Excess Ammonia in nucleophilic substitution reactions
Why is excess ammonia required in nucleophilic substitution reactions for example with bromopentane to produce propylamine, why specifically excess?
So you dont get further reactions to form secondary and tertiary amines and quarternary ammonium salts, done to maximise yield
(edited 6 years ago)
Original post by Jennifer50
Why is excess ammonia required in nucleophilic substitution reactions for example with bromopentane to produce propylamine, why specifically excess?
It must be in excess to ensure no further substitutions with ammonia occur.
If instead the halogenoalkane was in excess, then further substitutions will occur until a quaternary ammonium salt is produced.
(edited 6 years ago)
Original post by markschemes
It must be in excess to ensure no further substitutions with ammonia occur.
How do you mean, could you please give me an example?
Original post by Jennifer50
How do you mean, could you please give me an example?
Take for example the reaction of excess bromopropane with limited ammonia.
The usual nucleophilic substitution reaction will occur, forming propylamine.
This propylamine will again react with the bromopropane in another nucleophilic substitution reaction, forming dipropylamine.
This reaction continues until a quaternary ammonium salt is formed, and no further substitution can take place.
The 'R' is any alkyl group (in this example it would be propyl). I'm not sure if you're doing AS chemistry or what your exam board is so check your specification to confirm if you need to know this (just yet).
(edited 6 years ago)
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