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Author: Subject: Dimethylamine storage
Pumukli
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[*] posted on 16-7-2017 at 08:13
Dimethylamine storage


Dear all,

I would like to save some dimethylamine from wasting as a herbicide component and thought that I should distill it out with the help of a strong base instead. ;)

Question is what should I do to store it? I envisioned some nice crystalls in a jar but I'm not sure which anion wold be the best for that porpuse. Chloride salt of dimethylamine is hygroscopic as I heard.
I would like to use an acid with which the formed salt would be non-hygroscopic, has a fair solubility in water and preferably crystallizes without crystal-water. The smaller the molecular weight (or equivalent weight) the better.
Suggestions?
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Eddygp
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[*] posted on 16-7-2017 at 13:48


Maybe dimethylammonium tetrafluoroborate, as long as you have access to it? In principle, any of its simple salts should be very soluble in water, unless you use some weird 161-carbon chain acid.

Halogens will probably not get what you need. What about coordinating it to a metal or something and storing the metal as a salt? Probably much more complicated, but nice and exotic crystals!




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zed
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[*] posted on 17-7-2017 at 18:32


Ummm. Dimethylamine free-base used to be available in sealed glass ampules. It's a low boiler, so sealing is a must.

Nothing wrong with storing it as the Chloride salt. Or perhaps, the Sulfate. Just use an airtight jar.

Just capture your free base in an anhydrous alcohol, and gas it with HCl....or, treat it with H2SO4. But, perhaps I am hasty!

I'll check Vogel for pointers. I'm not too sure about solubility of salts, now that I think about it.

"111.118, D1METHYLAMINE HYDROCHLORIDE
Proceed as in the preparation of methylamine hydrochloride (previous
Section) using 200 g. of ammonium chloride and 400 g. of formalin, and
heat the mixture at 104° until no more liquid distils. Cool to room
temperature and filter off the ammonium chloride (ca. 50 g.) : add 300 g.
of formalin to the filtrate, return the solution to the distilling flask, heat
until the temperature reaches 115° and maintain it as nearly as possible
at this temperature until no more liquid passes over (about 3-4 hours).
Concentrate the residue in the distilling flask on a water bath until a
scum appears on the surface of the hot liquid. Cool to room temperature
and filter off the solid (ca. 32 g.; impure methylamine hydrochloride
containing about 25 per cent, of ammonium chloride). Pour back the
filtrate into the distilling flask and heat to 120° until a sample of the
liquid, on cooling, becomes semi-solid. Transfer it to a vacuum desiccator
charged with sodium hydroxide pellets and leave it there for 2 days.
Extract the residue with hot chloroform and filter ; on cooling, crystals
of dimethylamine hydrochloride separate. A further crop can be obtained
by evaporating the filtrate to about half its original volume. The yield
is 120 g."

Ummm. Vogel suggests crystallizing from hot Chloroform....and drying in a vacuum desiccator. I don't like that idea.



[Edited on 18-7-2017 by zed]

[Edited on 18-7-2017 by zed]
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Melgar
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[*] posted on 19-7-2017 at 05:03


Quote: Originally posted by Eddygp  
Maybe dimethylammonium tetrafluoroborate, as long as you have access to it? In principle, any of its simple salts should be very soluble in water, unless you use some weird 161-carbon chain acid.

I just read a bit about tetrafluoroborates, and they're not actually as exotic as I thought. Granted, I live in Manhattan and work in the garment district area, but I've seen multiple places that sell hydrofluoric acid, (you can barely read the main label with all the warning labels on the bottle, so you can be sure it's the right stuff ;) ) Not highly concentrated (~10%?), but it wouldn't have to be, since apparently it's one of the most inert ions that exists with a -1 charge after HF reacts with boric acid and the resulting tetrafluoroboric acid is neutralized.

Of course, that would be overkill, since I see no reason that the sulfate salt wouldn't work, and that's what's used to stabilize hydrazine.




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Pumukli
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[*] posted on 21-7-2017 at 11:00


Thanks for the tips guys!

Mentioning "nice crystalls" may misled some of you though!
I think the tetrafluoroboric acid would probably make some nice, well-defined non-hygroscopic crystalls but it would be overkill for my real aim: I want to store dimethylamine as a solid and be able to release it when I need some!
Chloride would be the obvious choice but it makes a hygroscopic salt and I don't want to recryst. from chloroform and use a vacuum desiccator (Vogel) just to postpone the obvious end: some sticky mass in a jar that once was nice powder. :-)

What I did so far: tried to distill some dimethylamine (DMA) from the herbicide. It did not went too well, I obtained some 30% yield, although the scale (5 g) was too small for my equipment and I learnt some insight on how the actual distillation goes. Based on these observations I can/will improve the next try.

What I want to achieve first is some fairly pure DMA as aquaeous solution. Then I plan to make a series of neutralizations in a 0.5g scale with different acids. Organic acids and inorganics as well -what I can find among my chems- and evaporate the water from each in a petri dish. The hygroscopic ones will fail to dry, but I hope that I will be able to find at least one which yields some nice crystalls or at least a non-hygroscopic dry powder without resorting to vacuum desiccation. :-)

I know I could store the distilled solution too but somehow I prefer a dry powder to a smelly, corrosive liquid. :-)
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Pumukli
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[*] posted on 26-7-2017 at 01:03


I've tried eight different acids so far. The results were interesting so I'm planning to run a quick and dirty "challenge" for you all. :-)

Basically all you should do is to predict which acid produced which result (selectable from a few different answers).

I'm still waiting for two more acidic compounds to test and thinking about the prize for the winner. :-)
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