How Does KMnO4 Oxidize Toluene to Benzoic Acid?

[cuti_pie75]

Hi,

It's been quite some time now I've spent on figuring out the mecanism of the oxydation of toluene with KMnO4 to give benzoic acid. My problem is i don't know how exactly the MnO4 attacks the hydrogen on the aliphatic chain. So, if anyone can help me figure out the first steps of which O on MnO4 will attack, that'll be great!

 

[chem_tr]

Hello

In this process, either radicalic or cationic species form, as seen in a closely related reaction:

$$Ar_2CH_2+CrO_3\longrightarrow Ar_2C=O$$
$$rate~determining~step:Ar_2CH_2 \longrightarrow Ar_2CH \cdot ~or~Ar_2CH_2 \longrightarrow Ar_2CH^+$$

I'm certain about a benzyl cation or benzyl radical will be produced in this reaction you're asking about.

 

[movies]

I think chem_tr is right. The first step is a hydrogen atom abstraction (that is, a proton plus an electron) to give a benzyl radical. That can then combine with a water molecule (water is typically the solvent for these oxidations) to give benzyl alcohol. The oxidation from the alcohol to the acid is much more straight forward and probably doesn't involve radicals.