4
$\begingroup$

If I have 99.9% Reagent ACS, Lab grade Acetone, is it safe to say that it's free of moisture/Anhydrous?

$\endgroup$
  • $\begingroup$ No, that will have some water. I'd guess that you can buy "dry" acetone but it would be expense. Once you open the container and expose it to air then some air will fill the bottle which has at least a small amount of moisture in it and that moisture will migrate into the acetone. You can lower the water content of 99.9% reagent grade acetone by adding molecular sieves to the bottle. That will help keep the acetone "relatively" dry. $\endgroup$ – MaxW Sep 22 '16 at 18:10
  • 1
    $\begingroup$ An important thing to keep in mind is that "dry" isn't necessarily a single thing. Your downstream application determines how much residual water is acceptable. Some applications require much "dryer" solvents than others. Your acetone may be fine for some applications but not others. - Most solvents pick up water from the air, though, in amounts depending heavily on storage conditions. That's why most people re-dry solvents according to their needs, unless they purchase special solvent grades which are certified low moisture and are packaged and stored to limit reintroduction. $\endgroup$ – R.M. Sep 22 '16 at 18:52
4
$\begingroup$

As correctly pointed out by @MaxW, the technical acetone still contains water. In addition, it is better to quantify "dryness", so by passing a mark you may draw the line of "dry enough" for the application you aim for; especially as Karl Fischer analysis may provide you a reproducible figure of merit about the water content.

Now, if you need dry acetone, stirr the acetone with potassium carbonate or calcium chloride and subsequently distill it off into a dry container. In the instance of acetone, however, I refrain from molecular sieves because they catalyze aldol reactions.

| improve this answer | |
$\endgroup$
  • $\begingroup$ Thanks for pointing the problem with molecular sieves and acetone! I've been out of the lab too long. Forgot about that. $\endgroup$ – MaxW Sep 22 '16 at 19:17
  • 1
    $\begingroup$ @MaxW In the welcoming exchange with each other, we learn by the other; in benefit for both sides. $\endgroup$ – Buttonwood Sep 22 '16 at 19:30
1
$\begingroup$

The acetone you have ($99.9~\%$) may be pretty pure but is certainly not dry (anhydrous). The dry solvents we have in the lab are typically marked as $< 50~\mathrm{ppm}\ \ce{H2O}$, which in percent would be $< 0.00005~\%$. In your acetone, however, there are $0.1~\%$ impurities, likely a large amount of which would be water.

If you buy dry acetone (and note that it is much more expensive than the already expensive $99.9~\%$ stuff), remember that it will come in an argon or nitrogen atmosphere and beneath a septum to prevent moisture coming in. Try and keep a positive pressure of whichever inert gas you have in that bottle so it will actually stay dry. Otherwise you will waste a lot of money.

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.