Talk:Baeyer-Villiger oxidation

Article Grading: The following comments were left by the quality and importance raters: (edit · refresh)

As I find I am starting the discussion on this topic, I find this a little awkward. I am not one of the authors, a reviewer, nor do I have access beyond the first page that is available from the citation link. Therefore, I only wish to contribute to a discussion, not the article itself.

I am writing a book on reaction mechanisms. Finding and verifying any mechanism can be tenuous at best. However, I began to realize several simple rules. Never use an intramolecular 1,4-proton transfer in protic media unless there is compelling evidence for this to be true. 1,5 okay, 1,6 common. I am still looking for my first violation of a 1,4 transfer. My rational follows closely with Baldwin's rules. Clearly, cyclic mechanisms avoid placing a high entropic constraint on a reaction. So, am I the only person who is skeptical that the Baeyer-Villiger mechanism would actually involve three peroxyacid molecules lined up with three linear O-H-O bonds in a concerted reaction?

I am sympathetic with Yamabe and how to deal with proton transfers. I also agree with 180° being the best angle, but beta-keto acids decarboxylate readily without being 180° angles. (I don't know whether that cyclic mechanism has been verified however.) In my book, I have tried to soft pedal the problem of how additions to carbonyl groups actually occur. Under basic conditions, attack of an anion is plausible and under acidic conditions, attack of a neutral nucleophile to a protonated carbonyl groups is also plausible. However, how does an alcohol or water add to an aldehyde? Is it a concerted reaction reaction with two moles of water or alcohol? This would be one of my instances of a 6-membered proton transfer through two moles of solvent. The alternate is just add it and get a neighboring oxonium ion and an alkoxide. I eschewed using two additional moles of solvent to create a concerted proton transfer to avoid creating the indicated charge imbalances. In a protic medium, the solvent can effect the necessary proton transfers. I can't answer that question, but isoelectronic charged intermediates seem very reasonable in enamine and imine formation.

In lieu of no further information, I don't have the full paper to read, I didn't review the paper to make my doubts directly to the authors, so I don't have anything to require a change in the proposed mechanism. However, I am doubtful of its accuracy.

One additional bias I confess to, I take a rather liberal view of concerted. To paraphrase what Knowles might have said, "If time can be divided into infinitely small portions, then three billiard balls cannot collide at the same time." If that were true, then no reactions can be truly concerted. I find this bias in greater agreement in explaining reactions than to assert that electron transfers are concerted. Concerted reactions should avoid charge imbalance, yet it is difficult to find reactions in which reactivity is unaltered by electron availability. Even ozonization reactions, which I do write as a concerted electrocyclic reaction, are easier to explain if electron availability is a factor. Petedskier (talk) 01:15, 3 February 2008 (UTC)