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Topic: Mechanism help with NaBH4.  (Read 2509 times)

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Offline elupuu

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Mechanism help with NaBH4.
« on: March 27, 2013, 05:08:05 PM »
So I need to know the mechanism for the reduction of para-nitrophenol with NaBH4 with Pd/C catalyst.

I initally proposed a mechanism in which oxygen offers his lone pair to BH3 and hydride attacks the nitrogen. OBH3- is the leaving group and the reaction happens again for the other oxygen.

Offline Corribus

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Re: Mechanism help with NaBH4.
« Reply #1 on: March 27, 2013, 05:29:29 PM »
Then why do you need the catalyst?
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline elupuu

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Re: Mechanism help with NaBH4.
« Reply #2 on: March 27, 2013, 06:47:16 PM »
That's what problematic, if the catalyst is needed and my route doesnt include it then my mechanism is flawed and I need to see the real mechanism.

Offline discodermolide

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Re: Mechanism help with NaBH4.
« Reply #3 on: March 27, 2013, 08:17:21 PM »
That's what problematic, if the catalyst is needed and my route doesnt include it then my mechanism is flawed and I need to see the real mechanism.


What product do you expect from this reduction?
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Offline weidaibao2008

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Re: Mechanism help with NaBH4.
« Reply #4 on: March 28, 2013, 04:14:14 AM »
That's what problematic, if the catalyst is needed and my route doesnt include it then my mechanism is flawed and I need to see the real mechanism.
The product should be  is 4-Hydroxyaminobenzene

What product do you expect from this reduction?

Offline discodermolide

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Re: Mechanism help with NaBH4.
« Reply #5 on: March 28, 2013, 04:19:45 AM »
What is your reaction solvent?
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Offline elupuu

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Re: Mechanism help with NaBH4.
« Reply #6 on: March 28, 2013, 10:54:04 AM »
The solvent is an aqueous solution of NaOH and the expected product is para-hydroxyaniline.

Offline discodermolide

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Re: Mechanism help with NaBH4.
« Reply #7 on: March 28, 2013, 11:50:03 AM »
OK thanks.
In this case is the aqueous NaOH and NaBH4 not generating hydrogen which is reducing the nitro group using the catalyst?
So effectively you are doing a hydrogenation with an internal  hydrogen source instead of using a hydrogen cylinder.
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Offline elupuu

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Re: Mechanism help with NaBH4.
« Reply #8 on: March 28, 2013, 04:42:19 PM »
I dont believe generating hydrogen is possible with the conditions Im having. Also I found out NaBH4 is required in 4 equivalents.

Offline orgopete

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Re: Mechanism help with NaBH4.
« Reply #9 on: March 28, 2013, 04:55:49 PM »
So I need to know the mechanism for the reduction of para-nitrophenol with NaBH4 with Pd/C catalyst.

I initally proposed a mechanism in which oxygen offers his lone pair to BH3 and hydride attacks the nitrogen. OBH3- is the leaving group and the reaction happens again for the other oxygen.

This mechanism does not seem to need Pd/C. I too thought BH4(-) was a hydrogen source. I didn't think borohydride reduced nitro compounds, but especially an acintro anion. Although I did not anticipate palladium accepting electrons from borohydride, that is the same net result as the addition of H2 to palladium. If need be, I'd write the addition of hydride to palladium followed by protonation of the anion. Use this reductant to convert a nitro group to an amine (over several steps).
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