Ch_322b_20.09

Ch_322b_20.09 - The Synthesis of Amines by Reduction...

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The Synthesis of Amines by Reduction Methodologies The Reduction of Nitro Compounds Anilines may be prepared by the reduction of nitrobenzenes. The overall synthetic sequence begins with nitration. Ar- H HNO 3 H 2 SO 4 nitration Ar- NO 2 [H] reduction Ar- NH 2 The Dissolving Metal Reduction of Nitrobenzenes to Anilines Zn 2+ + 2e - Zn ! o = -0.76 V Fe 2+ + 2e - Fe ! o = -0.44 V Sn 2+ + 2e - Sn ! o = -0.13 V reduction strength One standard way to reduce nitrobenzenes to anilines is by dissolving metal reductions. These reactions with metals such as iron, zinc and tin typically are carried out at reflux in hydrochloric acid solution, sometimes with acetic acid to help dissolve the aromatic compound. The chemical driving force for these reductions is derived from the favorable potentials for the metal half-cell couples:
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Examples NO 2 nitrobenzene Fe 30% HCl, heat NH 3 + Cl - anilinium chloride HO - H 2 O NH 2 aniline NO 2 p-nitrotoluene Sn HCl, heat CH 3 NH 3 + Cl - CH 3 HO - H 2 O NH 2 p-toluidine
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Ch_322b_20.09 - The Synthesis of Amines by Reduction...

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