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Topic: TLC reductive amination  (Read 12348 times)

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Offline OC pro

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Re: TLC reductive amination
« Reply #15 on: July 08, 2011, 05:59:26 AM »
Your ketone is a kind-of acetophenone, therefore not very reactive. I have done a similar reaction. Triacetoxyborohydride failed in my case completely.
The alternative is, like Dan mentioned before Dean-Stark.
Dissolve equal amounts of ketone and amine in toluene, Dean-Stark it for several hours (oil bath 150 degrees). The imine will be visible on TLC (ninhydrin). In my case it was a bit more unpolar than the ketone. Since there is an equilibrium, you will not get full consumption of ketone. Evaporate the mixture, redissolve in ethanol, add NaBH4 (2equiv) and stir at room temperature. You will get amine and alcohol of your starting ketone which can also be reisolated (and reoxidized). Best yield in my case was 54%.

Offline sjb

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Re: TLC reductive amination
« Reply #16 on: July 08, 2011, 06:27:25 AM »
Your ketone is a kind-of acetophenone, therefore not very reactive. I have done a similar reaction. Triacetoxyborohydride failed in my case completely.
The alternative is, like Dan mentioned before Dean-Stark.
Dissolve equal amounts of ketone and amine in toluene, Dean-Stark it for several hours (oil bath 150 degrees). The imine will be visible on TLC (ninhydrin). In my case it was a bit more unpolar than the ketone. Since there is an equilibrium, you will not get full consumption of ketone. Evaporate the mixture, redissolve in ethanol, add NaBH4 (2equiv) and stir at room temperature. You will get amine and alcohol of your starting ketone which can also be reisolated (and reoxidized). Best yield in my case was 54%.

Isn't the whole point of the Dean-Stark apparatus to remove the water and so drive the equilbrium (in this case) towards imine?

Offline herrhansen

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Re: TLC reductive amination
« Reply #17 on: July 08, 2011, 09:06:25 AM »
Thanks OC.

Have I have seen your method described, but I am just concerned if the imine is stable enough to survive the evaporation of the toluene and to be isolated.

I know you said close to acetophenone, but acetophenone has its ketone at the alpha carbon to the phenyl ring, in my case I have the ketone beta to the phenyl ring. Are you thinking of the steric hindrance as unreactive?

Thanks again.

Offline ak7rb

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Re: TLC reductive amination
« Reply #18 on: March 06, 2018, 03:05:20 PM »
Hey ,

What's the best stain for secondary aliphatic amines

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