Monoamine
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Methylamine sulfate vs. methylamine HCl vs. methylamine freebase
I just have a quick question about the different salts of methylamine. I'm trying to prepare a small quantity from sulfamic acid with methanol. This
is a quite streight forward and easy method where the sulfamic acid reacts with the solvent methanol to form ammonium methylsulfate, which rearranges
at around 230C to form methylamonium sulfate.
So my question is: since methylamine is most often encountered in the HCl form, is there any real advantage of converting it to the HCl salt from the
sulfate salt? This could be done by liberating the freebase with NaOH and then bubbling the methylamine freebase gas into conc. hydrochloric acid.
But why bother to do this?
Also, what about if you want a methanol solution of freebase methylamine? Is it efficient to just slowly drip a concentrated solution of NaOH into the
methylamine sulfate to liberate the freebase and then to bubble the freebase into methanol? Or will a lot of the methylamine get lost that way?
[Edited on 6-7-2024 by Monoamine]
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Fery
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Maybe if you add methanolic solution of NaOH to methylamine sulfate then Na2SO4 crystallizes out due to low solubility in methanol? Just from my head,
should be tried practically. If that works then no need to work with gaseous freebase.
solubility of anhydrous Na2SO4 in methanol: http://chemister.ru/Databases/Chemdatabase/properties-en.php...
g / 100 g solvent
methanol: 0.01 (10°C)
methanol: 0.017 (20°C)
methanol: 0.018 (30°C)
methanol: 0.02 (40°C)
methanol: 0.019 (50°C)
But at first you need to purify methylamine sulfate. It seems to be quite impure when obtaining it by heating ammonium methyl sulfate at 250-280 C,
see the video between 7 and 10 minute, they distilled out the amine anyway:
https://www.youtube.com/watch?v=EtQOgDY6wdQ
It would be nice to know a solvent for purifying / recrystallization of methylamine sulfate. For hydrochloride they used absolute ethanol in first
round and then 1-butanol, see the "note 4" here:
https://www.orgsyn.org/demo.aspx?prep=CV1P0347
| Quote: | 4. Since ammonium chloride is not absolutely insoluble in 100 per cent ethyl alcohol (100 g. dissolve 0.6 g. at 15°), the methylamine hydrochloride
purified in the manner described contains appreciable traces of it. A purer product can be prepared by recrystallizing from n-butyl alcohol, in which
the solubility of ammonium chloride even at the boiling temperature is negligibly small. Methylamine hydrochloride is somewhat less soluble in this
solvent than in ethyl alcohol, but as a rule three extractions carried out at 90–100° with 4–6 parts of fresh butyl alcohol for each extraction
result in a substantially complete separation. Since the last traces of the solvent are not readily removed by exposure to air, a solution of the
recrystallized material in a small quantity of water should be distilled until free of alcohol, and allowed to crystallize.
An entirely different method for preparing pure methylamine hydrochloride free of ammonium chloride has been described.1 It is based on the fact that
when a mixture of methylamine and ammonia reacts with an insufficient quantity of hydrochloric acid the methylamine is preferentially neutralized and
the ammonia left free. |
Personally I would use Soxhlet extractor instead of 3 extractions.
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Monoamine
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Thanks for the reply Fery. This is very interesting. Especially the comment at the end about methylamine prefferably being neutralized by HCl than
ammonia. So maybe having a series of wash bottles with HCl through which the gas is passed will create several "fractions", where the first fraction
will be the most pure methylammonium chloride and the last fraction will contain the most ammonium chloride.
Still, I only expect a lot of ammonium in there if the rearrangement of ammonium methylsulfate to methylammonium sulfate is inefficient.
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Fery
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I found this, they prepared methylamine that way and added (NH4)2SO4 during heating to reduce dimethyl and thimethyl side reactions
https://www.tesble.com/10.1039/ct9201700236
Attachment: ct9201700236.pdf (661kB)
This file has been downloaded 29 times
That introduces ammonium sulfate but it could be perhaps separated by extracting methylamine sulfate using Soxhlet and methanol as (NH4)2SO4 is
insoluble in methanol. I did not find solubility of methylamine sulfate in methanol.
http://chemister.ru/Databases/Chemdatabase/properties-en.php...
