I'm currently in the third quarter of organic chemistry. So far, we've learned that Na2Cr2O7 will react with secondary alcohols to form ketones, and likely form carboxylic acids from primary alcohols, though my book and lecture did not confirm this.
More recently, we learned it will also a benzylic carbon so long as it is not quatenary. (other conditions: H3O, Heat). I'm curious about how it can do this.
Ar=Benzene. Start: Ar-CH-(CH3)2, End: Ar-COOH. If you react Ar-CH-(CH3)2 with Na2Cr2O7, H3O, Heat, you get Ar-COOH (and likely CH3-CH3, though that's never been specified). I expect it to go something like this. Ar-CH-(CH3)2 -(1)-> [Ar-C(+)-(CH3)2 <--> Ar(+)=C-(CH3)2] -(2)->Ar-C(OH)(CH3)2 -(3)-> Ar-C(=O)CH3 + CH3 -(4)->Ar-COO- + H3O + CH3-CH3 -(5)-> Ar-COOH + H2O. This is the best sort of mechanism I can come up with, though it has many things I'm uncertain about. How does it break carbon-carbon bonds? From what I've learned, C-C bonds tend to be more stable than C-O, C=O, and C-H bonds. I'm certain there must be some kind of resonance with the benzene to make this work, but am unsure as to what it does exactly. I am unsure about how Na2Cr2O7 actually reacts either. I know the structure is something like 2Na+ [O3CrOCrO3](2-) but do not know what this becomes after losing an oxygen, or two.
I'm also curious about KMnO4 - I understand it can take Ar-CH3 to Ar-COOH, but can it do all the same things as Cr2O7? my book/lecture were never clear on this. In addition to that, will other agents such as PCC do anything with a benzylic carbon/OH (Ar-CH2-OH)?
Thank you for any assistance in understanding these.