nimgoldman
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Recovering "abused" DMSO solvent
I once done a reaction in DMSO quenched with water and then let two large beakers with used DMSO/water mixture sit on a bench and forgot about them.
I found that DMSO is sensitive to light so it could be hugely degraded at this point.
Since I would have to process it anyway (at least remove all the water before sending it for disposal), I wonder if it's worth recovering.
The mixture is 75% water by volume so I think about first precipitating DMSO by cooling/freezing the mixture to separate bulk of the water. Then I
would remove most of the water with fractional distillation, dry the solvent with CaSO4 and distill under vacuum.
However, I am not sure whether the decomposition products won't affect the quality of the recovered solvent and more steps are needed.
[Edited on 1-6-2019 by nimgoldman]
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PartVIII
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Warning: DMSO can potentially explode when heated to its boiling point at atmospheric pressure (189C), especially in acidic or basic conditions.
The primary decomposition products of DMSO are likely: formic acid (100.8C), Methanesulfonic acid (167C/10mmHg) and sulfate salts. Methyl
methanesulfonic acid (202C) can also be produced and is highly toxic, but it's probably only formed in concentrated DMSO.
I like most of your strategy, except for the precipitation step. You can try it, but it's probably unnecessary and result in a giant loss of time and
yield. I'd just skip straight to distillation. Distill off the water, then replace the receiving flask and switch on the vacuum. There's no need for
fractional distillation. Most of the formic acid and methyl methanesulfonic acid (azeotrope) will come over with the water. Methanesulfonic acid
should remain in the distilling flask.
Dry the distilled DMSO over CaSO4, then check the pH. If it's not acidic, then you're probably good. If it is acidic, then distill it again at a lower
temperature.
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nimgoldman
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The freeze-precipitation didn't work for me anyway, at least down to approx. -14 °C, so boiling off the water followed by vacuum distillation seems
to be way to go. Thanks.
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