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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: janapix on May 23, 2012, 08:51:28 AM

Title: How does nitric acid convert benzoin to benzil?
Post by: janapix 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:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi317.photobucket.com%2Falbums%2Fmm395%2FMunsterMunster%2Fq1.png&hash=22eecabe1ea79df7d08774939683da82662d5c00)
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?

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: discodermolide on May 23, 2012, 11:58:19 PM

Quote from: janapix 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:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi317.photobucket.com%2Falbums%2Fmm395%2FMunsterMunster%2Fq1.png&hash=22eecabe1ea79df7d08774939683da82662d5c00)
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.

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: Schrödinger 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.

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: janapix on May 24, 2012, 08:32:45 AM

Thank you both. I believe I've got it now:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi317.photobucket.com%2Falbums%2Fmm395%2FMunsterMunster%2FUniversity%2520stuff%2Fq2.png&hash=66b3c4502262463a92c02208f0b3ac416c4c5fe9)
image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2.png

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: discodermolide on May 24, 2012, 09:27:49 AM

Quote from: janapix on May 24, 2012, 08:32:45 AM

Thank you both. I believe I've got it now:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi317.photobucket.com%2Falbums%2Fmm395%2FMunsterMunster%2FUniversity%2520stuff%2Fq2.png&hash=66b3c4502262463a92c02208f0b3ac416c4c5fe9)
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.

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: orgopete on May 24, 2012, 04:15:05 PM

Quote from: janapix on May 24, 2012, 08:32:45 AM

Thank you both. I believe I've got it now:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi317.photobucket.com%2Falbums%2Fmm395%2FMunsterMunster%2FUniversity%2520stuff%2Fq2.png&hash=66b3c4502262463a92c02208f0b3ac416c4c5fe9)
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.

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: janapix 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 =)
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi317.photobucket.com%2Falbums%2Fmm395%2FMunsterMunster%2FUniversity%2520stuff%2Fq2-1.png&hash=407f3f3cec2c51d022bcc5de6340b3e403c974a7)
image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2-1.png

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: discodermolide on May 25, 2012, 12:26:21 AM

Quote from: janapix 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 =)
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi317.photobucket.com%2Falbums%2Fmm395%2FMunsterMunster%2FUniversity%2520stuff%2Fq2-1.png&hash=407f3f3cec2c51d022bcc5de6340b3e403c974a7)
image link: http://i317.photobucket.com/albums/mm395/MunsterMunster/University%20stuff/q2-1.png

This looks better now.

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: janapix on May 26, 2012, 05:11:07 AM

=D excellent. Thanks.

Title: Re: How does nitric acid convert benzoin to benzil?
Post by: orgopete 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.