[wytw]

Hello everyone,

I have some questions about Fenton mechanism. I don't really get how we can oxidize some compounds with iron salts and hydrogen peroxide, I know that we produce hydroxyl radicals which abstract hydrogen from substrate, but then what happen with R. ? Considering the fact that we don't have molecular oxygen in the medium.

If we work at a temperature around 100 degree, is it possible to have O₂ incorporation or the T is too low to allow dioxygen activation ?

In the case of benzylic alcohol, which one is easier to oxidize, the benzylic alcohol or the aldehyde obtained by the oxidation of this alcohol, is it the alcohol because of its mesomeric donation effect which promote electrophilic attack by the oxidant?

Thank you for your help ! 

[phth]

benzyl alcohol is easier to oxidize

[wytw]

Thanks !
Is the reason I gave correct ? Thus, the alcohol is easier to oxidize than toluene which only possess alkyl donor (compare to mesomeric effect of alcohol) ?

Any idea for my other issue ?

[phth]

The electron lone pairs stabilize a radical intermediate.  It's a benzyl proton so its pretty low relatively to the sp² radical.  Therefore, there is enormous selectivity.  The aldehyde hydrogen is also less stable sp².  Toluene has the ring effect so it will also be a weak bond.  to summarize: it's the difference of  sp² versus  sp³ radical in the benzyl position.

[orgopete]

Re: Fenton oxidation

In the case of benzylic alcohol, which one is easier to oxidize, the benzylic alcohol or the aldehyde obtained by the oxidation of this alcohol, is it the alcohol because of its mesomeric donation effect which promote electrophilic attack by the oxidant?

I don't know the answer, but what are the products? If you start with a lot of alcohol, the kinetics should favor a build up of aldehyde. When the concentrations are equal, then the easier or kinetically faster reaction will drive its concentration down. Aldehydes are generally quite easy to oxidize and you may find many patents devoted to methods to prepare them. I'm going to suspect that little aldehyde is found in the product.

Re: mesomeric effect
I'm not sure what is being meant here. What is the mechanism of a Fenton oxidation and how should it apply here? Please elaborate.