Author Topic: Preparation of anhydrous MeNH2 / HCl etc.  (Read 2744 times)

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Bandil

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Preparation of anhydrous MeNH2 / HCl etc.
« on: September 02, 2004, 04:25:00 AM »
Hi there!

While being in dire need of anhydrous methylamine, HCl, ammonia, etc. in some kind of non-polar solvent I have pondered some options:

1) Azeotropical preparation of anhydrous methylamine in diethylether or toluene

The first idea for preparing anhydrous methylamine in ether and/or toluene/xylene, was using azeotropical distillation of a proper NP and aqeous methylamine. The obvious question is whether the methylamine will distill with the azeotrope and simply stay in the discarded water layer or stay in the NP and work as advertised? Anyone know how methylamine behaves under these kinds of temperatures?

2) Anhydrous methylamine by simple drying

Another obvious choice would be to mix the NP with the aqueous methylamine and dry it with a cheap agent such as sodium sulfate. For a one mole run the stats would look as the following:

1 mole methylamine
Mass 40% MeNH2 = 72.5 g
Mass MeNH2 = 29 g
Mass water = 43.9 g
Mass Na2SO4 ~ 50 g (assuming 1.2 g/g drying capacity)
Mass Xylene / Toluene = 350 g /assuming the solubility is 10% w/w of the methylamine.

This slurry would be stirred for some time and the drying agent filtered off. I suppose some of the methylamine would be lost in the drying agent. But assuming a 50%+ yield could be expected, I'd go for the method. Final drying is done with sieves.

3) The same methods with HCl

The exact same schemes as stated above... Would it make a difference?

4) Final notes + questions

What is the solubility of methylamine in ether? I've been quite unable to find this anywhere. Also, how does temperature affect the solubility of the gas in the non polar solvent? Will raising the temperature give off vapours or will it increase the solubility?

Hope you can provide me some answers  :)

Thanks, regards
Bandil


indole_amine

  • Guest
azeotropic distillation
« Reply #1 on: September 23, 2004, 10:02:00 AM »
Hi!

At higher temperatures, gases (like methylamine or HCl) have a smaller solubility in solvents than at low temperatures, hence you have to cool your solvent when gassing compounds into it. So azeotropic distillation would not only remove the water but also the needed gas. :(

But this azeotropic distillation technique is very well suited for crystallization of amine hydrochloride salts: simply dissolve your amine in low-boiling nonpolar (preferably one which distills azeotropically together with water  :) ), add equimolar amount or better slight excess HCl 37%, distill solvent away. If the solution doesn't become cloudy, add again same amount of solvent and repeat until your solution becomes cloudy/milky. Then pour into beaker and place it into the freezer for 2 days, or alternatively add 2x the volume in anhydrous acetone, and chill just for several hours, then you can filter off the precipitated hydrochloride and rinse with cold, waterfree acetone (and don't forget to dry to constant weight, of course).

For anhydrous methylamine, try the following: dissolve aequous methylamine 40% in prechilled solvent of choice (MeOH or iPrOH work well, toluene may also) and add enough drying agent to soak up all water present. Important here is that you choose a drying agent being inert to methylamine/HCl/{all your other gases} AND inert to the solvent. A good one for methylamine would be molecular sieves 3A, good for HCl is CaCl2 for example - but these two react with alcohols (molecular sieves like 4A and higher have the capability of soaking up EtOH, while CaCl2 reacts with all alcs). Also important is that you use enough solvent to take up all gas and that the solvent is cold and dry.

indole_amine

r2e3

  • Guest
maybe
« Reply #2 on: September 23, 2004, 04:24:00 PM »
i am being contentious

but this didnt make much sense apart from being overly technical - for want of a better expression

in principal - yes - gases have better solubilty at low temps

apart from that - i am at a loss

indole_amine

  • Guest
assistance
« Reply #3 on: September 25, 2004, 10:31:00 AM »
Why at a loss? Just continue with your logic: gases have also a lower solubility at higher temperatures.

And therefore, distillation isn't possible without releasing the major part of the dissolved gas.


But making anhydrous MeAm or HCl in ether/IPA/whatever is possible with molecular sieves or other drying agents, because the solvent stays cool and mucho gas can dissolve in it...

Methylamine/IPA (example)
Just add 87 ml of commercial 40% aequous methylamine solution to, lets say, 360ml IPA in a flask, then add 230g DRY molecular sieves 3A, quickly cover with foil (or even better: use a flask with screwable lid!) and let stand in the fridge for several days (longer is better here, sieves work slowly in the cold). Now filter off the sieves, and you have something around 360ml (or ~300 grams) of nice anhydrous 10% methylamine/IPA solution (all percentages are weight/weight).

For making anhydrous HCl, you have to use acid-resistant drying agents that DON'T react with primary amines and/or alcohols (search rhodium's site for "drying agent selection") - but it works the same way as described...

