Tuesday, July 21, 2009

Oxidation of Secondary Alcohols by Sodium Hydride ?

Xinbo Wang, Bo Zhang and David Zhigang Wang
School of Chemical Biology and Biotechnology, Shenzhen Graduate School of Peking University, Shenzhen, China 518055
J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja904224y
Publication Date (Web): July 21, 2009

In this recent paper, a novel oxidation of Secondary Alcohols by Sodium Hydride was described.

. they said "Uncovered here are some unprecedented reactivities of this classical reagent under very mild conditions, including alcohol oxidation, tandem allylic alcohol oxidation−hydride conjugate reduction, and aldehyde oxidative amidation. These readily implementable transition-metal-free processes feature exceptional material accessibility, operational simplicity, and environmental compatibility."

very nice work.
while reading this paper, some thoughts popped out of my little brain.
Could it be some other metal species instead of NaH really catalized the rxn?

it is known that nah is a base, sometimes can be a hydride donor, but Na+ never seen as a hydride acceptor.
I guess there is something else which catalized the rxn.
1. although nah is catalyst and all recoved after rxn, they still need a huge amount.
2. nah is made from na metal, presence of trans metal such as Pd is very possible.
3. there is an example by a japanese group which found a heck coupling rxn without pd, but finally they said the base they used (t-buOK, K2CO3?) contains trace of pd which did the trick.
(can't really remember all the detail, sorry).

anyway, this is still a very useful rxn and I hope to see more detailed research on this topic which may answer my question.

They already found O2 is essential for the rxn to happen.


Anonymous said...

Just found your nice blog and have to give you encouragement - keep up the good work!
This paper just doesn't sound right. There is something very weird to catalytic oxidation of benzylic alcohols by sodium hydride. I'd follow your bet on the impurity profile of NaH.

mollux67 said...

When they screen the solvent for the reaction, you can see that it only works with THF. The fact is that THF is a solvent that dissolves molecular oxygen very easily, and they may have used non-distilled/dry THF.
So when they're using the NaH, they are deprotonating the alcohol into alcoholate, which reacts very easily ith dioxygen in order to be oxydised into cetone.
By the way, even the mechanistic proposal they made is totally stupid. With this mechanism, we wood have as overall scheme :
R2-OH + NaH => R2=O + NaH + H2
NaH would be catalytic, no need of 2equivalents of NaH...

I can't believe that a director of a laboratory to put this up in a JACS, and that at least an associate editor and two referees read that paper...

So sad for science...

Weiwei TIAN said...

Thank you for your comment.
I agree with you totally. Fortunately, this kind of paper is rarely seen in jacs.

Anonymous said...

Genial post and this enter helped me alot in my college assignement. Thank you for your information.

Anonymous said...

Well I to but I about the post should acquire more info then it has.

Anonymous said...

tvv2008.blogspot.com; You saved my day again.

Anonymous said...

Hello friends
Do not miss your chance to get a free ipad. Visit http://bit.ly/d9QOON