Sciencemadness Discussion Board

CrO3 Oxidation Mechanism on Carbon

Blind Angel - 24-3-2010 at 11:03

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.

Sandmeyer - 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]

Sandmeyer - 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

Attachment: ja01463a041.pdf (996kB)
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kmno4 - 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"
It should be helpful.

[Edited on 13-5-2010 by kmno4]