Electrophilic substitution

In nitration, a hydrogen atom in the benzene ring is replaced by a nitro, -NO₂, group in an electrophilic substitution reaction.

The reaction requires a mixture of concentrated nitric and sulfuric acids and a temperature of 25-60°C. Sulfuric acid acts as a catalyst.

For example, nitrobenzene is produced from the nitration of benzene using HNO₃ and H₂SO₄:

C₆H₆ + HNO₃ ➔ C₆H₅NO₂ + H₂O

Nitrated arenes are important starting materials in the manufacture of dyes and explosives.

In Friedel-Crafts acylation, a hydrogen atom in the benzene ring is replaced by an acyl group in an electrophilic substitution reaction.

The reaction requires an acyl chloride, heat and an AlCl₃ catalyst.

For example, phenylethanone is produced from the acylation of benzene using ethanoyl chloride:

C₆H₆ + CH₃COCl ➔ C₆H₅COCH₃ + HCl

1The carbocation, RCO⁺, is generated: 

RCOCl + AlCl₃ ➔ RCO⁺ + AlCl₄^-

2Benzene undergoes electrophilic substitution with the electrophile RCO⁺:

3The catalyst, AlCl₃ is regenerated:                                                            

H⁺ + AlCl₄^- ➔ AlCl₃ + HCl

1The nitronium ion, NO₂⁺, is generated: 

HNO₃ + H₂SO₄ ➔ NO₂⁺ + HSO₄^- + H₂O

2Benzene undergoes electrophilic substitution with the electrophile NO₂⁺:

3The catalyst, H₂SO₄ is regenerated:                                                          

H⁺ + HSO₄^- ➔ H₂SO₄

Friedel-Crafts reactions are crucial in organic synthesis for carbon-carbon bond formation. These reactions allow for the introduction of acyl groups onto aromatic rings, thereby increasing the number of carbon atoms in the compound and forming new C-C bonds.