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Author: Subject: CrO3 Oxidation Mechanism on Carbon
Blind Angel
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[*] posted on 24-3-2010 at 11:03
CrO3 Oxidation Mechanism on Carbon


Does anybody have laying around or in their head the mechanism of the oxidation of alpha-carbon on aryl compound (i.e. 1-Phenylethane) using CrO3 or Cr2O7 in acidic condition, I'm guessin it involve radical but I have a hard time seeing it and all then info I'm finding is about oxidation of alcohol.



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Sandmeyer
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[*] posted on 3-4-2010 at 07:55


Correct, this is a radical process - the hydrogen abstraction (by the oxygen of chromic acid) will initially take place at the carbon giving the most stable radical (i.e benzylic -CH2-), hence:

PhCH2CH3 + Cr6+ ---> [PhCH(Cr5+)CH3] --[C-O bond formation to give Cr(IV)ester]--> PhCHO(Cr4+)CH3 followed by hydrolysis of ester to alcohol, PhCHO(Cr4+)CH3 + H2O --[hydrolysis]--> PhCH(OH)CH3 + Cr4+ further oxidation of alcohol to ketone gives acetophenone.


[Edited on 3-4-2010 by Sandmeyer]




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Sandmeyer
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[*] posted on 3-4-2010 at 10:03


For a more detailed discussion on mechanism see the following article by Wiberg and Foster (attached) - highly recomended.

Kenneth B. Wiberg, Gordon Foster
J. Am. Chem. Soc., 1961, 83 (2), pp 423–429
DOI: 10.1021/ja01463a041


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kmno4
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[*] posted on 13-5-2010 at 01:48


I have just found this article :
"On the mechanism of the oxidation of hydrocarbons with chromic acid and chromyl chloride"
http://linkinghub.elsevier.com/retrieve/pii/S004040200198982...
It should be helpful.

[Edited on 13-5-2010 by kmno4]
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