Nucleophilic Aromatic Substitution Reactions
Some typical substitution reactions on arenes are listed below.
- In the Bamberger rearrangement N-phenylhydroxylamines rearrange to 4-aminophenols. The nucleophile is water.
- In the Sandmeyer reaction and the Gattermann reaction diazonium salts react with halides.
- The Smiles rearrangement is the intramolecular version of this reaction type.
Nucleophilic aromatic substitution is not limited to arenes, however; the reaction takes place even more readily with heteroarenes. Pyridines are especially reactive when substituted in the aromatic ortho position or aromatic para position because then the negative charge is effectively delocalized at the nitrogen position. One classic reaction is the Chichibabin reaction (Aleksei Chichibabin, 1914) in which pyridine is reacted with an alkali-metal amide such as sodium amide to form 2-aminopyridine.
In the compound methyl 3-nitropyridine-4-carboxylate, the meta nitro group is actually displaced by fluorine with caesium fluoride in DMSO at 120°C.
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