Hope this was easy enough.  :P


indole_amine

pooky

  • Guest
Explain please...
« Reply #4 on: September 25, 2004, 11:12:00 PM »
The first time P tried gassing MeNH2 gas into ice cold MeOH (-25C) there was nothing but huge bubbles passing unmolested through the Methanol, and up the exhaust.After reacting 100g MeNH2 and seeing only a 5g gain in weight of the methanol(and most of that was ice crytals on the flask taking the moisture out of the air)P bought a gas diffuser and a skinny 2 foot tall glass vase.The results were only slightly better,with 80 % or more of the tiny bubbles making it to the surface.P then thought to try the methanol at 50C...the results were much better.Then came 55C when the MeNH2 gas coming out of a 1/2 inch tube would form a flame shape from the tube tip,with not one bubble of gas escaping more  than the "flame".It sounded like a  spitting cat,with pops and cracks.P is sure that it will be pointed out that some of the MeNH2 is boiling off,but in reality very little actually makes it out of the flask:P checked.It beats  having it blow straight through.
That was long ago,but this would be good for the one time Bee,could get 50g freebase MeNH2 in about 15 minutes of slow going.Dry your gas with CaCl2,and your now chilled methanol with indicating silica gel.P graduated to antifreeze and gas traps, but that is another story..

The gas is quite warm,as you point out.Please explain how the gas is supposed to cool from 50-60C to -6C in a fraction of a second in -20C methanol,like it is said to do.Thanks..P :)


hest

  • Guest
bubbles
« Reply #5 on: September 26, 2004, 03:08:00 AM »
gass throug those small airbubbler stone you can by in ewerye aquarium shop in the world for a quater (you know that cool coin they have in the states wee use in that stupid beerdrinking game  ;) )

indole_amine

  • Guest
slow gassing may also help
« Reply #6 on: September 26, 2004, 09:27:00 AM »
Just make sure your bubbling stone is base/methanol-resistant and doesn't start to dissolve while you're gassing... ::)

About cooling the methylamine(g) prior to bubbling it through solvent (may I quote Terbium at this point):

"Calcium chloride will definitely absorb the methylamine or any amine. I would be wary of silica also. NaOH pellets would be best for drying methylamine gas. Bubbling the methylamine gas through a saturated NaOH solution should also work. You can even get away without any drying if you let the gas cool through a long neck flask or reflux condensor."
terbium


As for the temperature: I don't believe that methanol at 55°C can take up more gas than at lower temperatures. Especially not if you heat MeOH almost to its boiling point. Most likely the gas was made too fast and/or bubbled too fast.
Gases simply have a lower solubility at higher temps. Thats a fact.

So the error most likely wasn't the temperature of the methanol but rather something else...
(try gassing at such a rate that bubbles only appear every 20-30 seconds, and prepare to wait hours before it is finished)

And don't gas into an open vessel like a beaker: better use a 2-neck flask with a condenser in the main neck and bubbler tube in side neck. The methylamine won't dissolve completely while bubbling through the methanol, but will make a methylamine(g) atmosphere above the MeOH surface and slowly migrate/dissolve into it. Only important thing is that the vessel you use can hold back gases, and doesn't allow them to escape directly after leaving the MeOH as bubbles. Therefore the 2-neck RBF and condenser.

Good example for proper gassing setup:

Post 503373

(r2e3: "MeNH2 gas from MeNH2.HCl using NaOH", Newbee Forum)



indole_amine

moo

  • Guest
Gas dissolution
« Reply #7 on: September 26, 2004, 05:12:00 PM »
It might be that the rate at which the methylamine dissolves in the methanol is slow enough to cause problems at -25°, not that methanol would hold more gas at 55°. Just a theory, haven't really studied the subject yet. I suppose there is an explanation for the observation.

If the MeNH2 gas is too warm for ones taste, one might pass it through a condenser, maybe even a spiral condenser.


pooky

  • Guest
Try It..
« Reply #8 on: September 27, 2004, 05:36:00 PM »
if you don't believe it.Stirring rapidly, single bubbles in -20 methanol make it to the top,with the diffuser being only slightly better.

P's experiment:started with -20C 100g methanol,measured the temp continuously,and gassed until the MeNH2 uptake was perfect(the gas warming up the methanol-growling noises with spits and pops)The temp was 55C.Can always see the MeNH2 freebase "swirlies",and it took 10 minutes for 5 grams of the MeNH2 to evaporate out of the flask.When you are done,top it with tissue and pop into a bucket of -20 antifreeze.

If one has to wait 20 to 30 seconds for each bubble,it will take weeks to get a couple kilos of freebase :(
Without a large (8cm X 3meter)coil condensor with traps,antifreeze,dedicated freezer etc, gassing MeNH2 works best warm,end of story.Try it.
Perhaps study solvents,and how temperature affects their abilities.
P thinks all this got started from LaBTop's write up on the borohydride reduction (P loves LaBTop)but LaBTop had tanks full of liquid methylamine.

P is on holidays for a week or two.

P challenges anyone to try it and report back....


indole_amine

  • Guest
Perhaps you might want to consult the merck...
« Reply #9 on: September 28, 2004, 07:24:00 AM »
Hey, you "master debater": Perhaps study solvents,and how temperature affects their abilities. You might believe it or not, but I did so long ago. Hence my opinion.

