Sciencemadness Discussion Board

Making iPrOH:NH3:H2O Anhydrous

Newton2.0 - 8-2-2022 at 21:40

So, I was aiming for iPrOH:NH3 using the known method with a minor modification so please give me some insights into this procedure:

1) 59g (1 mole) KOH in 150mL dH2O in a 500mL addition funnel set atop a straight 24/40 straight gas outlet adapter atop a 1L boiling flask with a stirbar on a heating mantle.

2) 54g (1 mole) NH4Cl dissolved in 200mL store-bought ammonia (the idea being that some additional NH3 would boil off)

3) PTFE tubing from the gas outlet leads to a cylindrical container filled with anhydrous iPrOH and a magnetic stirbar to increase absorption.

4)After heating I noticed NH3 generation, however, I had a bad system and didn't scrub H2O from the gas.

My question is how to remove H2O from the solvent system, and I have a few ideas:

1) Addition of CaCl2 and let it sit for a bit, then redistillation well below the BP of H2O so I get only the NH3:iPrOH (do I need to add more KOH due to the formation of NH4Cl upon addition of CaCl2 and then the Ca(OH)2 precipitate remains)

2) Bad idea: Add 3A/4A Molsieves to the container and remove both water and NH3 from the system. (Yes, I know NH3 is taken up by these sieves, so loss of product is acceptable, but not optimal).


Jenks - 9-2-2022 at 08:37

CaCl2 is acidic so it would take out the ammonia just like sieves would. Potassium carbonate forms a separate layer if there is a lot of water, so that could be separated and the top layer distilled, but I think that would only take it to 99%.

[Edited on 9-2-2022 by Jenks]

Tsjerk - 9-2-2022 at 10:09

Sieves wouldn't work as there is more NH3 than water, when if it was the other way around you would have to add the sieves multiple times as you would get an equilibrium of water / NH3 in the sieves.

CaCl2 is not acidic, should work, as well as K2CO3 or MgSO4 or Na2SO4.

I don't know how clean you need your solution, but if you can just filter I would go for that, as the ammonia probably will boil out of solution, so you would need to catch the gas again.

SWIM - 9-2-2022 at 10:48

Calcium chloride is fairly soluble in the lower alcohols.
Didn't find specific numbers for isopropanol but you might want to check for that.

I think you'd be better off in the long run just re-doing the whole thing with a better method of drying your ammonia.

If you do want to try drying this solution, how about calcium oxide? It's pretty good at scavenging water from lower alcohols.

I agree with Tsjerk that distilling would boil off the ammonia.

I used to make ammonia/alcohol solutions by just dumping ammonium sulfate and potassium hydroxide in the alcohol and sealing it in a strong container kept cool for a couple of days.
Assuming the potassium sulfate generated would absorb the water created.

This seemed to work okay as a basic solvent for some extractions from natural materials, but I never tried it for anything water content critical like doing an SN2 reaction on a brominated allylbenzene.

Amos - 9-2-2022 at 12:55

Maybe try running the gas up a long, ice-cold condenser and then running it into the bottom of a makeshift drying tower consisting of some tall ground glass jointed container with coarse pieces of anhydrous sodium sulfate piled up in it. Then you could bubble the dried ammonia gas through a suckback trap and into your isopropanol.

Newton2.0 - 9-2-2022 at 13:40

Great, thanks for the feedback! I will use a suitable drying agent and filter!

DraconicAcid - 9-2-2022 at 19:19

Why would you use so much water in your initial setup? Surely it would be better to slowly drip a concentrated solution of KOH onto a dry or barely damp sample of ammonium salts. That would give you far more ammonia with less water vapour.

AvBaeyer - 9-2-2022 at 19:43

Do your experiment over You will not be able to dehydrate your solution wthout considerable loss of ammonia. DraconicAcid is correct. When you generate your ammonia, pass it through a column of sodium or potassium hydroxide pellets to dry it.