate.
Click on the following link for Video on Nitration of Benzene via Electrophilic Aromatic Substitution Reaction Mechanism.
Length of video: 4.25 minutes
For those taking the Singapore’s JC GCE A-Level H2 Chemistry Examination, it is important for you to be able to state the Reagents and Conditions involved in Nitration of Benzene, which are:
- Reagent: Mixture of conc. HNO3 and conc. H2SO4 (Nitration Mixture)
- Conditions: Heat under reflux at 55 degree Celsius
If the temperature rises above 55 degree Celsius, further reaction is possible e.g. 1-3-dinitrobenzene will also be formed.
This is something we always emphasised in our weekly recommended JC A-Level H2 Chemistry Tuition Class.
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 and learn the key H2 Chemistry Concepts together.
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