Cloner
Hazard to Others
Posts: 150
Registered: 7-12-2004
Member Is Offline
Mood: apocalyptic
|
|
DMSO separations
Does anyone know a way to get dissolved organics out of DMSO? It is a good solvent for many things but it boils too high for thermally acceptable
distillation and even a very gentle setup with a high vacuum will be difficult at best.
I know no azeotropes of DMSO and neither does the marsden solvent guide. The remaining option would be to find another solvent of low viscosity that
has a strong enthalpy with DMSO, hopefully leading to precipitation of dissolved organics.
|
|
|
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
Dillute DMSO with water
The standard method is to dillute the DMSO solution with water and then extract with a non-polar solvent (CH2Cl2, ether, toluene...). Then you wash
the organic layer with brine at least 3 times, but preferably 5 times or more (unless the compound is too soluble in water). This removes the most of
the DMSO away.
Of course you have to addapt the isolation procedure to fit the properties of your product.
Actually there are some azeotropes with DMSO but I don't remember which ones. I think with toluene... but even if so, I see no advantge in
distilling off the DMSO - you may end up distiling your product away at the same time.
|
|
|
Protium
Harmless
Posts: 27
Registered: 25-12-2004
Location: Point Of Return (Subject To 15% Restocking Fee)
Member Is Offline
Mood: unenlightened
|
|
You might be able to extract the organics with a solvent that is not miscible with DMSO. For this to work, the organic must be more soluble in the
extraction solvent than in th DMSO.
DMSO is immiscible with cyclohexane, diethyl ether, heptane, hexane, iso-octane, pentane, and o-xylene.
One could also add water (unless your compound you wish to extract must be kept free of water for some reason) to the DMSO solution until precipitate
or cloudiness is noticed and then extract with an immiscible solvent.
Keep in mind that some of these solvents may have relatively high boiling points themselves. Depending on your specific circumstances and nature of
the compound(s) at hand, some solvents may perform very differently than others.
Experiment with small volumes/amounts until you find the perfect extraction solvent/technique. It is almost always better to do multiple extractions
with smaller volumes of solvent than to perform one large extraction.
It just depends on how you look at it...
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
Why not simply steam distill the DMSO out? Simply lead steam through your DMSO solution and anything volatile at the temperature of the flask/steam
will be carried off with the water vapor. This can all be condensed and re-used. The only problem would be if the stuff you’re trying to purify is
volatile as well.
|
|
|
Cloner
Hazard to Others
Posts: 150
Registered: 7-12-2004
Member Is Offline
Mood: apocalyptic
|
|
For some reason, the compound does not come out if water is added. That while it is water insoluble even in sonication. I have bloody little of the
compound, though, that might be part of the problem. It is a gift of somebody who wanted me to do an analysis.
Steam distillation I think, it cannot be done with water as it is miscible with DMSO well. But I assume a high boiling liquid which is immiscible with
DMSO would do the trick? I can try this next.
[Edited on 20-1-2005 by Cloner]
|
|
|
Marvin
National Hazard
Posts: 995
Registered: 13-10-2002
Member Is Offline
Mood: No Mood
|
|
While you tell us so little about the compound itself its rather difficult to make suggestions. I'm unsure how well this would work with water
added, but have you thought about freezing the DMSO/compound out? This should at least work to concentrate the compound and alone may effect a
seperation on melting (just before it starts to dissolve). If the compound freezes lower or there is too small an amount to seperate mechanically,
combined with an immiscable solvent extraction freezing the DMSO should push all of the compound into the non freezing layer in just a few
extractions.
I assume the usual acid or base extractions cant work, as this would be rather obvious.
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
| Quote: | Originally posted by Cloner
Steam distillation I think, it cannot be done with water as it is miscible with DMSO well. |
It can be tricky reusing the condensed DMSO, but it will surely be removed from the original solution. Miscibility doesn’t matter in the liquid
phase, as long as the vapor is being led away by something (steam). On this thought, why not just evaporate the stuff to dryness at high temperatures?
It might take some time, but not too long if you only have a small amount.
It sounds like the stuff you have now might be a supersaturated solution. The standard solution for this is to scratch the side of the test
tube/beaker the stuff is in with a stirring rod for a while.
|
|
|
JohnWW
International Hazard
Posts: 2849
Registered: 27-7-2004
Location: New Zealand
Member Is Offline
Mood: No Mood
|
|
If the problem is an excessively high normal boiling point of DMSO, 372ºF = 189ºC (see e.g. http://msds.ehs.cornell.edu/msds/msdsdod/a194/m96878.htm , http://www.bulkmsm.com/research/msm/page12.htm , http://www.chemicalland21.com/arokorhi/industrialchem/solalc... , https://www.e-organicchemicals.com/thio/dimethyl/fuse.cfm?ac... ), and the DMSO is desired to be distilled off from less volatile constituents,
the most obvious solution would be boiling and distilling the mixture under reduced pressure.
When heated above its normal boiling point, DMSO degrades, giving off various decomposition products e.g. CH2O, (CH3)2S, CH3SH, SO2, ; see http://www.renovarinc.com/MSDS/CFSE_DMSOnew.pdf . This, and its flash point of 87ºC, are reasons why distillation of DMSO should be done only
under greatly reduced pressure.
|
|
|
mick
Hazard to Others
Posts: 338
Registered: 3-10-2003
Member Is Offline
Mood: No Mood
|
|
DMSO and DMF are strong organic solvents but easily solvated. Wash the organics with saturate salt solution and it could remove the DMSO .
mick
|
|
|
Cloner
Hazard to Others
Posts: 150
Registered: 7-12-2004
Member Is Offline
Mood: apocalyptic
|
|
I don't care about reuse value as I can order DMSO freely.
Distilling DMSO under reduced pressure is tricky. For a start, it's not going to be a comfortable temperature, even at the pressure my pump can
attain. secondly, doing this will take a considerable color to the glass tube connecting to the pump, indicating loss of product.
The compounds are amides with a thiol functionality, MW ranging from 300 to over 1000. THe amide and thiol function are things that make it
excessively difficult to column them. I lost all of the compound doing this over silica as well as alumina. The amides stick too well, I think.
Fucking around with thiols is in general a bad idea, so I will protect them by making them disulfides. That doesn't improve the solubility one
bit, so perhaps they can be made to drop out.
"DMSO and DMF are strong organic solvents but easily solvated. Wash the organics with saturate salt solution and it could remove the DMSO .
"
Now this is interesting. Both DMF and DMSO have the problem of being hard to get rid of. What do you mean with washing the organics? The compounds I
want aren't going to enter a petroleum ether (or younameit) layer, not even if there's a large excess. So, the problem is not getting rid of
DMSO traces.
|
|
|
mick
Hazard to Others
Posts: 338
Registered: 3-10-2003
Member Is Offline
Mood: No Mood
|
|
I was thinking your stuff might be soluble in ethyl acetate, ether or something like that.
If the thiol function is acidic an ion exchange resin column might work
mick
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
