Sciencemadness Discussion Board

Post-reaction workup of diisopropylethylamine

TD64209 - 13-9-2019 at 18:03

24hrs after refluxing EtI and iPr2NH, and seeing the DIPA-HI precipitate, there is still a small layer of liquid amongst the precipitate, under the MEK layer.

Any ideas what this liquid is? I'm assuming it's free DIPA as I did use a slight excess, which messes with the written workup.

Should I just

A: Distill off all volatiles, add fresh MEK, and proceed as normal? Is DIPEA-HI actually soluble in MEK?
B: Leave the DIPA-HI and DIPEA-HI residues combined, and fractionally distill the mixture of amines after raising the pH and separating the mixed amines from the alkaline H2O?

Tsjerk - 13-9-2019 at 23:16

Could you be more specific?

24hrs after refluxing EtI and iPr2NH, and seeing the DIPA-HI precipitate, there is still a small layer of liquid amongst the precipitate, under the MEK layer.

Any ideas what this liquid is? I'm assuming it's free DIPA as I did use a slight excess, which messes with the written workup.

You can't assume we all know this procedure and know what happens and how it looks.

Start by posting a link to the procedure you used.

[Edited on 14-9-2019 by Tsjerk]

TD64209 - 14-9-2019 at 10:23

No I wouldn't expect that, but I figured it was a simple-enough reaction to not be necessary.

I used Scr0t's write-up as a rough guide for comparing yields:

Same solvent (MEK) used, same molar ratio, with the exception of a few extra grams of DIPA base.
77.85g DIPA needed, ~84g was used (naively) for simplicity (Didn't wanna separate off the extra few grams for pain-in-the-ass storage of miniscule amounts).
I would've added extra EtI to compensate, but ran out.

Edit: My dominating hypothesis is that the suspect liquid is just free DIPA that had no HI to neutralize. It's density is less than MEK, though, so it's tendency to sink I can't explain. Attracted to the DIPA-HI salt?

[Edited on 14-9-2019 by TD64209]

Tsjerk - 15-9-2019 at 05:04

Yes, simple enough when you know it ;)

I would just filter and wash with MEK. Apparently that is the only seperation Scr0t used to get to the iodide salt, and did so in good yields.

I don't know what your liquid phase is. But I also don't really understand what you mean. Do you have two liquid layers or do you have some liquid? I guess two layers.

That is strange as everything except the salts should be soluble in MEK.. I would filter, wash with MEK and distill.

Do you have a planned use for the amine? Nice compound to have!

TD64209 - 15-9-2019 at 13:50

Yeah ego will kill it every time. :P

For clarity:

Pre-reaction - One single phase, consisting of DIPA, MEK, and EtI all dissolved together.
Post-reaction - An upper MEK layer, a small (15ml ish) liquid layer below that, and then a pile of presumed DIPA-HI crystal.

Scr0t's write-up states that the solid is DIPA-HI (not DIPEA-HI), which leads me to ask this question:
Is DIPEA-HI soluble in MEK?

The amount of liquid in the lower layer looks to be only around 15ml, which would add up perfectly to how much excess DIPA freebase I added in the beginning.
So after everything reacted, and both the DIPA & DIPEA neutralized the HI, I think it's just DIPA freebase that had no HI to react with. There's still an ammoniacal smell to the mix.

Tomorrow I'll probably take action, hotplate's busy today.

Edit: Yep, unless I'm in the mood to whip up some triethylamine soon, then this'll be used as a non-nucleophilic base in a separate alkylation of primary amines to tertiary amines; hopefully avoiding quaternary salts completely. ;)

This is the first time I've made/had DIPEA, and can't think of a better use (for my interests).

[Edited on 15-9-2019 by TD64209]

Tsjerk - 16-9-2019 at 08:02

My guess is that both DIPA-HI and DIPEA-HI are quite insoluble. I think that your precipitate is an mixture of both, and that the ratio depends on how big your surplus of DIPA was.

That would also mean your DIPA layer contains some DIPEA. I don't know why it separates from the MEK. Maybe it is being sort of salted out.

I think work up a s usual with a distillation would be nice to separate and you can maybe push the yield a bit by adding a bit of sulfuric acid so you can recover the freebase as precipitate and not lose it while filtering.

I would try not to overshoot with the sulfuric as I think the bisulfate is a lot more soluble.

Are you sure the reaction was dry? I can imaging water would aid in the seperation.

[Edited on 16-9-2019 by Tsjerk]

TD64209 - 18-9-2019 at 16:56

I think it must've been at least partially water, because it nearly vanished after sitting in the freezer.

Precipitate vac filtered, filtrate treated with aq HCl, distilling off MEK & H20 as I type. It looked and smelled like some amine was boiling under vacuum while filtering, so it was done in "pulses".
Evolved gas during HCl addition got a bit wild (accidentally fogged the room adding it while open-air, so finished adding the rest dropwise via funnel in sealed distillation.)

Once the filtrate's concentrated, will neutralize residue w/ NaOH and separate, then distill.
Will get dry weight of previously filtered precipitate soon.

Dr.Bob - 19-9-2019 at 04:55

A trace of water will dissolve some of the salts and create anothet layer. Might want to dry the MEK with Na2SO4 ot the like before the reaction, as well, the DIPA could be distilled from KOH to dry it. Or just try to evaporate the water from that layer once it is separated and get the salt back, but that will be tough, as amine salts are hygroscopic as can be. Or just basisify and extract and distill it, a trace of water there is harmless.

TD64209 - 20-9-2019 at 06:39

Yields are in:
63.18g of filtered precipitate, presumed DIPA-HI, slightly clumped after sitting out overnight after drying on the pump.
~65-70ml of NaOH-dried, not-distilled, isolated amine; presumed DIPEA freebase.

This would mean there's an unaccounted-for few mls of DIPA freebase, which I assume boiled off (BP 84'C) during the vacuum filtration.

A question:
Would this semifinal product effectively serve it's purpose (mentioned up-thread) without distilling? It's golden yellow, transparent, and my glass isn't optimal at all for high-efficiency with micro amounts. I may still do it using my smallest flasks (100&50ml rbf) but my "column" is just a straight tube Liebig-style, and condenser is actual Liebig. 'Synthware'