starlight_
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Magnesium methoxide in dmso
Magnesium methoxide can be prepared as a gel-like sludge by reacting activated magnesium metal with dry methanol.
If the target is Mg(OCH3)2 in DMSO, is it reasonable to add DMSO to the sludge and distill off the methanol under inert atmosphere?
Or is it better to heat the sludge to dryness under inert atmosphere and then try to dissolve the hard cake of Mg(OCH3)2 in DMSO (in the same vessel)?
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walruslover69
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Add the DMSO and distill off the methanol probably, are you sure the alkoxide is soluble in DMSO?
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clearly_not_atara
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Could you just add some MeOH to DMSO followed by an excess of Mg, then remove any metal that doesn't react? I don't recall a rule saying that MeOH has
to be neat to react with Mg.
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starlight_
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Quote: Originally posted by clearly_not_atara | Could you just add some MeOH to DMSO followed by an excess of Mg, then remove any metal that doesn't react? I don't recall a rule saying that MeOH has
to be neat to react with Mg. |
This is a great idea and is worthy of a test.
I have not tested the solubility, but am led to believe it is.
Thank you both for your thoughts and advice.
[Edited on 3-12-2018 by starlight_]
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unionised
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Beware the reduction of dmso to dimethyl sulphide.
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starlight_
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Good point. Will that happen as a result of the activated metal reacting in the DMSO?
[Edited on 3-12-2018 by starlight_]
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clearly_not_atara
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yeah that would suck. My instinct says it's pretty unlikely -- sulfoxides are reduced only with difficulty, unless O is electrophilically attacked --
but it's obviously a problem if it happens.
All of the examples here use some kind of electrophile or Lewis acid to activate the sulfoxide so it can be reduced:
https://www.organic-chemistry.org/synthesis/S1H/reductionssu...
but in order for an exhaustive search I think we would need someone who has access to Reaxys.
[Edited on 3-12-2018 by clearly_not_atara]
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Tsjerk
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I think the possible dimethyl sulfide problem can be avoided by reacting the magnesium with methanol before adding the DMSO. Methanol should be easy
to pull of after that.
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walruslover69
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Just out of curiosity
1) how dry does the reaction need to be for methoxide production? If it has to be extremely dry I would recommend adding the DMSO after you make the
methoxide because of it being hygroscopic. But my intuition says it isn't that sensitive to moisture.
2) watcha makin?
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Safety_Lucas
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I actually just got done making a batch of magnesium methoxide by refluxing magnesium in methanol. It didn't work as I anticipated though because very
little or perhaps none of the magnesium methoxide dissolved in the methanol. A paper I was reading suggested that it was quite soluble and it is sold
commercially at up to 10% solutions by mass in methanol. The amount of magnesium I added should have been enough for an 8% solution but much of it was
undissolved. Also starlight, from what I've read, the formation of a gel only happens if water is present in the solution. The methoxide hydrolyzes to
form a lattice of magnesium hydroxide nanocrystals, which behaves as a gel. And in my experiment just a few moments ago, I did not get a gel, just a
milky white precipitate in methanol. Although I did not use any other solvent as you are wanting to do.
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starlight_
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So, some results.
Magnesium methoxide was prepared from activated magnesium and anhydrous methanol in dry glassware under inert gas.
The mixture became solid on cooling, and DMSO was added.
Methanol was distilled off under light vacuum at around 50C (this took ages). There was one tiny (~2mm) magnesium turning left in the reaction flask
during this process.
The result was a powerful and unholy stink of DimethylSulfide that filled the whole lab, and still persists to some extent two days later.
I would advise against doing this the same way as the smell is just too bad. Perhaps it was the tiny amount of magnesium carried over leading to
reduction of the DMSO. If so, don’t even think about making themagnesium methoxide in the DMSO solution! Unionised, your warning was prescient!
[Edited on 9-12-2018 by starlight_]
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morganbw
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Thank you, sir, info received.
Other magnesium salts?
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unionised
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News to me- and to Swern I guess
https://en.wikipedia.org/wiki/Swern_oxidation
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starlight_
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They should be fine I would guess
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clearly_not_atara
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unionised: touche (although, oxalyl chloride isn't mild imho)
starlight: was formaldehyde produced? Could you test for formaldehyde?
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starlight_
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I’m not sure, I hope not
I can’t test anything, as the reaction is now disposed of, and the smell is too bad to run again without a fume hood.
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