Has anyone here any experience in making their own trimethylamine? I am wondering if the volatility of TMA is so high such that it is necessary to
collect it in a receiving solvent. It seems that way, judging by the way the Org Syn only gives a protocol for TMA hydrochloride and TMA freebase
collected into a solvent.
My question: Is it impractical to procure TMA free base in this manner:
- carry out the reaction (ammonium chloride + p-formaldahyde ---> TMA HCl)
-liberate TMA freebase from crude mixture via dropwise addition of NaOH
-under low heat, TMA travels out of the flask, up through a column, and down through a condenser, and into empty receiving flask.
Perhaps a drying flask should be employed before the receiving flask.
Thoughts?mr.crow - 27-12-2011 at 21:40
The orgsyn websites appears to be broken
Trimethylamine is a gas at room temperature with BP = 2.87 deg
So yeah you need a solvent or pressurized cylinderDr.Bob - 28-12-2011 at 06:25
Since it is a gas, you do have to either trap as a salt or use a very good condenser (dewer type with dry ice/acetone is best) to trap it. It also
stinks something terrible, like a fish that has rotted for days, so you will have your neighbors calling the police about the dead body odor if you
are not careful. The HCl salt is a great form of it, very stable and easy to store. If you just want a base, triethylamine is much better and
easier to deal with. TMA might also react with some drying agents, so I would suggest that if drying it, you be careful what you pick. NaOH might
work OK, but P2O5 would react strongly with it, for example. resveratrol - 28-12-2011 at 12:02
hmmm....this is what I thought, thanks guys. Thanks for the advice Dr.Bob, you're right - I would be better suited with TEA, but I do not know of an
easy route to synthesis, nor acquision nowadays. Do you know of a synth?Dr.Bob - 29-12-2011 at 05:22
Simplest would be excess ethyl iodide and ammonia in a polar solvent with K2CO3. It is hard to stop the alkylation from going completely. Or the
reductive amination of acetaldehyde and ammonia, but that would be much more challenging to find the chemicals. There are bound to be published
routes to TEA via Google Books.Adas - 29-12-2011 at 06:15
Simplest would be excess ethyl iodide and ammonia in a polar solvent with K2CO3. It is hard to stop the alkylation from going completely. Or the
reductive amination of acetaldehyde and ammonia, but that would be much more challenging to find the chemicals. There are bound to be published
routes to TEA via Google Books.
IIRC, reaction of acetaldehyde and ammonia gives acetaldehyde-ammonia trimer. Wikiresveratrol - 29-12-2011 at 07:33
hm....although TEA would be preferable, I think TMA would be an easier synth. I have a graham condenser (with coiled condensate path) that I think
would be useful in this particular instance...in conjunction with the dry ice/acetone bath - I think I could pull it off.peach - 29-12-2011 at 09:21
With a BP of 2-3C, you'll need your condenser to be at -20 or so. Which happens to be the temperature of a salt / powdered ice slushy.
Of coarse, you can't pump water at that temperature through a graham, or the slush it's self, it'd need to be water + antifreeze cooled to that point
- somehow. There are various methods for getting the coolant that cold (store it in the freezer), but by far the easiest is to use a dewar / cold
finger condenser and pour the slush in.
I would go with Dr.Bob and Mr.Crow's absorb or react it to something with a higher BP suggestion. It'll be easier to handle that way as well since,
even if you condense it and store it in the freezer, it'll soon be trying to evaporate / boil away again as soon as it comes out.
Adas - 29-12-2011 at 09:30
Peach, why these complex procedures? The easiest thing is to make HCl salt, and when needed, release it using NaOH + some water. TMA is a gas, so you
can also trap it in a balloon. peach - 29-12-2011 at 09:36
Well it depends how much resveratrol needs and how long he plans to store it for. He seems interested in actually obtaining it as a liquid but I 100%
agree with you, it'd be far easier to produce it when needed and run it directly into the thing it's needed for. resveratrol - 29-12-2011 at 11:35
hiya peach. thanks for chiming in.
I only require small multigram amounts, but the difficulty is the introduction of the tertiary amine.
trapping as a salt would be easiest, as Adas says. But it is indeed the freebase that I'm after. I suppose I could trap as HCl salt, weigh the
correct stoiciometric amounts I would need for my reactions, and liberate with NaOH into receiving reaction vessels. However, it would be difficult
to note what quantities were delivered, and I do not wish to add the hydrochloride salt directly.peach - 29-12-2011 at 15:39
You could set it up to re-generate the free trimethylamine in a second flask, giving it a gentle warm to push it through some tubing to the reaction
it's self and then, once it seems to have to come to a stop, blowing some inert gas in behind it to rinse as much of the stationary gas in the dead
space out and into the reaction it's self. If it's warm enough where you are, you may not even need to bother with that. I only mention it because
it's quite cold where I am and it could actually get cold enough in some places for it to stay stuck in the generator. You can estimate the quantity
that will remain behind in the water Adas mentioned by checking it's solubility in that at the temperature your generator is running.
