Nitrobenzene : Laboratory preparation, Properties and Uses.

Laboratory Preparation of Nitrobenzene :

It is prepared in lab by heating benzene with conc. HNO₃ and conc. H₂SO₄ at 60⁰C.

Procedure :

50 ml of benzene is taken in a round bottomed flask. To this flask, 60 ml conc. HNO₃ and 60 ml conc. H₂SO₄ (i.e. nitrating mixture) is added a little at a time, shaking and cooling after each addition. Then the mixture is heated (refluxed) in water bath at 60⁰C for about one and half hour till the yellow oily layer appears on the surface. The flask is then cooled and the layer of nitrobenzene is separated by using separating funnel.

Purification :

It is first washed with dil. Na₂CO₃ to remove the acidic impurities and then with water severaltimes. It is then dried over fused calcium chloride. It is finally distilled at 211⁰C to get pure nitrobenzene.

Physical Properties of Nitrobenzene :

• It is pale yellow oily liquid having bitter almond smell.
• It is insoluble in water but soluble in organic solvent.
• It’s boiling point is 210⁰C.

Chemical Properties of Nitrobenzene :

A ) Reduction of nitrobenzene in different medium :

Nitrobenzene gives different products in different medium by using different reducing agent.

• Reduction of nitrobenzene in acidic medium :

Nitrobenzene on reduction with Zn/HCl or Sn/ HCl gives aniline.

• Catalytic reduction of nitrobenzene :

Nitrobenzene when reduced by hydrogen in presence of nickel or platinum as a catalyst gives aniline.

• Reduction of nitrobenzene in neutral medium :

Nitrobenzene on reduction with Zn and aq. NH₄Cl gives phenyl hydroxylamine.

• Reduction of nitrobenzene with LiAlH₄ :

Lithium aluminium hydride reduces nitrobenzene to azobenzene.

• Reduction of nitrobenzene in alkaline (basic) medium :

• Electrolytic reduction of nitrobenzene :

Nitrobenzene when reduced electrolytically, first gives phenyl hydroxylamine which immediately rearrenges to give p- aminophenol.

B) Reactions of nitrobenzene due to benzene ring :

NO₂ group is electron withdrawing group. It withdraws ∏- electrons from benzene ring, decreasing electron density of aromatic ring.

From the above resonating structures, it is clear that electron density is comparatively high at meta position. Thus incoming electrophile attacks at meta position to give meta substituted product. Thus –NO₂ is meta directing group.

Electrophilic substitution reactions of nitrobenzene :

Uses of Nitrobenzene :

• For the manufacture of aniline.
• For making shoe polishes.
• As an oxidizing agent in organic synthesis.
• For scenting cheap soaps.

References :

• Bahl, B.S., A., Advanced Organic Chemistry, S. Chand and company Ltd, New Delhi, 1992.
• Finar, I. L., Organic Chemistry, Vol. I and Vol. II, Prentice Hall, London, 1995.
• Ghosh, S.K., Advanced General Organic Chemistry, Second Edition, New Central Book Agency Pvt. Ltd., Kolkata, 2007.