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I'm doing an oxidation of an alcohol with Dess–Martin periodinane which works really well but having trouble with the work up. Doing this reaction with about 5 g of alcohol so the reaction ends up using about 17 g of DMP. As the reaction progresses the DMP byproduct crashes out. And working up turns it into a gun that is quite difficult to remove

Running reaction in DCM and work up with bicarb. Even after filtration DMP is still present. Separates fine on a column but with how much there is it seems to be trappings some of my product. I've read that a thiosulphate wash is also used in these reactions, but I don't think this will be useful to get rid of the gum.

Any suggestions?

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It looks like you are not the first to get gummed up by the mono-acetoxy iodinane byproduct of this reaction. A seemingly simple solution is given in this article about converting an alcohol to ketone via DMP:

The mono-acetoxy iodinane by-pdt can be converted to easier to remove by-pdts during workup by treatment with aq $\ce{NaOH}$ or $\ce{Na2S2O3}$.

This is not a procedure I have experience with specifically, so I hope this a do-able solution for your problem as I understand it. Good luck regardless.

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The answer to your question really depends on your aldehyde, and how sensitive it is (for instance if it's chiral at the alpha position then you don't want to be doing aqueous work ups with anything basic).

1. Filtration

Filtration is by far the most convenient work up for a DMP as the filtrate is often clean enough to telescope through into another reaction.

Firstly, if your reaction isn't already buffered with sodium bicarbonate, add a spatula tip before trying to filter, it quenches out any acetic acid which will not be trapped by the column.

Secondly, add something like ether or hexanes— the DMP related stuff isn't soluble in these, so they'll just sit as solids on the top of your column compared to if you elute with a tonne of dichloromethane for example.

As you've found, it can be a little difficult as the amount of solid gets quite large and traps product. Using a sintered funnel under vacuum makes it far easier, as does using a wide but thin plug rather than a long column.

2. Aqueous workup

I often avoid this one because if I'm doing a DMP it usually means I'm making a very sensitive aldehyde and don't wish to have it sitting around removing the last traces of water afterward.

As AirHuff notes, aqueous thiosulfate washes are very effective. As previously, I'd suggest initially quenching with sodium bicarbonate (a solution this time), then extracting with ether, followed by a final thiosulfate wash, drying, and evaporation.

3. Avoid DMP entirely

As a reagent DMP is great for doing small scale reactions as you essentially add a scoop of reagent and solvent in an open flask and it's done in ten minutes.

On a large scale however the procedure generates a lot of solid byproducts, which can, as you've discovered be difficult to remove. There is also a huge cost associated with DMP, even when prepared in house. For the material you have, you'd be better served doing a different oxidation.

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  • $\begingroup$ Thanks! I tried again today. Thiosulphate wash definitely made it more crystalline and easier to filter than the previous gum. $\endgroup$ – loltim Mar 27 '17 at 0:22
  • $\begingroup$ After a few more repeats of this turns out the base washes are essential. If your compound is base-stable then washing with higher molarity base works much better, e.g. 4M KOH $\endgroup$ – loltim Aug 25 '17 at 1:30
  • $\begingroup$ A base wash would indeed help. Though if your aldehyde is stable to strong base, I would question why you're bothering with DMP at all ... $\endgroup$ – NotEvans. Aug 25 '17 at 8:45

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