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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: bands on March 01, 2020, 01:50:00 PM

Title: oxidation with H3PO4
Post by: bands on March 01, 2020, 01:50:00 PM
Hi there, I can only find literature detailing use of H3PO4 to dehydrate an alcohol, but the question shows it being oxidised to a ketone. Can anyone help with this mechanism?
Title: Re: oxidation with H3PO4
Post by: chenbeier on March 01, 2020, 01:59:34 PM
Addition of H+ at C 5 at the double Bond. Markovnikov product. Then Hydrid Transfer from the C2  to the C 6. Then elimination H+  from the oxygen.

The same could also happen between two molecules

Title: Re: oxidation with H3PO4
Post by: Borek on March 01, 2020, 03:48:07 PM
No oxidation here IMHO. Double bond moves, hydrogen moves, but nothing is being oxidized.
Title: Re: oxidation with H3PO4
Post by: blackcat on March 01, 2020, 04:17:30 PM
Agree with Borek that there is no net oxidation. Indeed, the alkene is hydrogenated (reduced) while the alcohol is oxidized. Hence this should be a disproportionation. Due to oxophilicity of phosphorus, H3PO4 is unlikely to be an oxidizing agent to donate oxygen.
Title: Re: oxidation with H3PO4
Post by: chenbeier on March 01, 2020, 04:48:05 PM
No oxidation here IMHO. Double bond moves, hydrogen moves, but nothing is being oxidized.

I  would not say in this way. Conversion alcohol to get a keton is an oxidation. In this special molecule at same time the double bond will be reduced.

So there will be an oxidation and also an reduction, an internal redox reaction.
Title: Re: oxidation with H3PO4
Post by: Borek on March 01, 2020, 05:16:52 PM
Let me put it differently: nothing gets oxidized by H3PO4 (as the thread subject suggests).