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    Why does excess ammonia ensure that a primary amine is the major product?

    Would an excess not mean that further substitutions can occur, producing secondary and tertiary amines?

    My question is producing an aromatic amine and you need to state that excess ammonia is needed to ensure the primary amine is the major product.

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    (Original post by jazz_xox_)
    Would an excess not mean that further substitutions can occur, producing secondary and tertiary amines?
    Simplify the situation to only one molecule of ammonia in the presence of loads of CH3Cl (or whatever you're reacting it with). The reaction occurs as the N atom in NH3 has a lone pair so can do nucleophilic sub forming CH3NH2. After the amine is formed, the N atom still has a lone pair so can do nuc. sub again, forming (CH3)2NH, which still has a lone pair.

    NOW, reverse the situation, only 1 CH3Cl molecule and loads of NH3. Once the CH3Cl has reacted, the CH3NH2 formed cannot do nuc. sub as it has no CH3Cl to react with.

    Now have loads of NH3 and a bit of CH3Cl. CH3NH2 will form. BUT consider what it is like to be a CH3Cl molecule right now: there is a bit of CH3NH2 formed and loads of unreacted NH3. What are you going to collide with and therefore react with? Most likely NH3. The CH3NH2 is essentially outnumbered and won't get a look-in.
 
 
 
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