Transcript 23.11 Synthesis of Amines

Aromatic Amines
• Recall:
• The amino group is a powerful activating group that
directs ortho and para
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Reduction of Nitro Compounds
• Catalytic hydrogenation:
• Reduction with finely divided metal powders:
23.11 Synthesis of Amines
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Reduction of Nitro Compounds
• LiAlH4 and NaBH4 fail to provide the amine
23.11 Synthesis of Amines
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Problems
• Draw the products for the following reactions:
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Reductive Amination
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• Sodium cyanoborohydride, NaBH3CN and sodium
triacetoxyborohydride, NaBH(OAc)3, are common choices in
the lab for the reduction step
• Formaldehyde can be used to introduce methyl groups
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23.7 Alkylation and Acylation Reactions of Amines
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Problem
• Draw the complete mechanism for the following problem:
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Hofmann and Curtius Rearrangements
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The Hofmann Rearrangement
• Sometimes called the Hofmann hypobromite reaction
• Cl2 is sometimes used in place of Br2
• A primary amide is the required starting compound
23.11 Synthesis of Amines
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The Curtius Rearrangement
• Acyl azides provide access to primary amines via an isocyanate
• Concerted reaction
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The Curtius Rearrangement
• The resulting isocyanate can be hydrated in
acid or base
• Carbamic acids spontaneously decarboxylate
23.11 Synthesis of Amines
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Hofmann vs. Curtius
• In the Hofmann rearrangement, the isocyanate cannot be
isolated as the reaction is carried out in aqueous base
23.11 Synthesis of Amines
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Curtius and Hofmann Rearrangements
• In both of these reactions, the alkyl group migrates
with complete retention of configuration
23.11 Synthesis of Amines
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Problems
• Draw the mechanisms for the following rxns
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Acylation of Amines
• Amines can be converted into amides by reaction with acid
chlorides, anhydrides, or esters.
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• See section 21.8 for review of these rxns
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