Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Zainb on January 31, 2012, 12:55:10 PM

Title: Potassium permanganate and active Manganese dioxide as oxidants
Post by: Zainb on January 31, 2012, 12:55:10 PM

The combination of potassium permanganate and active manganese dioxide (KMnO₄/MnO₂) produces a reagent that can be used effectively for the oxidation of alcohols to carbonyl compounds as shown below.

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.organic-chemistry.org%2Fabstracts%2Fliterature%2F814c.gif&hash=d54aa67c739c68f5d2cdb1c4626b2afe95fa561b)



Any idea about the resulting reagent from this combination?

Usually KMnO₄ is used to oxidize alkenes.

Thanks for any help..

Title: Re: Potassium permanganate and active Manganese dioxide as oxidants
Post by: discodermolide on January 31, 2012, 03:07:02 PM

Quote from: Zainb on January 31, 2012, 12:55:10 PM

The combination of potassium permanganate and active manganese dioxide (KMnO₄/MnO₂) produces a reagent that can be used effectively for the oxidation of alcohols to carbonyl compounds as shown below.

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.organic-chemistry.org%2Fabstracts%2Fliterature%2F814c.gif&hash=d54aa67c739c68f5d2cdb1c4626b2afe95fa561b)



Any idea about the resulting reagent from this combination?

Usually KMnO₄ is used to oxidize alkenes.

Thanks for any help..

I see you obtained this from the following paper. The title says it all!
I guess it is not a reagent but a supporting medium, similar to Pd/C.

Title: Re: Potassium permanganate and active Manganese dioxide as oxidants
Post by: Zainb on February 02, 2012, 04:31:03 AM

I have seen the complete paper,,, but they did not explain the mechanism...

They used 17.3 equivalents from MnO₂ and just 32 equivalents from KMnO₄,,, Then the permanganate just a catalyst,,, I try to use this regent on alkenyl compound but the reaction mechanism still unclear.

Title: Re: Potassium permanganate and active Manganese dioxide as oxidants
Post by: orgopete on February 02, 2012, 08:34:28 AM

I have not seen the paper. I don't know that the mechanism for KMnO4 oxidations of benzylic CH's has been proven, but it is generally believed to involve a radical reaction. From there, oxidation reactions generally involve
       H-C-O-X  :rarrow: H⁺ + C=O + X^-

where X is any group able to accept electrons, MnO_n, CrO_n, Br, Cl, Ag, etc.

Although the first step is usually carried out a elevated temperatures (to improve radical formation?), the reference reaction was carried out under mild conditions. If your substrate fails to react, I should presume the radical allylic oxidation step has a higher activation energy than is being supplied in this reaction. (If you have an alkene, I am surprised the hydroxylation reaction (similar to OsO₄ oxidation) is not occurring directly.)

Title: Re: Potassium permanganate and active Manganese dioxide as oxidants
Post by: Zainb on February 15, 2012, 03:15:16 AM

the hydroxy group is a good nucleophile, which will attack the metal atom centr in the MnO₂ (SN²) and  then one of oxynium atom of the intermediate, R₂-CH-O-MnO₂H, will depronate the proton in the cyclic transition state leading to the carbony compound