Preparing Amines (OCR A Level Chemistry)

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Preparing Aliphatic Amines

Preparing Amines

  • Primary amines can be prepared from different reactions including:
    • The reaction of halogenoalkanes with ammonia
    • The reduction of nitriles

Reaction of halogenoalkanes with ammonia

  • This is a nucleophilic substitution reaction in which the nitrogen lone pair in ammonia acts as a nucleophile and replaces the halogen in the halogenoalkane
  • When a halogenoalkane is reacted with excess, hot ethanolic ammonia under pressure a primary amine is formedReaction of halogenoalkanes with ammonia, downloadable AS & A Level Chemistry revision notes

Formation of primary amine

Reduction of nitriles

  • Nitriles contain a -CN functional group which can be reduced to an -NH2 group
  • The nitrile vapour and hydrogen gas are passed over a nickel catalyst or LiAlH4 in dry ether can be used to form a primary amine

Reduction of Nitriles, downloadable AS & A Level Chemistry revision notes

Nitriles can be reduced with LiAlH4 or H2 and Ni catalyst

Reaction of halogenoalkanes with primary amine

  • This is also a nucleophilic substitution reaction in which the nitrogen in the primary amine acts as a nucleophile and replaces the halogen in the halogenoalkane
  • When a halogenoalkane is reacted with a primary amine in ethanol and heated in a sealed tube, under pressure a secondary amine is formedNitrogen Compounds - Secondary Amine Formation, downloadable AS & A Level Chemistry revision notes

Formation of secondary amine

  • Tertiary amines can also be formed by further reaction of the secondary amine
  • In this example, further substitution would form triethylamine (CH3CH2)N

Preparing Aromatic Amines

  • Phenylamine is an organic compound consisting of a benzene ring and an amine (NH2) functional group
  • Nitrobenzene, C6H5NO2, can be reduced to phenylamine, C6H5NH2, according to the following two-stage reaction:

The two-stage reduction reaction of nitrobenzene to phenylamine, downloadable IB Chemistry revision notes

The two-stage reduction reaction of nitrobenzene to phenylamine

Stage 1 - Reduction of nitrobenzene

    • Nitrobenzene, C6H5NO2, is reacted with tin, Sn, and concentrated hydrochloric acid, HCl
      • Tin and hydrochloric acid act as reducing agents
    • The reaction mixture is heated under reflux in a boiling water bath
    • The phenylammonium ions, C6H5NH3+, are protonated due to the acidic conditions

Stage 2 - Formation of phenylamine

    • The phenylammonium ions, C6H5NH3+, are deprotonated by the addition of excess sodium hydroxide solution, NaOH (aq)

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Sonny

Author: Sonny

Expertise: Chemistry

Sonny graduated from Imperial College London with a first-class degree in Biomedical Engineering. Turning from engineering to education, he has now been a science tutor working in the UK for several years. Sonny enjoys sharing his passion for science and producing engaging educational materials that help students reach their goals.