Electrophilic Substitution Reactions Of Benzene Flashcards
What type of reactions do benzene and its derivatives undergo?
Benzene and its derivatives undergo substitution reactions.
In substitution reactions of benzene, what is replaced on the benzene ring?
A hydrogen atom is replaced by another atom or group of atoms.
Benzene typically reacts with _______.
[electrophiles]
Most of the reactions of benzene proceed by _______ substitution.
[electrophilic]
What is formed when benzene reacts with nitric acid?
Nitrobenzene.
What catalyst is used in the nitration of benzene?
Sulfuric acid.
At what temperature is the nitration of benzene typically maintained for a good reaction rate?
50°C.
What happens if the temperature of the nitration reaction rises above 50°C?
Further substitution reactions may occur, leading to the production of dinitrobenzene.
Why is temperature control important in the preparation of organic compounds?
To prevent further substitution reactions.
What is nitrobenzene used for?
Preparation of dyes, pharmaceuticals, and pesticides
Nitrobenzene can also be a starting material for the preparation of paracetamol.
What is the mechanism for the nitration of benzene?
Electrophilic substitution
The electrophile in this reaction is the nitronium ion, NO₂⁺.
What produces the nitronium ion in the nitration of benzene?
Reaction of concentrated nitric acid with concentrated sulfuric acid
This occurs in Step 1 of the nitration mechanism.
What happens in Step 2 of the nitration mechanism?
The nitronium ion accepts a pair of electrons from the benzene ring to form a dative covalent bond.
This forms an unstable organic intermediate.
What is formed when the unstable organic intermediate breaks down in the nitration of benzene?
Nitrobenzene and H⁺ ion
A stable benzene ring is reformed in this step.
What regenerates the catalyst in the nitration mechanism?
The H⁺ ion reacts with the HSO₄⁻ ion.
This occurs in Step 3 of the mechanism.
What is required for the halogenation of benzene?
A catalyst called a halogen carrier
Common halogen carriers include AlCl₃, FeCl₃, AlBr₃, and FeBr₃.
What is the electrophile in the bromination of benzene?
Bromonium ion, Br⁺
It is generated when the halogen carrier reacts with bromine.
What occurs during Step 2 of the bromination mechanism?
The bromonium ion accepts a pair of electrons from the benzene ring to form a dative covalent bond.
This results in an unstable organic intermediate.
What is the product formed after the breakdown of the organic intermediate in bromination?
Bromobenzene and H⁺ ion
The H⁺ ion reacts with the FeBr₄⁻ ion to regenerate the catalyst.
What is the mechanism for the chlorination of benzene?
Electrophilic substitution
The halogen carrier used can be FeCl₃, AlCl₃, or iron metal and chlorine.
How does benzene react with bromine without a halogen carrier?
Benzene does not react with bromine unless a halogen carrier is present.
This is due to benzene’s stability and electron delocalization.
What is the reason benzene does not react with non-polar bromine?
Insufficient π-electron density to polarize the bromine molecule.
This prevents a reaction from taking place.
What is the difference between the reaction mechanisms of alkenes and benzene with bromine?
Alkenes undergo electrophilic addition, while benzene undergoes electrophilic substitution.
Benzene’s delocalized electrons lead to different reactivity.
