[bands]

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?

[chenbeier]

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

[Borek]

No oxidation here IMHO. Double bond moves, hydrogen moves, but nothing is being oxidized.

[blackcat]

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.

[chenbeier]

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.

[Borek]

Let me put it differently: nothing gets oxidized by H₃PO₄ (as the thread subject suggests).