You should also consider Mr. Crow's suggestion further.
Quote:
Occupational Safety and Health Guideline for Trimethylamine
Solubility: Very soluble in water; soluble in ether, alcohol, benzene, toluene, xylene, ethylbenzene, and chloroform.
Generate it and bubble it into whichever best suits your needs. You can then titrate the resulting solution to find it's concentration, and then use
the concentration to dose a measured aliquot into the reaction it's self.
Mr Crow's suggestion, despite the need to titrate the solution if you want an accurate measure, will likely be the easiest and most accurate.
You could also cheat the titration stage by instead cooling the solvent well, saturating it and then allowing it to come up to the temperature you
require with Adas' balloon on the bottle. You should end up with a predictable concentration then based on the solvating capacity of
whatever you've chosen to bubble it into. You will want to cool it well below the temperature you'll be using it at, as it can be difficult to get
liquids fully saturated at the temperature they'll be used at (the absorption rate drops off entirely as they approach the saturation point).
[Edited on 29-12-2011 by peach]resveratrol - 29-12-2011 at 18:00
Thank you for all of the suggestions. This is what seems easiest to me:
1) trap as the hydrochloride salt
2) liberate TMA with NaOH and trap in a balloon (calculate the quantity of TMA needed and use a 50-100% excess of the salt for this step)
3) put balloon(s) in freezer until TMA is needed for reaction
4) pour the TMA from balloon into empty beaker, place on tared scale until TMA evaporates to correct stoiciometric amount
5) pour into reaction vessel
All is well until the TMA eats through the balloon lol (not sure if this would happen). The balloon was a great suggestion, although is it something
suitable for long-term storage of tertiary amines? I wouldn't expect liquid TMA to dissolve anything contained in a balloon, but you never know.
Peach, you had me wondering what the solubility of TMA would be in DCM. peach - 29-12-2011 at 18:37
Peach, you had me wondering what the solubility of TMA would be in DCM.
Searching google with: trimethylamine "methylene chloride"
The second result's cache read:
Quote:
over 2 hr into a stirred solution of triethylamine. (80.8 g, 0.8 mol) in methylene chloride (150 ml) in an ice bath
Changing the search string to: trimethylamine dichloromethane
The top result is:
Quote:
The chloromethylation of triethylamine in dichloromethane.
Also try: trimethylamine DCM
There are many results all mentioning trimethylamine and DCM under one of those names, which will contain details of DCM solution concentrations.
I would not at all enjoy the idea of storing anything for any prolonged period inside a balloon. They struggle to contain air, let alone reagents.resveratrol - 29-12-2011 at 20:02
I'm surprised you didn't send me a lmgtfy.com link lol. Thanks, I'll look into that further.
Another question I'd like to have answered, if someone would be so kind. Can one expect reasonable purity when using OTC sources of paraformaldehyde?
It seems this dirty "Campa Chem" is the most widely used, where some are reportedly doing methanol washes of the ground substance to clean it. Given
the intended use of this product, and the undoubted presence of volatile fragrances and perfumes, I am a little bit apprehensive to use it as a
precursor to TMA. Is this feeling warranted, or am I just nit-picking?
[Edited on 30-12-2011 by resveratrol]Nicodem - 30-12-2011 at 15:06
I don't understand why would you want to form trimethylamine gas from its hydrochloride if all you need is its solution in an organic solvent, but
just for your information: trimethylamine reacts with dichloromethane to considerable conversion in matter of hours.
PS: The use of such a grim acronym as TMA for something that can be shorthanded as Me<sub>3</sub>N (if really needed), makes me wander if
people always use acronyms just to annoy other people? I admit that I sometimes do.resveratrol - 30-12-2011 at 17:40
Nicodem, it DOES get annoying when people use misleading/thought-up acronyms, but in this case I felt everyone would know what TMA stood for. Not to
mention my keyboard does not have subscript functionality. It's really too bad I decided to type three sentences explaining why I essentially didn't
want to waste the time to convey something correctly the first time around...tsk tsk
In regards to your question, formation of the salt seemed like the best option (long term storage). I agree it is a bit redundant to then collect as
a gas when its eventual fate is likely to be dissolved in DCM (for use as a proton scavenger), but it allows me to be more sure about what's going
into the reaction. Admittedly, I'm sure I could just generate directly to the reactions and not worry about there being an excess of the amine, but
whatever. Do you have a better suggestion, Nicodem?
Thanks Bot0nist - 30-12-2011 at 17:43
Quote:
Not to mention my keyboard does not have subscript functionality.
