The main reactions which benzene will undergo include the replacement of one of the 6 hydrogen atoms from the benzene ring
This is different to the reactions of unsaturated alkenes, which involve the double bond breaking and the electrophile atoms 'adding on' to the carbon atoms
These reactions where at least one of the H atoms from benzene are replaced, are called electrophilic substitution reactions
The hydrogen atom is substituted by the electrophile
You must be able to provide the mechanisms for specific examples of the electrophilic substitution of benzene
General Electrophilic Substitution Mechanism:
The delocalised π system is extremely stable and is a region of high electron density
Electrophilic substitution reactions involve an electrophile, which is either a positive ion or the positive end of a polar molecule
There are numerous electrophiles which can react with benzene
However, they usually cannot simply be added to the reaction mixture to then react with benzene
The electrophile has to be produced in situ, by adding appropriate reagents to the reaction mixture
The electrophilic substitution reaction in arenes consists of three steps:
Generation of an electrophile
Electrophilic attack
Regenerating aromaticity
Nitration of benzene mechanism
In the first step, the electrophile is generated
The electrophile NO2+ ion is generated by reacting concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4)
Halogenation of benzene mechanism
Benzene will undergo a substitution reaction with a halogen if a metal halide carrier is present
This generates the electrophile for the reaction to occur
The different stages in the chlorination of benzene
Friedel-Crafts acylation mechanism
In the Friedel-Crafts acylation reaction, an acyl group is substituted into the benzene ring
An acyl group is an alkyl group containing a carbonyl, C=O group