Reactions of Benzene

Benzene, an aromatic hydrocarbon, undergoes substitution reactions rather than addition reactions due to the stability provided by its conjugated pi electron system, forming a stable delocalised ring.
Electrophilic substitution is the primary reaction type of benzene rings. An electrophile replaces a hydrogen atom on the benzene ring, maintaining the ring’s aromaticity.
A general mechanism for electrophilic substitution in benzene involves three primary steps: generation of the electrophile, attack of the electrophile, and deprotonation to regenerate the benzene ring.
The nitration of benzene, a method of introducing a nitro group (-NO2), entails the action of concentrated nitric acid and concentrated sulfuric acid, yielding nitrobenzene.
Sulfonation of benzene uses sulfuric acid or oleum at high temperature, forming a benzene-sulfonic acid. Sulfonation is reversible and can be withdrawn by adding steam.
Halogenation of benzene involves replacing one hydrogen atom with a halogen atom. Halogen carriers like FeBr3 or AlCl3 are used to generate the electrophile.
The Friedel-Crafts alkylation and acylation reactions introduce alkyl and acyl groups onto benzene rings, respectively. Both reactions require a Lewis acid as a catalyst, commonly aluminium chloride (AlCl3) or Iron(III) Chloride (FeCl3).
Importantly, Friedel-Crafts reactions can fail or give unexpected results with certain electrophiles. This reaction will fail when the electrophile is deactivated, such as in the case of a valuable or aromatic amines.
In Friedel-Crafts acylation, the acyl chloride (RCOCl) or acid anhydride (RCOOCR’) acts as the electrophile to form a phenyl ketone.
Benzene reactions require particular caution due to the creation of toxic or carcinogenic byproducts. Always follow safety guidelines and use appropriate personal protective equipment.

Remember, these reactions usually take place under specific conditions using catalysts and temperatures to optimise yield. Understanding the nuances of these reactions is necessary to predict and control chemical behaviour effectively.