poisoninthestain
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small scale solvent stripping
I have 300ml of IPA as my solvent and about 20ml of a desired freebase amine suspended in it. I'm trying to strip off the IPA but since I'm new to
vac distillation this is an alien area for me.
I have a feeling that after about 250ml or so of IPA are stripped under vac(which can pull about 55mmHg) that the rest won't be able to make it out of
the flask.
I understand that short path distillation would be best but the apparatus is too expensive. I only have a 1000ml flask so I'm somewhat concerned.
Perhaps It could be done with just substituting a smaller flask.
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watson.fawkes
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| Quote: | Originally posted by poisoninthestain
I have a feeling that after about 250ml or so of IPA are stripped under vac(which can pull about 55mmHg) that the rest won't be able to make it out of
the flask. |
What would be different at that concentration to change the partial pressure of the IPA? Do you
have an azeotrope to deal with?
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panziandi
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Are you sure it is the free base suspended in it? I would expect an amine to dissolve in IPA. If you have a solid suspended in the IPA then it could
be filtered. If you have two liquids immisible separate them in a funnel. If you mean the amine is DISSOLVED in the IPA you have a couple of options.
Pass in dry HCl to precipitate the amine HCl. Distill the IPA off (bp 82*C) I am assuming that the amine boils much higher since its likely to be a
substituted aromatic compound of some description. Once you obtain your oil of amine then you can apply a vacuum to that and drive off any remaining
IPA.
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poisoninthestain
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sorry, i meant to say dissolved in IPA not suspended. wouldn't titrating the IPA/amine solution also yield isopropyl chloride?
i was under the impression that distilling small amounts in a 24/40 rig wouldn't work for some reason. Now that I think about it, I think the only
problem would be if I were to distill the amine freebase which might result in mechanical loss since it's such a small amount. Again, I don't have
much experience with these two things:vac distillation and small amounts.
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DJF90
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The acid base reaction between the HCl and the amine is very fast, whereas the nucleophilic subtitution of the alcohol is a much slower reaction. So
long as no more HCl is passed in once precipitation has ceased then there should be no 2-chloropropane formed.
Once your amine hydrochloride crystallises out, you could use vacuum filtration to remove the solvent? This would eliminate the need for you to have
to struggle with distillation.
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Jor
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I think (but I'm not sure!) no isopropyl chloride will form at all, as HCl is not acidic enough to protonate the -OH group, and thus no water can
split off, and no attack of the chloride on the resulting carbocation.
You need a Lewis acid catalyst such as ZnCl2 to make it work.
HBr and HI are strong enough though.
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turd
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| Quote: | Originally posted by poisoninthestain
i was under the impression that distilling small amounts in a 24/40 rig wouldn't work for some reason. Now that I think about it, I think the only
problem would be if I were to distill the amine freebase which might result in mechanical loss since it's such a small amount. Again, I don't have
much experience with these two things:vac distillation and small amounts. |
???
You're not distilling, you're stripping a solvent. Just leave it on the pump for a few hours while heating it on a water bath. Stir if your freebase
is a liquid, add a cooling trap if using a rotary vane pump. Simple.
Or just isolate the hydrochloride as described in the literature a bazillion of times.
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