Furboffle
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help preparing aqueous 40% dimethylamine solution
I need to prepare a 40% solution of dimethylamine. Im trying to trying to make an amide from an ethyl ester. I have the dimethylamine hydroiodide salt
to work with. I'm curious how this works compared to regular 40% aqueous solution available from suppliers. Is the fact that its a salt an issue? I'm
worried that by preparing a 40% solution the hydroidide portion will acidify the water and in turn hydrolyze my ester upon addition. Is this a
legitimate concern?
I've been trying to think of a way to get the freebase amine in solution but due to it being a gas it seems a little more tasking with using water and
removing the iodide ions.... so I've debated using a NaOH methanol solution to basify the amine and salt out NaI which would be easy but that's hoping
the amine salt is soluble in basic methanol since I expect it has little to no solubility in regular MeOH...
Would this basification step be necessary or would the aqueous dimethylamine hydroiodide work satisfactorily without tampering with the solution
preparation?
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Furboffle
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I feel like if the methanol route could work it might allow me to perform a reflux with much less concern of hydrolysis from an aqueous solution..
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Scr0t
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NaI is quite soluble in Methanol also neutralizing the Hydroiodide salt will generate water.
One way is to set up a flask containing an aqueous solution of Dimethylamine Hydroiodide with a condenser and a dropping funnel containing an
equimolar amount of NaOH solution. Add the NaOH, heat and reflux the solution.
Dimethylamine gas should pass out the top of the condenser which can be piped through a trap containing solid NaOH (to dry it) then pass it into a
stirred and cooled beaker of Methanol using an inverted funnel to prevent suck back.
It's the same setup one would use to prepare methanolic Ammonia and Methylamine solutions.
You can skip the dropping funnel if the NaOH solution is cool before you add it and there's sufficient water present overall.
You could improvise something more like this if you have limited glassware.
https://www.sciencemadness.org/talk/viewthread.php?tid=16061
Of course you would definitely want to boil down the remaining aqueous solution to recover the NaI.
You could of use Dimethylformamide/NaOH hydrolysis to generate the Dimethylamine instead.
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Furboffle
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for this I was expecting it but 1) it would be far less water generated than straight up dissolving in water and 2) I planned on using magnesium
sulfate or calcium chloride to dry the methanol. but if ultimately NaI is soluble then it doesn't help...
though I would rather have sodium iodide present than acid...
I don't have a trap so something like the thread you posted would have to do, but I have enough glassware to device something slightly less
improvised. perhaps just run a hose from the top of the condensor to a stoppered filtration flask.(you think there would be too much of an issue of
pressure build up? or perhaps use that to my advantage to force the gas into solution...
I don't particularly want to go that route right away but if it comes to it then so be it. are there other salt/precipitate routes that come to mind
in regard to methanol that could work synonymously with the NaOH->NaI idea I was hoping for?
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Scr0t
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Calcium chloride is not compatible with alcohols or amines so it's best to avoid that one.
For a trap you could use a Dreschel head and bottle or improvise one from a jar with a metal screw lid and two lengths of copper tube soldered into
it. Or maybe a modified inline filter for water or petrol.
I can't comment too much about pressure build up without seeing the apparatus but you need to make sure that the gas passes through the desiccant
rather just pass over it as drying efficiency would be low.
Don't try to use pressure to get it to dissolve as something may pop-out and break, just bubble it through the Methanol.
The surest way is to prepare a pure solution, whether some metal salts or some water present is going detrimentally affect yields I don't know.
But you can experiment on a very small scale and see for yourself.
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