Sciencemadness Discussion Board - Magnesium methoxide in dmso


	Not logged in [Login ]

FAQ

Member List

Today's Posts Forum Stats

Stats

Back to:

Sciencemadness Discussion Board » Fundamentals » Organic Chemistry » Magnesium methoxide in dmso

Printable Version

starlight_

Harmless

Posts: 18
Registered: 7-11-2018
Member Is Offline

posted on 3-12-2018 at 10:39

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)?

walruslover69

Hazard to Others

Posts: 216
Registered: 21-12-2017
Member Is Offline

Mood: No Mood

posted on 3-12-2018 at 13:13

Add the DMSO and distill off the methanol probably, are you sure the alkoxide is soluble in DMSO?

clearly_not_atara

International Hazard

Posts: 2692
Registered: 3-11-2013
Member Is Offline

Mood: Big

posted on 3-12-2018 at 13:42

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.

[Edited on 04-20-1969 by clearly_not_atara]

starlight_

Harmless

Posts: 18
Registered: 7-11-2018
Member Is Offline

posted on 3-12-2018 at 14:25

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. :cool:

Quote: Originally posted by walruslover69

Add the DMSO and distill off the methanol probably, are you sure the alkoxide is soluble in DMSO?

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_]

unionised

International Hazard

Posts: 5102
Registered: 1-11-2003
Location: UK
Member Is Offline

Mood: No Mood

posted on 3-12-2018 at 14:30

Beware the reduction of dmso to dimethyl sulphide.

starlight_

Harmless

Posts: 18
Registered: 7-11-2018
Member Is Offline

posted on 3-12-2018 at 14:38

Quote: Originally posted by unionised

Beware the reduction of dmso to dimethyl sulphide.

Good point. Will that happen as a result of the activated metal reacting in the DMSO?

[Edited on 3-12-2018 by starlight_]

clearly_not_atara

International Hazard

Posts: 2692
Registered: 3-11-2013
Member Is Offline

Mood: Big

posted on 3-12-2018 at 14:52

Quote: Originally posted by unionised

Beware the reduction of dmso to dimethyl sulphide.

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]

[Edited on 04-20-1969 by clearly_not_atara]

Tsjerk

International Hazard

Posts: 3022
Registered: 20-4-2005
Location: Netherlands
Member Is Offline

Mood: Mood

posted on 4-12-2018 at 00:15

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.

walruslover69

Hazard to Others

Posts: 216
Registered: 21-12-2017
Member Is Offline

Mood: No Mood

posted on 4-12-2018 at 06:21

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?

Safety_Lucas

Harmless

Posts: 6
Registered: 28-9-2017
Member Is Offline

Mood: Radical

posted on 9-12-2018 at 10:55

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.

starlight_

Harmless

Posts: 18
Registered: 7-11-2018
Member Is Offline

posted on 9-12-2018 at 12:13

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_]