June 12, 2021, 10:39:13 AM
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Topic: Alkylation of Amines via an "ether synthesis" why doesn't it stop!  (Read 255 times)

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Offline Monoamine

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So it is well known that you can alkylate amines with Bromoalkanes. My textbook says that this is generally not a good approach though, since this will create a quaternary ammonium cation.
Now, I'm having trouble understanding why this should be, since the liberated Br- ion should form a salt with the amine and so all the lone pairs in the amine should be used up and shouldn't be available for further bonding. (See attached picture).

Incidentally, if you do end up with a quaternion ammonium cation, how can you get rid of one of the extra alkyl constitutes, and is there a way of selecting which one you want to remove?

Any insight is greatly appreciated!  :D

Offline mjc123

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Re: Alkylation of Amines via an "ether synthesis" why doesn't it stop!
« Reply #1 on: March 15, 2021, 06:58:35 AM »
RR2NH is neutral, not a cation.
Initial attack gives RR2NH2+Br-, from which HBr is eliminated. When you get to the quaternary ammonium, you can't eliminate HBr.

Offline Monoamine

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Re: Alkylation of Amines via an "ether synthesis" why doesn't it stop!
« Reply #2 on: March 15, 2021, 07:54:32 PM »
Thanks for he clarification.

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