ZHANGNIUBI
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Need help! who knows the mechanism of Kharasch-Brown Reaction
http://edu.emuch.net/attachment/de/b6/1574191_1333982219_395...
here is the reaction.. please tell me why the group -COCl sit on those specific positions on Cube..
and how it works(mechanism)
thank you!
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Nicodem
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It was not easy to find, but this is apparently the seminal paper for this reaction:
Carboxylation. I. The Photochemical and Peroxide-catalyzed Reactions of Oxalyl Chloride with Paraffin Hydrocarbons.
M. S. Kharasch, Herbert C. Brown
J. Am. Chem. Soc., 1942, 64, 329–333. DOI: 10.1021/ja01254a032
See also their preliminary publication on this reaction (DOI: 10.1021/ja01859a515). (For that depicted reaction on cubane, see DOI:
10.1002/anie.199306121)
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ZHANGNIUBI
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Quote: Originally posted by Nicodem  | It was not easy to find, but this is apparently the seminal paper for this reaction:
Carboxylation. I. The Photochemical and Peroxide-catalyzed Reactions of Oxalyl Chloride with Paraffin Hydrocarbons.
M. S. Kharasch, Herbert C. Brown
J. Am. Chem. Soc., 1942, 64, 329–333. DOI: 10.1021/ja01254a032
See also their preliminary publication on this reaction (DOI: 10.1021/ja01859a515). (For that depicted reaction on cubane, see DOI:
10.1002/anie.199306121) |
yes, I know it's hard. But based on my current situation, I can not download these papers by my school's library.
Could you please help download them and put them on here? I ll be very appreciated!!
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francis
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This is a radical chain mechanism. The paper says it can be photochemical but works better with a peroxide initiator.
The cubane is the substrate and the rxn proceeds by benzoyl peroxide decomposition:
(I will call the benzoyl group Bz and include the oxygen-oxygen sigma bond).
Bz-O-O-Bz ---> 2 BzO*
Then the BzO* reacts with oxalyl chloride to form the 'carrier' (the terminal C-Cl bond of the oxalyl chloride is broken):
BzO* Cl-COCO-Cl-> BzO-Cl + *COCO-Cl
Then *COCl decomposes to carbon monoxide (CO) and Cl* radical
*COCOCl -> 2CO + Cl*
The chloride reacts with the cubane to form an alkyl radical by, apparently, breaking of the R-H bond.
R-H + Cl* -> R* + HCl
Apparently the R* reacts with the original oxalyl chloride:
R* + (COCl)2 -> R-COCl + *COCl
The rxn continues when *COCl radical decomposes to CO and Cl* and the Cl* radical reacts with the cubane again as follows:
Cl* + RH -> HCl + R*
Until termination.
Unfortunately the original picture in your post is not up anymore. Maybe you can repost it?
I have attached the paper, see page 3 for the mechanisms (there are no curly arrows but you can imagine they would be single-headed arrows).
Attachment: Kharasch Brown Rxn.pdf (595kB)
This file has been downloaded 769 times
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