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Topic: How does nitric acid convert benzoin to benzil?  (Read 30077 times)

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Offline janapix

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How does nitric acid convert benzoin to benzil?
« on: May 23, 2012, 08:51:28 AM »
I'm working on the mechanism of a multi-step synthesis and am having trouble with how this proceeds:

image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/q1.png

Where/how does initial attack occur?
NO2 gas is lost so I assume this proceeds through a nitrate ester.

Could someone please help me with this?

Offline discodermolide

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Re: How does nitric acid convert benzoin to benzil?
« Reply #1 on: May 23, 2012, 11:58:19 PM »
I'm working on the mechanism of a multi-step synthesis and am having trouble with how this proceeds:

image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/q1.png

Where/how does initial attack occur?
NO2 gas is lost so I assume this proceeds through a nitrate ester.

Could someone please help me with this?


Presumably you get the nitrite ester as you said, R2HC-ONO2 this will eliminate NO2 by abstraction of the proton of the nitrite ester with formation of the ketone.
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Offline Schrödinger

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Re: How does nitric acid convert benzoin to benzil?
« Reply #2 on: May 24, 2012, 04:39:15 AM »
^Pretty much the same mechanism as chromic acid. Chromate ester is formed, and the Chromate part is eliminated by the abstraction of a proton.
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Offline janapix

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Re: How does nitric acid convert benzoin to benzil?
« Reply #3 on: May 24, 2012, 08:32:45 AM »
Thank you both. I believe I've got it now:

image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2.png

Offline discodermolide

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Re: How does nitric acid convert benzoin to benzil?
« Reply #4 on: May 24, 2012, 09:27:49 AM »
Thank you both. I believe I've got it now:

image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2.png

Not quite the last step is removal of the proton next to the nitrate ester with elimination of NO2 and formation of the ketone.
A N-O bond containing a positive N atom cannot loose a further two electrons.
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Offline orgopete

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Re: How does nitric acid convert benzoin to benzil?
« Reply #5 on: May 24, 2012, 04:15:05 PM »
Thank you both. I believe I've got it now:

image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2.png

You have five bonds to the carbon. The CH is still present from the curved arrows.
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Offline janapix

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Re: How does nitric acid convert benzoin to benzil?
« Reply #6 on: May 24, 2012, 09:31:27 PM »
Cheers... that was pretty thick of me to not notice the valency of N or C...
Hopefully THIS one is right =)

image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2-1.png

Offline discodermolide

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Re: How does nitric acid convert benzoin to benzil?
« Reply #7 on: May 25, 2012, 12:26:21 AM »
Cheers... that was pretty thick of me to not notice the valency of N or C...
Hopefully THIS one is right =)

image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2-1.png


This looks better now.
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Offline janapix

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Re: How does nitric acid convert benzoin to benzil?
« Reply #8 on: May 26, 2012, 05:11:07 AM »
=D excellent. Thanks.

Offline orgopete

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Re: How does nitric acid convert benzoin to benzil?
« Reply #9 on: May 26, 2012, 04:39:22 PM »
The acetate ion concentration is probably zero in nitric acid. Water is the most likely base present.
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