2 Preparation of aliphatic amines

Nucleophilic properties Primary amines can be formed by the nucleophilic substitution reaction between haloalkanes and ammonia. CH3CH2Br + 2NH3
CH3CH2NH2 + NH4Br Reaction with ammonia forming primary amine Excess Ammonia dissolved in ethanol is the reagent 3CH C H H Br 3HN: H3C C H H NH3 + Br – In the first step of the mechanism the nucleophile attacks the haloalkane to form an intermediate H3C C H H NH2 + H :NH3 In the second step of the mechanism a second ammonia removes a proton from the intermediate (acts as base) to form the amine H3C C H H NH2 + NH4Br N Goalby chemrevise.org Using an excess of Ammonia can limit further substitution reactions and will maximise the amount of primary amine formed The same reaction mechanism occurs with the secondary amine reacting to form a tertiary amine Reacting primary amines with haloalkanes forming secondary amine Amines will react with haloalkanes in the same nucleophilic substitution reactions that ammonia does above 3CH C H H 2CH Br 3CH2NH2 H3C CH2 NH CH2 CH3 Diethylamine H3C C H H H3C CH2 NH CH2 CH3 Br H3C CH2 N CH2 CH3 CH2 CH3 triethylamine + + CH3CH2NH3 +BrA primary amine will react with a haloalkane to form a secondary amine Reacting secondary amines with haloalkanes to form a teritary amine + H3C CH2 NH2 + CH2 CH3