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Sauron
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[*] posted on 15-9-2007 at 20:58
Methylamine Purification


One of the hassles in preparing methylamine hydrochloride and/or methylamine base is seperating it from the significant amount of ammonium chloride or NH3 always present in the mix resulting from the reaction of ammonium chloride and formaldehyde.

As we have seen in the Anhydrous Ammonis from Urea thread, NH3 forms solutions with some salts, notably CaCl2, corresponding to hydrates. These are solids (in some instances) with definite ratios of NH3 to salt such as CaCl2.4NH3 and CaCl2.8NH3 and these are designated as ammines or ammoniates.

I am wondering whether methylamine behaves similarly?
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[*] posted on 15-9-2007 at 21:36


Yes, don't have details but see http://www.sjtuirc.sjtu.edu.cn/news/061212%20A%20consolidate...

Also most lab technique books say that CaCl2 should not used for alcohols, phenols or amines because of the formation addition compounds.



[Edited on 16-9-2007 by not_important]
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Sauron
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[*] posted on 15-9-2007 at 22:24


In that case, then, CaCl2 and maybe some of the other salts that adsorb NH3, may also be useful for temporary storage of anhydrous MeNH2.

In the case of NH3, some ammonium salts form liquid salt-ammonia solutions that can be stored between ambient and lower temperatures and have relatively low, certainly sub-atmospheric vapor pressures, but nevertheless will release NH3 when moderately heated (say on a water bath) at a reasonable rate. Ammonium thiocyanate alone or admixed with ammonium nitrate is or was used for adsorption of NH3 from process streams in ammonia synthesis. Ammonium thiocyanate is particularly rapid is ints deliquescence in an ammonia atmosphere while ammonium nitrate is slower but stores more NH3.

CaCl2 adsorbs ammonia much more sluggishly but has great capacity (up to 8 mols NH3 per mol CaCl2) and is still solid, though it swells in volume about 4X, and on mild heating releases 6 of those 8 ammonia molecules. This is basis of adsorbant refrigeration systems using solar heating which are in commercial use today.

I was rather hoping that an adsorbant could be found that would discriminate between NH3 and MeNH2. But maybe it won't be one of this sort. Perhaps a zeolite is more likely, analogous to that used for drying ethanol.
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[*] posted on 15-9-2007 at 22:31


3a sieves should selectively adsorb NH3, but not MeNH2.
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[*] posted on 15-9-2007 at 22:34


When I made methylamines ammonium chloride and formaldehyde., intentionally shooting for an average of the diamine, I just used extraction of the dry hydrochlorides by dry isopropanol to pull out the methyamines. When I used the methanol-ammonia-hot tube route I did it in winter and fractional distillate to remove ammonia from the amines. The roughly 30 C difference in boiling points made the distillation not too challenging.
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[*] posted on 15-9-2007 at 23:03


Thanks. Yes 3A was my best guess, I was about to look up the details.

And I will have to review the methanol/NH3 hot tube method.

Dimethylamine is on my to-do list as well.
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[*] posted on 15-9-2007 at 23:31


The hot tube route gives a mixture of all three methylamines, see US6166258 and Zeolites Volume: 18, Issue: 5-6 May 6, 1997, among others. You can boost one amine by controlling the ratios of ammonia to methanol, and recycle unwanted amines to increase the yield of wanted ones.

I used a preliminary fractionation to get mixtures of the primary and tertiary amines, and secondary and tertiary amines. After that it was solution in different solvents to separate the hydrochlorides, and differences in pKb.
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[*] posted on 16-9-2007 at 08:33


The hot tube method gives lots of trimethylamine even when a molar excess of ammonia is used.
And how are you going to fractionate that, with all boiling points being well below room temperature? A column doesnt work under such conditions, except if you fractionate under pressure or the ambient temperature is below the boiling point of the amines.

Is methylamine unavailable in Thailand as well?
I got 1L of 40% methylamine solution, which I ordered recently, standing in my room at the moment (I'm going to make nitrosomethylurea from it). In germany it is no problem to buy it, there are good internet suppliers...

Gattermann uses an extraction of the crude dried hydrochloride mixture with chloroform to remove di- and trimethylamine*HCl and then an extraction with absolute ethanol which only dissolves methylamine*HCl to get rid of the last NH4Cl.

I found that the recrystallization of methylamine-HCl from 99,5% isopropanol is very good as well for separating it from ammonium chloride: when pure MeAm-HCl was boiled with IPA, the hot solution decanted and left to cool it deposited crystals.
When the same procedure was repeated with pure ammonium chloride, no crystals appeared upon cooling.
So there is no need to use precious absolute ethanol.

Though the solubility of MeAm-HCl in IPA wasnt exactly great even at the boiling point- a soxhlet extraction would be preferrable to avoid having to use large amounts of IPA.

