Gassing sucks, this is a axiom as certain as the second law of thermodynamics
There has been various discussions on how to prepare anhydrous HCl in IPA or ether. None of these where really succesfull without gassing at some point. Sometimes its possible to crash out the salt with aq. HCl in IPA and acetone, but it often fails. Lately I have
1 devised a sure fire way of making bone dry chlorides of the precious amines, without gassing. The method takes advantage of the azeotrope formed when distilling a light non-polar mixed with water. Here is how its done.
Once the final amine has been isolated (predrying of the NP prior to the stripping is not even necessary), it is weighted. From this weight the molar amount is calculated. Add an equal molar amount of aqeous 10% HCl
2 dropwise while stirring heavily.
From here, there are two ways to go depending on what equipment you have at hand. The optimal setup is using a Dean Stark trap, but a normal distillation setup will suffice.
The Dean Stark way:Add twice the volume of the water / amine phase of toluene or xylene to the flask. Attach a Dean Stark adaptor with a condensor on top. Start refluxing, untill no more water comes over. Once the water is gone, keep distilling off the toluene or xylene (keep the temperature below 150°C at all times to avoid hurting the amine). The stop cork of the trap can simply be opened and the solvent drained directly into a new flask. Wash the NP with brine and save it for future drying runs
3. The remains of the method is identical for both ways, so skip the next paragraph if using this method.
The ghetto way:If using toluene, add 10X the volume of the amount of 10% HCl you used. i.e. if 10 mL's 10% HCl was needed for the neutralization, add 100 mL toluene. This is a healty 100% excess of what theoretically is needed to dry it, but better be sure. With xylene a little less is required; 6-7X the volume should suffice. Rig the flask for simple distillation. Stirr the mixture
heavily and heat. Distill of as much of the xylene / toluene as possible, without going over the B.P. of the solvent. Save the flask with the amine in it and proceed as described in the last section. The toluene / xylene can be reused. Pour the distillate into a sep. funnel and discard the lower water layer. Wash the toluene / xylene once with brine, and its useable for drying again
3.
Final work:Once most of the solvent has been stripped (if you are very keen on getting all of the solvent of, use vacuum for the last bit), disconnect everything. Let the amine salt in its liquid form cool down and then add a bunch of acetone. Usually 5-10X the volume of the amine is fine. Place it in the freezer and within a few hours crystallization should be complete. In one run i had to scratch the inside of the flask with a glass rod to induce crystallization; but for the "normal" compounds this shouldn't be neseccary. Filter the crystals and recrystallize untill it's pure enough
Summa summarium:
No gas, no water causing oiling out, no problems It sounds like a lot of work, but once you get the hang of it, it's way easier than gassing etc.Notes:[1]
Barium has suggested the use of azeotropes for completely drying various substrates before, so alot of the credit goes to him!
[2]
I chose to use dilute acid, in order not to hurt the amine by local "over-acidification".
[3]
The toluene I reuse for this purpose is
only used for drying. The purity of the isolated distillate is fine in this context - but for other purposes I am not sure. So simply keep a flask of 500 mL's "drying tolly" standing around - it will last a
long time.
Regards
Bandil