Organic Chemistry Nitro Group Reduction

Reaction of Nitro Group

• Nitro group can be reduced by catalytic or chemical reduction methods.

Catalytic Reduction

• Nitro group can be reduced to an amino group by using hydrogen gas and a catalyst like nickel, platinum, or palladium.

Chemical Reduction

• The reduction product of a nitro group depends on the strength of the reducing agent and the pH of the medium.

Reduction in Acidic Medium

• In acidic medium, nitro group is reduced to an amino group using a strong reducing agent like iron, tin, or zinc with hydrochloric acid or SnCl2.

Reduction in Neutral Medium

• In neutral medium, nitro group is reduced to N-phenyl hydroxylamine using zinc with ammonium chloride.

Reduction in Alkaline Medium

• In alkaline medium, nitro group can be reduced to different products depending on the reducing agent and the reaction conditions.
• Using NaOH/CH3OH, a nitro group can be reduced to an azoxybenzene.
• Using SnCl2/NaOH, it can be further reduced to an azobenzene.
• Using Zn/HCl, it forms an azobenzene.
• Using Zn/NaOH, a hydrazobenzene can be formed.
• Using SnCl2/HCl, it is reduced to corresponding amine.

Reactions of Aromatic Nitro Compounds

• Aromatic nitro compounds undergo reactions involving the benzene ring or the nitro group.

Reactions of Benzene Ring

• Aromatic nitro compounds undergo electrophilic aromatic substitution (EAS) reactions, but the nitro group deactivates the ring and directs the incoming electrophile to the meta position.

• The nitro group is electron-withdrawing and meta-directing, restricting the ring's reactivity towards electrophilic aromatic substitution such as Friedel-Crafts alkylation or acylation.

• Nitro groups activate the ring toward nucleophilic aromatic substitution reactions. This activation occurs due to the electron-withdrawing and resonance effects of the nitro group, making it an excellent leaving group.

• The nitro group directs incoming nucleophiles to the ortho and para positions.

• Nucleophilic aromatic substitution reactions typically involve a "Meisenheimer intermediate" which is stabilized by the nitro group.

• There are three main categories of nucleophilic aromatic substitution reactions:

  • Substitution of hydride at the ortho and para positions to nitro group.
  • Substitution of halide at the ortho or para position to nitro group.
  • Substitution of nitro group if multiple nitro groups are at ortho or para positions to each other.

Reactions of Nitro Group

• The nitro group can undergo reactions like reduction or participate in the reactions of the benzene ring, such as EAS or SNAr.