[paneri]

How can we purify an oxidation of an alcohol realized with Dess-martin so as not to be seen in the NMR spectrum.
Has anyone a clue?
Thanx

[discodermolide]

How can we purify an oxidation of an alcohol realized with Dess-martin so as not to be seen in the NMR spectrum.
Has anyone a clue?
Thanx

Column chromatography?

[Honclbrif]

So the Dess-Martin byproduct won't be seen on NMR, so the oxidized alcohol won't be seen by NMR, or so that the means of purification won't be seen by NMR?

[Dan]

I use a reducing solution to destroy the DMP:

1. Dilute your reaction mixture with a suitable organic solvent.
2. Stir it vigorously with an equal volume of 8% w/v aqueous sodium thiosulfate solution saturated with sodium bicarbonate for about 30 mins. This should destroy the excess DMP.
3. Discard the aqueous, and wash twice more with the thiosulfate/bicarb solution.
4. Brine wash if you want/need to.
5. Dry organic over MgSO₄ (or equvalent), filter, concentrate and column if required.

[paneri]

Firstly,I have to point out that we have 2 aldehydes and our substance is sensitive to acidic conditions.So we took a crude NMR and saw a lot of DMP in the spectrum.
We ran a quick column but the spectum was not cear with a lot of dess-martin..
The crude NMR was better..
 

[discodermolide]

Firstly,I have to point out that we have 2 aldehydes and our substance is sensitive to acidic conditions.So we took a crude NMR and saw a lot of DMP in the spectrum.
We ran a quick column but the spectum was not cear with a lot of dess-martin..
The crude NMR was better..
 

You should have used TEMPO/bleach in a two phase system with good stirring. More efficient and no side products, the aldehyde can then be used directly.
Dess-Martin is really a crappy reagent and is dangerous to use on scale.

[Dan]

Dess-Martin is really a crappy reagent.

I've never got less than 90% yield for DMP oxidations and the products never required chromatography.

Nothing wrong with TEMPO oxidations though.

We made DMP in-house in my previous lab. Cheap, easy and clean, safe to synthesise on 100 g scale by this method (and references therein for IBX -> DMP):

Frigerio, M.; Santagostino, M.; Sputore, S. J. Org. Chem. 1999, 64, 4537

[discodermolide]

Dess-Martin is really a crappy reagent.

I've never got less than 90% yield for DMP oxidations and the products never required chromatography.

Nothing wrong with TEMPO oxidations though.

We made DMP in-house in my previous lab. Cheap, easy and clean, safe to synthesise on 100 g scale by this method (and references therein for IBX -> DMP):

Frigerio, M.; Santagostino, M.; Sputore, S. J. Org. Chem. 1999, 64, 4537

DMP is heat- and shock-sensitive, and shows an exotherm when heated >130 °C. As far as I remember the exotherm is quite large. The risk analysis we employed did not allow it's use.
Run a DSC if you can in your labs.

[Honclbrif]

DMPs always been pretty good to me. It was the only thing that worked to make an aldehyde with skipped conjugation. Never used it on anything other than ice so exotherms have never been a problem, and it came as a solution in DCM, so shock sensitivity wasn't a big issue either. Only complaint I have is that its pricey and degrades fairly rapidly after you open the bottle.

[discodermolide]

DMPs always been pretty good to me. It was the only thing that worked to make an aldehyde with skipped conjugation. Never used it on anything other than ice so exotherms have never been a problem, and it came as a solution in DCM, so shock sensitivity wasn't a big issue either. Only complaint I have is that its pricey and degrades fairly rapidly after you open the bottle.

On scale the DCM solution is too dilute to be of any use. Apart from that DCM is frowned upon in industry, we were not allowed to use it because of emissions in-spite of the cat.ox. The cat.ox. had to have it's temperature increased to ensure complete degradation, which shortened its life. Furthermore we had to inform H&S whenever it was used on scale, and believe me they monitored every last atom.

[Honclbrif]

I'm so used to academic work that its easy to forget there's parts of the world where chemistry is done very, very differently. I can't imagine trying to work without DCM. Its the only thing that works as a solvent for half my reactions.

Out of curiosity, what do you use as a replacement for it?

[discodermolide]

I'm so used to academic work that its easy to forget there's parts of the world where chemistry is done very, very differently. I can't imagine trying to work without DCM. Its the only thing that works as a solvent for half my reactions.

Out of curiosity, what do you use as a replacement for it?

THF or Me-THF or an acetate (if it does not react)