Perhaps YOU might want to consult the merck index, search for "solubility of methylamine gas" with google, check some MSDS for methylamine(g) - simply inform YOURself about the fact that all gases dissolve to a less extent in liquids when these have high temperatures.

In case you don't have any possibility for checking it yourself, here's a screenshot:



Maybe the reason why you didn't succeed with cold methanol was the high gas temperature. Why would you need kilos of methylamine freebase BTW? One kilo equals 32.19 mol methylamine, good enough for over 2 kilos of P2P for example. Are you sure you need that much? (why are you asking in the newbee forum then?  ;) )

Suggestion: take a small portion of your gassed MeAm solution, weigth it. Now quickly heat it to a boil, and quickly cool again. Then weigh your solution again, and you'll see that it has become lighter/less dense. Because the gas has left its solvent.

LaBTop used cooled MeOH too, BTW.

lugh

  • Guest
Applicable Papers
« Reply #10 on: September 28, 2004, 06:29:00 PM »
Most of the questions concerning CH3NH2 posed in

Post 529119

(Bandil: "Preparation of anhydrous MeNH2 / HCl etc.", Newbee Forum)
can be answered by finding and reading:

Z physik Chem 128 399 (1927)
J Phys Chem 25 160, 204, 605 & 721 (1921)
J Phys Chem 26 256 & 349 (1922)

These citations can bee found in the file from

Post 480133 (missing)

(lugh: "Happy New Year", Newbee Forum)
 ;)


pooky

  • Guest
Like P said..
« Reply #11 on: September 30, 2004, 04:41:00 AM »
Try it,it will be 55C- give or take.Dare you ;)
Simple fact is,it works.

The stuff was not made to sit in the freezer....and BTW P pops in to the NewBee forum to help people.And you?
Toddle loo from Hong Kong!!:)


indole_amine

  • Guest
give or take - how do you mean this??
« Reply #12 on: September 30, 2004, 06:34:00 AM »
If you really nead kilos of methylamine freebase dissolved in methanol, you should prepare to wait LOOOONG time for the gassing to finish...
(but I don't believe you anyway)

And if I ever attempt gassing methylamine, I won't heat the solvent to its boiling point - promised... :P

(maybe you smartass should begin to think a bit: why does gassed methylamine stink? why does ammonia do? Yes - they leave their solvent, i.e. gas out. And why do they do? Because the solvent is above their boiling point. What could you do against it? Umm, let's see.... maybe COOL IT?)

But as it seems to work for you: go ahead and gas into hot methanol... :(


indole_amine

r2e3

  • Guest
points taken
« Reply #13 on: October 01, 2004, 01:04:00 AM »
i will try the hot version, as i have only really done the cool one (-20->5C). yields were ok. i did end up using alot(!) of MeNH2.HCl and i find making it hard work... (concentrating mother liquor sucks and recrystalisation is equally as time consuming...)

I will let you know comparative % yields etc. This will take approx a month as I am in the midst of sorting precursors out. 

Another concern at this point in time is H20 in the MeOH.
(and yes cold verses hot gassing will make a big difference. i have seen condensation on the inside of my flask and been thinking all the time - shit - water in the reaction mixture. (so add more silica later...)

I dry the MeOH with silica gel first for a few days to soak up the existing trace water, then strain the pellets out
(I realise cooling or heating at this point is optional)
and then gas.

I add a concentrated MeNH2.HCl solution to pellets of NaOH. The gas evolved is then dried over NaOH pellets. In theory it should be anyhydrous.

Now I place silica gel into the reaction mixture to mop up H2O formed during addition of NaBH4 to maximise yield.
In the literature it says that the reaction mixture should be allowed to stir for 1-2 days or there abouts but the silica gel makes stiring of any kind difficult. The stirrer bar just gets caught up and results in generally inefficient stirring... :(

A solution to this would be most welcome.

I guess gram usage in the generation of 10%MeOH is what this is all about. I will quantify.

Just have to dry the damned chloroform off without introducing water... can feel a UTFSE session coming on... (or just shoving it in a flask and sticking a vacuum on it :) )

Anyhow, any points of view are welcome.

Want to achieve the 90%+ efficiency mark 8)

Organikum

  • Guest
Uhuuu.... Gassing methylamine into alcohol is...
« Reply #14 on: October 02, 2004, 02:51:00 PM »
Uhuuu....

Gassing methylamine into alcohol is done staged up of course.
one - two - three, this are the lined up receiving vessels. Bubble into one, outlet over one bubbles into two and so on.
Over times you will end up with high-concentrated MeAm in number one and the concentration gets lesser in two and even more less in three.
Also you will have a little overpressure in number one what helps too.

Store number two and three for the next run. Then number two gets number one, number three number two and number three is a fresh one.


btw. MeAm has a boiling point of -6°C.


r2e3

  • Guest
thanks organikum
« Reply #15 on: October 02, 2004, 10:38:00 PM »