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Topic: oxidation with H3PO4  (Read 213 times)

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Offline bands

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oxidation with H3PO4
« 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?

Offline chenbeier

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Re: oxidation with H3PO4
« Reply #1 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

« Last Edit: March 01, 2020, 02:16:53 PM by chenbeier »

Offline Borek

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Re: oxidation with H3PO4
« Reply #2 on: March 01, 2020, 03:48:07 PM »
No oxidation here IMHO. Double bond moves, hydrogen moves, but nothing is being oxidized.
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Offline kamiyu2550

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Re: oxidation with H3PO4
« Reply #3 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.

Offline chenbeier

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Re: oxidation with H3PO4
« Reply #4 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.

Offline Borek

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Re: oxidation with H3PO4
« Reply #5 on: March 01, 2020, 05:16:52 PM »
Let me put it differently: nothing gets oxidized by H3PO4 (as the thread subject suggests).
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