Preparation and Reactions of Amines



There are a variety of reactions available for the synthesis of primary amines, but there are only two reactions that reliably generate secondary and tertiary amines: reductive amination of aldehydes and ketones and the reduction of amides. Many reactions used to synthesize amines involve one amine being used to synthesize another amine. The Hofmann elimination is used to generate an alkene from a primary amine, and the Sandmeyer reaction is used to convert aromatic amines to a variety of other compounds by way of an aryl diazonium ion intermediate.

At A Glance

  • Amines can be prepared through a variety of methods.
  • Amines can be prepared by the reductive amination of a ketone or aldehyde with an amine (NH3, RNH2, or R2NH2), acid catalyst (H+), and NaBH3CN. Amines can also be prepared through the reduction of their respective amide, nitrobenzenes, nitriles, or oximes.
  • Primary amines can be prepared by adding ammonia to an alkyl halide, using the Gabriel synthesis with an alkyl halide, or using a nucleophilic substitution reaction to produce an alkyl halide and then reducing the azide group.
  • Primary amines can be prepared by the Hofmann rearrangement of primary amides or the Curtius rearrangement of acyl azides.
  • The reactions of amines include acylation, Hofmann elimination, and diazonium reactions.
  • Acylation of amines occurs via the addition of an acid chloride to an amine. The Hofmann elimination occurs when a primary amine is treated with excess methyl iodide (CH3I) followed by silver oxide (Ag2O), water (H2O), pressure, and heat. The product is the least substituted alkene (the Hofmann product).
  • Amines react with nitrous acid to form diazonium salts, N-nitroso amines, or aryl diazonium salts. The aryl diazonium ion formed when aniline is treated with sodium nitrate and hydrochloric acid can be converted to a variety of other groups (Br, Cl, I, CN, OH, H, or F). Aryl diazonium salts can also couple with other aromatic compounds to form azo compounds that are often used as organic dyes.
  • Important nitrogen heterocycles include pyrrole, imidazole, pyridine, pyrimidine, and indole. Two of the significant reactions involving nitrogen heterocycles are both electrophilic aromatic substitution reactions.