Sciencemadness Discussion Board

NaCl vs. KCl to salt out oganics

FormerBeagle - 17-7-2020 at 12:40

I’ve been told that KCl is superior to NaCl to salt an organic cpd. out of aqueous solution for liquid-liquid extraction. This is for a substance soluble in both water and organic solvents. Is this true, and why? I’ve always used NaCl. Any theoretical reason for using KCl? I remember that the solvation shell of K and Na is different, but just geometrically I think? Not different in number of waters bound. Unsure about that.

Nonexistent - 17-7-2020 at 13:18

Don't quote me on this but as far as I am aware because of the electronegativity and dissociation constants, and KCl being more readily dissociated, matrix effects are more likely to occur due to water being more attracted to the K+ and Cl- ions than Na+ Cl- ions as they want to hold together slightly more, therfore the organics/proteins having less water molecules to be dissolved in. For KCl/NaCl, the numbers are small and a larger amount of NaCl should work just as well.

FormerBeagle - 17-7-2020 at 14:39

Thanks, I’m trying to unravel that. Matrix effects seems to be the correct description for this effect, and I was unaware of that terminology. Dissociation should be complete up to the point of saturation for both salts though, I think. And total ionic strength of the solution should be the most important factor at work here to my thinking. So for ~100% dissociated salts, the one where you can get more into solution should be most effective. So NaCl should be it.

TheMasterOfTheInternet - 17-7-2020 at 14:56

-deleted-

[Edited on 18-7-2020 by TheMasterOfTheInternet]

TheMasterOfTheInternet - 17-7-2020 at 15:11

NaCl and KCl are almost identical when salting out organics from water.
KCl should be slightly better in theory (Potassium salts are generally less solouble in organics than sodium salts end sodium salts are less solouble than lithium salts...) but I can't see a visible difference in practice. I've tried both but sticked to NaCl for "simple cases" aaand...

Potassium carbonate K2CO3 might be the shit you're looking for :D
You can salt-out even extremly well solouble hydrophile substances and solvent like even ethanol and methanol from water for example (NaCl can't do that at all ).
I've tried a few salts (Na2SO4, MgSO4, NaOH, KOH, Na2CO3, NH4NO3, NH4Cl and few more) but that's the best stuff I found so far, several times better than classic NaCl and quite cheap too.

Molecule size and many other effects do matter too next to soloubitly when you want to salt out something, but most important you need a substance which is very highly solouble in water but which but refuses to dissolve in your organic solvent/substant you want to salt-out. Potassium carbonate is insolouble in most coomon organic solvents but dissolves up to 1120g/liter in water (NaCl and KCl both maybe around 350g/liter for comparision) at room temperature so it much more easily and more exhaustive supplants organic molecules from water.

I hope I could help you :)

[Edited on 18-7-2020 by TheMasterOfTheInternet]

FormerBeagle - 17-7-2020 at 16:17

TMOTI: yes, thanks that is a very useful suggestion in general. I will file it away for future use. I honestly would not have thought of using K2CO3 for salting out. Makes sense. More charge = more ionic strength = better salting out. I appreciate you sharing your experience.

Unfortunately there is a lactone present here, so I need to avoid base.

I don’t think of any common inorganic salt as being soluble in organic solvent though, outside polar aprotic. Maybe since there is appreciable water carried into eg DCM or EtOAc, some salt gets carried in as well?

TheMasterOfTheInternet - 17-7-2020 at 17:02

Quote: Originally posted by FormerBeagle  
TMOTI: yes, thanks that is a very useful suggestion in general. I will file it away for future use. I honestly would not have thought of using K2CO3 for salting out. Makes sense. More charge = more ionic strength = better salting out. I appreciate you sharing your experience.

Unfortunately there is a lactone present here, so I need to avoid base.

I don’t think of any common inorganic salt as being soluble in organic solvent though, outside polar aprotic. Maybe since there is appreciable water carried into eg DCM or EtOAc, some salt gets carried in as well?


Which lactone? Most lactones I've played with are quite insensitive to weak anorganic bases like alkalicarbonates, or at least they're only reaction very slowly unless it's hot. So if you wash once with satured K2CO3 it might already do the trick.

Have you though of trying acidic salts ammonium nitrate- or chloride?
I had great success using ammonium nitrate salting out solid inorganic components once, but that was around 2003 so a very long time ago and I don't remember details.

[Edited on 18-7-2020 by TheMasterOfTheInternet]

FormerBeagle - 17-7-2020 at 17:38

Quote: Originally posted by TheMasterOfTheInternet  

Which lactone? Most lactones I've played with are quite insensitive to weak anorganic bases like alkalicarbonates, or at least they're only reaction very slowly unless it's hot. So if you wash once with satured K2CO3 it might already do the trick.


It’s a gamma lactone, existing in equilibrium with the hydroxy acid. So high pH is counterproductive to extraction. Lower pH favors the lactone and better extraction efficiency.
Quote:

Have you though of trying acidic salts ammonium nitrate- or chloride? I had great success using ammonium nitrate salting out solid inorganic components...


Ah, so now you are really onto something interesting! Low pH would help, and ammonium nitrate is super soluble in water. I honestly don’t think I’ve ever used anything other than NaCl to salt out a cpd. That’s why the suggestion to use KCl really got me thinking. NH4NO3 may really help!