[Edited on 9-10-2007 by garage chemist]




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[*] posted on 16-9-2007 at 16:34


I have not tried to buy methylamine here as yet. It is not a priority, I was just triggered into thinking about it by the thread on metal salt solutions on NH3 with a tangent off to zeolite seperation of NH3 from MeNH2.

I think I can buy 40% aq MeNH2 easily enough and maybe the neat liquid under vapor in cylinder. Not so sanguine about Me2NH in any form as it is on the Thai MOD restricted list. Some things on that list they are lax about and I can buy as long as qty is not large. But it's unpredictable.
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[*] posted on 16-9-2007 at 19:52


Dimethylamine is most easily made in the lab by hydrolysis of DMF, either with HCl (distill off formic acid, HCl and water to leave Me2NH*HCl behind) or with NaOH solution to give gaseous dimethylamine.
I think you can buy DMF easily, I can't due to it being classified as toxic in the EU. But I have 500ml at home which will be plenty for my uses.




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[*] posted on 16-9-2007 at 20:20


Quote:
Originally posted by garage chemist
The hot tube method gives lots of trimethylamine even when a molar excess of methanol is used.
And how are you going to fractionate that, with all boiling points being well below room temperature? A column doesnt work under such conditions, except if you fractionate under pressure or the ambient temperature is below the boiling point of the amines.


You need to use a large - many moles - excess of ammonia if the monoamine is the target. And yes even then you get some triamine, which as I said can be run back through the tube with the NH3+MeOH; depending on who you read this either recycles the triamine which hands methyls off to ammonia, or simple suppresses the formation of additional triamine.

And I did say that I used fractionation during the winter. A temperature of -10 to -15 C works well for condensing the amines and stripping ammonia out of them. Fractionating to separate the amines really is only good for splitting the mono and di amines, the triamine ends up in both with the columns I have.
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[*] posted on 16-9-2007 at 20:27


Thanks, Yes, DMF is easy to come by. I was not familiar with that very handy conversion.

I have at least a 2,5 L jug of SMF on hand.
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[*] posted on 16-9-2007 at 21:00


Whoops, I meant "..even when a molar excess of ammonia is used". Typo.

That is surely a preparation best done in winter, yes.
How did you heat the tube? What did you use as catalyst / how did you make the catalyst?
That tube apparatus for methyl- and ethylamines would surely be very interesting for us all to see documented in Prepublication, dont you think?

Sauron, make sure all DMF gets converted when using HCl, amides arent that quickly hydrolysed. Reflux for several hours with excess of HCl.
The NaOH method would be better since you can see how fast the hydrolysis is going due to the dimethylamine being liberated as gas.




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[*] posted on 16-9-2007 at 21:16


Dimethylamine base isn't hard to condense. bp 7 C d 0.68 Also it's nicely soluble in water, usual commercial solution is 33%. so you can collect it in a dewar or directly into a lecture bottle or dissolve it in water.

This hydrolysis should have been obvious to me, but I am so accustomed to thinking of DMF as a solvent, ar as a reagent, that I overlooked this potential. Shame on me.

[Edited on 17-9-2007 by Sauron]
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[*] posted on 16-9-2007 at 21:37


Now that I think of it, dont use HCl, it would catalyze the decomposition of the formic acid into carbon monoxide, especially when heated. That would be really bad if one did this outside of the fume hood and then thought "hey, whats that fizzing, that reaction wasnt supposed to produce any gas..."



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[*] posted on 19-9-2007 at 07:41


Quote:
Originally posted by not_important
The hot tube route gives a mixture of all three methylamines, see US6166258 and Zeolites Volume: 18, Issue: 5-6 May 6, 1997, among others. You can boost one amine by controlling the ratios of ammonia to methanol, and recycle unwanted amines to increase the yield of wanted ones.

I used a preliminary fractionation to get mixtures of the primary and tertiary amines, and secondary and tertiary amines. After that it was solution in different solvents to separate the hydrochlorides, and differences in pKb.


US2085785 has a procedure for making alkylamines by heating ferric chloride with ammonium chloride and the desired alcohol in a pipe. "Uncle Fester" cites it in his nefarious "Advanced Techniques" book, but I've never heard of anyone trying it, whether for disreputable purposes or not.

The secondary and tertiary amines are separated out by dissolving and recrystallizing the amine-slurry in 190 proof alcohol.
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[*] posted on 19-9-2007 at 12:12
an odd thing happened


I was running the first reduced pressure distillation of formaldehyde/NH4Cl reaction mixture.

System: flask->filter/vacuum regulator/filter flask containing KOH flakes->trap(acetone/dry ice)->pump

I got the flask going a bit too vigorously and ran some liquid into the filter flask. I stopped everything to clean the filter flask and replace the KOH flakes. The reaction between the contaminated KOH and water was 'intense man' as they say. Vey vigorous-more so than solvation of KOH by water would explain. I was appreciative of my gear! What happened? I speculated that some K got reduced by formate in the liquid and subsequent exposure to water released H2 and heat.

