2
$\begingroup$

If I'm washing a methanol solution with chloroform, can I just add water in a 1:1 mixture with the methanol and expect it to break? Do I need to do anything else to cause the aqueous phase to separate (centrifugation, etc..)? Alternatively, are there any better methods, like salting-out the chloroform?


Late edit:

My intention:

I'm just using the chloroform to get rid of other compounds, so once I separate it out, I expect my molecule to be in the aqueous phase, and then to vacuum distill it out.

$\endgroup$
3
  • 1
    $\begingroup$ This likely was a misstep. Look up a solubility table (like this) and you see that chances are darn low. The best for now is to distill the solvents off (with reduced pressure) which still should be easy (no H2O). For future reference, next time, take a test tube, fill it with some of solvent A and solvent B, shake it, and watch if there is a phase separation within a reasonable time. It doesn't cost much (say 5 mL of each), but guards you against troubles for extraction and TLC. $\endgroup$
    – Buttonwood
    Jul 1 at 17:09
  • $\begingroup$ that table says they are miscible. At least in basic testing, they don't seem to separate within a reasonable time (2h @ 25 C -- Room Temperature). $\endgroup$ Jul 1 at 19:46
  • 1
    $\begingroup$ I just aaded your comment for jimchmst's answer. I think it's important to be in the question. If you don't agree, just roll over. $\endgroup$ Jul 1 at 19:59
2
$\begingroup$

The OP's comment: I'm just using the chloroform to get rid of other compounds, so once I separate it out, I expect my molecule to be in the aqueous phase, and then to vacuum distill it out.

This indicate OP's in the process of isolating a water soluble compound from a (bio)metrix. Probably a natural product. In old days, there was a procedure we have follwed to isolate low polar to high polar compounds. The procedure as follows:

  1. The extract was first dissolved in 90% methanol/water mixture (90:10 methanol:water). This solution is subjected to solvent-solvent extraction with petrolium ether (b.p. $40$-$\pu{60 ^\circ C}$) or even hexanes. Two or three time extraction removes most of non-polar compounds from the initial matrix.
  2. The initial methanol solution is then made upto 75% methanol/water mixture (75:25 methanol:water) by adding enough water. This new solution is then subjected to solvent-solvent extraction with chloroform or dichloromethane. Again, two or three time extraction would remove most of mildly-polar compounds from the initial matrix. The main point here is even in 75% methanol/water, the two layers separate with chloroform. It is true that some amounts of high-polar compounds are also transform to organic layer (here it is chloroform or dichloromethane), yet separation is imminent.
  3. Then again, the initial methanol solution is made upto 60% methanol/water mixture (60:40 methanol:water) by adding enough water. The new solution is then subjected to solvent-solvent extraction with ethyl acetate. Again, two or three time extraction would remove most of fairly-polar compounds from the initial matrix.
  4. Lastly, methanol in the aqueous layer is removed in vacuo and water was removed by freeze-dry method to obtain highly polar water soluble materials.

I think, OP can follow this procedure if OP need only water solubles in the original matrix.

$\endgroup$
3
  • 1
    $\begingroup$ In step #1 why do you add the water first? I would think adding the chloroform first would be beneficial, since you get a solution, as opposed to having to force mix the two phases? $\endgroup$ Jul 2 at 1:43
  • $\begingroup$ My compound if soluble in methanol (and slightly soluble in water). I think I'd just vacuum distill both of them off. $\endgroup$ Jul 2 at 1:44
  • 1
    $\begingroup$ @Sargun Dhillon: To my understanding, I think you have a methanol extract and you want to remove unnecessary organic solubles to get water solubles. I think I was wrong about water solubility. Yet, this method gives you judt water/methanol solubles at the end. $\endgroup$ Jul 2 at 3:50
-1
$\begingroup$

Here is the phase diagram, good luck! Addition of water will eventually give two phases but your extract will most likely distribute between them. Depending on what you were extracting the advice to carefully vacuum distill at very low temperature the solution is the best idea; then I would carefully progressively extract the residue with solvents of increasing polarity to see what extracted. My suggestions are: pentane, methylene chloride, possibly ethyl acetate or chloroform, methanol, [if you are after fluorinated compounds perfluoro-2-propanol] water. Be observant. If done properly this can be the poor man's liquid chromatography.

$\endgroup$
2
  • 1
    $\begingroup$ Please cite illustrations appropriately without links to the search engine queries with irrelevant tracking junk. $\endgroup$
    – andselisk
    Jul 1 at 18:39
  • $\begingroup$ I'm just using the chloroform to get rid of other compounds, so once I separate it out, I expect my molecule to be in the aqueous phase, and then to vacuum distill it out. $\endgroup$ Jul 1 at 19:32

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.