1:1 molar mixture of ammonium methyl sulfate : (NH4)2SO4 was able to still melt completely, but twice amount of (NH4)2SO4 already left undissolved
(NH4)2SO4
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Mateo_swe
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The reasons of converting methylamine from the freebase would be storage problems.
Methylamine freebase is a gas so storage is rather difficult like this.
One can bubble methylamine gas into icecold methanol and store it like a methanolic solution of say something like 40%.
Or convert it to the HCL salt, this is the way it´s often sold.
But methylamine HCL is very hydroscopic and picks up moisture from the air very quickly so one needs to be quick or find a good procedure.
The sulfate salt i have never seen, maybe there is a reason for this.
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woelen
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Why would you want to convert methylamine to a salt? I have methylamine 40% in water. It stores perfectly well in a glass bottle with a decent cap. It
is not particularly corrosive, nor giving off fumes through the cap. You just need a bottle with a sturdy plastic cap, which tightly closes the
bottle. At 40% concentration, there is no or only minor pressurizing in the bottle, not even in summertime at 30 to 35 degrees Centigrade.
I also have methylamine HCl, but as told already, that is very hygroscopic, and my solid is somewhat humid. The crystals stick together.
I can imagine, that storing methylamine as a solution in methanol or ethanol also works fine. I never tried this myself though, I only used it in
experiments in aqueous solution.
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Fery
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Wow this is my 1000th anniversary post 
So I did a quick try of the reaction between methanol and amidosulfonic acid into ammonium methyl sulfate.
97,1 g of amidosulfonic acid (1 mol) with 200 ml of methanol was put into 500 ml RBF and magnetic stir bar. The methanol used contained only very
little of H2O (max. 0,05%), its volume was in excess but later the volume shown to be the right amount. Reflux condenser was attached with drying tube
to prevent moisture from air to enter. The reaction was heated and magnetically stirred. The reflux lasted totally 6 hours from which first 3 hours
the stirring was impossible and only after 3 hours when substantial amount of sulfamic acid reacted the stir bar started to rotate finally.
After 6 hours of reflux (from which 5 and half hours there were visible crystals and only last 30 minutes the content was fully dissolved) the heating
was stopped and the content was allowed to cool down to room temperature. The solution stayed clear due to its supersaturation. Only after vigorous
stirring for few minutes the supersaturated solution crystallized quickly. The condenser was detached, flask was stoppered and put into a fridge to +4
C overnight.
Crystals were filtered on sinter, dried for a while on sinter using suction (it was necessary to press them into about half of their volume using the
reversed side of a stopper, also take in account they are hygroscopic so do not suck them for too long) and then further dried in a desiccator over
anhydrous CaCl2. Crystals were very fluffy, their volume was about 200 ml when scraping them from sintered funnel.
Mother liquor was put back into 500 ml RBF and 100 ml of methanol was distilled out. The same crystallization process was repeated and the crystals
(cca 3 times less than the main crop) were added to the main crop and dried in desiccator. From the second filtration the volume of mother liquor was
30 ml so approximately 50 ml of methanol was lost during vacuum filtration + adhering on the crystals or maybe forming some adduct. The product was
hygroscopic which was visible on their remainders when cleaning the glass.
All the excess of methanol could be just distilled out instead of crystallization but then you have to quickly pour out the product from the
distillation flask to a dish with aluminium foil while it is still hot before it solidifies (see the ChemPlayer video).
methanol, very low water content (max 0,05%)
amidosulfonic acid (if using not much pure acid especially with insoluble impurities then very likely no supersaturated solution obtained)
reflux, a lot of acid on the bottom of flask which denied stir bar to rotate for half of the reaction time
after 3 hours of reflux a lot of amidosulfonic acid reacted so the stir bar started to rotate finally
after 5 hours of reflux there was still a little of undissolved amidosulfonic acid, it completely dissolved after further 30 minutes and the reflux
was done for 6 hours totally
vacuum filtration of the product
distilling out 100 ml of methanol from the mother liquor (stirring stopped for a short time just to make a photo)
second crop of the product
crystals were quite fluffy and hygroscopic
references:
https://www.bitchute.com/video/Ian9ZMFBM3bL/
https://seed131.bitchute.com/2vWmMgSEZ2jf/Ian9ZMFBM3bL.mp4
https://www.youtube.com/watch?v=zU9qJRfISIk
methylamine from the ammonium methyl sulfate:
https://www.youtube.com/watch?v=EtQOgDY6wdQ
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