[Kogelbauer]

Hi all

I have this question about the oxidation of 3-carene to 3-carene-5-one using Cr/pyridine as a catalyst. The question asks why a ratio of 2:1 pyridine to CrCl3 is best and then to draw two possible catalytic intermediates that may participate in the reaction

Thanks for any help

[Babcock_Hall]

According to forum rules, you must show your attempt first, before we can help you.

[Kogelbauer]

Well a ratio of 2:1 could mean that each pyridine molecule takes a H off 3-carene, however the N does not have any lone pairs of electrons to do this with.

One of the three Cl-'s could take a H off a carbon of 3-carene, but that does not suggest why a ratio of 2:1 is most effective

[discodermolide]

Pyridine most certainly forms a complex with CrCl₃, probably CrCl₃Py_x. I'm not sure how many Py's are in the complex probably 3.
This most certainly modifies the behaviour of the reagent in this oxidation, making it more selective or preventing over oxidation.
It's akin to using modified borohydrides or aluminium hydrides to make the reduction more selective and prevent over reduction.