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SolutionsAzides

1. Products

  1. Benzyl bromide + NaN3; then LiAlH4
  2. Propylene oxide + NaN3; then H2/Pd
  3. Benzoyl chloride + NaN3; heat
  1. Benzyl azide and, after reduction, benzylamine.
  2. 1-Azido-2-propanol (attack at the less hindered carbon) and, after reduction, 1-amino-2-propanol.
  3. Benzoyl azide, which on heating loses N2 and rearranges to phenyl isocyanate (Curtius rearrangement).

2. Advantages of azide

What advantages does the NaN3/LiAlH4 sequence have over the reaction of the halide with ammonia for preparing primary amines?

The organic azide is not nucleophilic, so there is no polyalkylation: only the primary amine is obtained. Moreover, the azide anion is an excellent, weakly basic nucleophile, so the SN2 works well even with secondary substrates.

Caution: low-molecular-weight azides can be explosive.

3. Stereochemistry

Which amine is obtained from (R)-2-bromobutane with NaN3 and then LiAlH4?

(S)-2-Butylamine: the SN2 with azide inverts the configuration and the reduction does not affect the stereocentre.

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