Mechanism of oxidation of fluorene to fluorenone?

Answer 1

I'm not positive about the correct mechanism, but I can propose one that seems plausible. Oxygen can exist as a singlet or triplet species. The triplet species (O-O with 2 lone pairs and a radical on each O) is the ground state species, so unless O2 is excited, it will most likely react in this manner.

Using that assumption, O2 can abstract a proton radical from flourene to form a fluorene radical (with the radical at the benzylic position). This is the initiation of a radical chain process. Next, the peroxy radical can attach to the fluorene radical (thus terminating the chain). Alternatively, another O2 molecule can attach to the fluorene radical. This peroxy fluroene radical can abstract a proton from a fluorene molecule, propogating a fluorene radical. In either case, the resulting species is a peroxy fluorene molecule. Now, you can draw a mechanism where a hydroxide anion (the reaction is run in base) pulls off the remaining benzylic proton, pushing electrons into a carbon to oxygen pi bond, and breaking the oxygen-oxygen single bond to release hydroxide.

As I said, I have no evidence for this mechanism, just using my chemical knowledge and experience.