Excess of Ammonia

[osmosis786]

Bromoethane is reacts with ammonia via a nucleophilic substitution to produce ethylamine.

What I want to know is why is ammonia needed in excess to produce a high yeild of ethylamine?

[TheMasterMind]

Bromoethane is reacts with ammonia via a nucleophilic substitution to produce ethylamine.

What I want to know is why is ammonia needed in excess to produce a high yeild of ethylamine?

If excess ammonia, it is possible to get two reactions, one of

CH3CH2Br + NH3 ----> CH3CH2NH3 + Br-

CH3CH2NH3 + Br- + NH3 ----> CH3CH2NH2 + NH4 + Br

The second ammonia molecule takes the hydrogen ion from ethylammonia bromide, giving you ethyl amide and ammonia bromide. overall your reaction is :

CH3CH2Br + 2NH3 ----> CH3CH2NH2 + NH4+Br-

Note: ethyl amine is a strong base and will never give it's hydrogen ion off to a weaker base such as ammonia. Note: this will only occur if there is an extreme amount of ammonia.

did you that it more clear?

[osmosis786]

So, what you're saying is that because there are two reactions able to occur, excess is needed to produce the latter reaction, rather than the former just occuring?

Thanks.

[TheMasterMind]

So, what you're saying is that because there are two reactions able to occur, excess is needed to produce the latter reaction, rather than the former just occuring?

Thanks.

Essentially what I am saying is that with an excess of ammonia, both reactions are possible.