This seems a little round the bend and have one other plausible (?) scenario. I'm thinking the mixture has methylal, methlyamine, formaldehyde, methyl formate, formic acid (?) and maybe the last is neutralized by aqueous KOH with much drama. Would like to hear from anyone as to what really happened there.

Thanks,
CRX
(seems like reagent replentishment time for a few of us)

[Edited on 19-9-2007 by chemrox]
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[*] posted on 20-9-2007 at 01:54


IMHO several fractional crystallisations (the ammoniumchloride comes out first) and then extraction with dry IPA or prferably butylalcohol is the standard.
An old textbook states though that even with EtOH 96% a purity of 98% is achieved which is sufficient for most purposes.




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[*] posted on 20-9-2007 at 08:27


Quote:
Originally posted by chemrox
I was running the first reduced pressure distillation of formaldehyde/NH4Cl reaction mixture.

System: flask->filter/vacuum regulator/filter flask containing KOH flakes->trap(acetone/dry ice)->pump

.... I'm thinking the mixture has methylal, methlyamine, formaldehyde, methyl formate, formic acid (?) ...


Formic acid is a fairly strong acid, unlikely to have it and an amine free at the same time. If you were distilling the raw NH4Cl/CH2O mix then the amines are tied up as HCl salts, if it had been neutralised with base then the acids would be salts, and methyl formate may have hydrolyzed to some extent to MeOH and formate salt.

I don't see why you're vacuum distilling this mixture, none of the products have boiling points over 42 C at one atmosphere. Given that the vapour pressure of the monoamine is greater than 10 mmHg at the temperature of the dry ice trap, a decent vacuum is going to suck the amine right out of the system, including out of the cold trap.
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[*] posted on 8-10-2007 at 11:50


CRX and I were talking about this and concluded the Vogel procedure is right and the Rhodium version of it is wrong. @not_important : vacuum sucked the amine right out. We are going to have to run the synthesis again without resorting to vacuum and using better T control. I'm not a chemist and CRX says he's out of practice and has a lot to catch up on. But I can read a thermometer and turn the control on a rheostat or yell for help.
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[*] posted on 8-10-2007 at 12:21


Vogel probably pirated the procedure from Org.Syn., anyway, all he usually did was reduce the scale.

I'd go look at the Org.Syn. entry on MeNH2 and pay attention to the notes, discussion, and references to the primary literature.




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[*] posted on 8-10-2007 at 16:23


Notice the use of chloroform in the purification of the HCl salts. Alternatively, column chromatography can be used to separate HCl and freebase amines. Column chromatography with molecular sieves as the stationary phase with freebase amines in solution.

TRIMETHYLAMINE HYDROCHLORIDE http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0531

METHYLAMINE HYDROCHLORIDE http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0347

[Edited on 9-10-2007 by WizardX]




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[*] posted on 8-10-2007 at 16:50


I see we're indeed using reduced pressure...

CHCl3 gets the dimethylamine out ..as I understand it ... not sure about the alcohol

Looks like Vogels re-published Org Syn for 1kg instead of 4kg NH4Cl and I missed the reduced pressure part when I read it there. I should be using a water pump not my vacuum pump but I need to do major re-plumbing and haven't found the time.

[Edited on 8-10-2007 by chemrox]
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[*] posted on 9-10-2007 at 06:05


I would say that isopropanol is preferred solvent these days for separating out the NH4Cl. At the time of the OS procedures ethanol and n-butanol were produced by fermentation on a industrial scale, IPA was a specialty chemical often made from acetone, which in turn was a product of making wood alcohol by destructive distillation. As garage chemist demonstrated, the solubility of NH4Cl in dry IPA is quite low, you can do a hot extraction, allow the amine hydrochlorides to crystalise out, and reuse the solvent for a second extraction of the ammonium chloride to get the last of the amines.

The use of a reasonably non-polar solvent still seems to be the simplest way to separate the mono from the di and tri amine hydrochlorides. Unfortunately I've never seen solubility figures for the thre salts in such solvents, except for 16,8 g of Me2NH2Cl in CHCL3 at 25 C.

The free amine base strengths might give a way to separate them. going from NH3 to NMe3 the pKa values are 9,25 10,64 10,73 9,8
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[*] posted on 14-10-2007 at 00:17


do you think drug store 99% IPA is sufficiently dry or should we purify it? I assume it makes an alkoxide with Na and wonder if it can be dried enough with CaCl2 or should we sacrifice some Mg turnings or distill it from slake lime?

@Sauron why do you think DMA isrestricted where you are? I'm trying to think of a drug that's made with it and am coming up short except for DMT and that hardly seems a cause for outlawing a useful reagent.
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