Sciencemadness Discussion Board

Substitution of Magnesium Methoxide for Sodium Methoxide

Spock - 31-7-2019 at 12:15

I'm planning to attempt to make 2-Nitrobenzaldehyde following this procedure. The only issue I have is the sodium methoxide, as I don't have easy access to sodium metal. I do have an abundance of magnesium however so I'm looking at potentially using magnesium methoxide instead.
Is there something obvious I am missing that would make this unworkable? The methanol has to be distilled off anyway so I can get around the lower concentration solution that I would need to make to avoid the gel consistency that can happen with magnesium methoxoide.

Pumukli - 31-7-2019 at 12:28

My attempt to substitute NaOMe with Mg(OMe)2 in a condensation reaction became a failure. Your planned reaction is different, so don't let my failure discurage you. Negative results are still results and can contribute to the knowledgebase. :)

AvBaeyer - 31-7-2019 at 19:33

In general, magnesium methoxide is not a useful replacement for alkali metal methoxides. When the magnesium compound works, yields typically are much poorer than with eg sodium methoxide. However, in some reactions involving chelation control, the magnesium base may be superior.

I also reviewed the reference you gave. It really looks like a slog and method of last resort for making o-nitrobenzaldehyde in poor yield given the effort required. I recently purchased o-nitrobenzaldehyde on Amazon. That was a lot easier than trying to make it using an OrgSyn prep.

On the other hand, chemistry is an experimental science so perhaps you should try the prep you referenced using magnesium methoxide if you can duplicate the temperature requirements. I would strongly suggest using t-butyl nitrite in place of the much less stable isopropyl nitrite however.


Spock - 1-8-2019 at 15:52

Well, looks like I'll have to make some sodium after all. If I can get it to work with sodium methoxide then I'll try again with magnesium.

The goal of my project is to make indigo using as close to totally over the counter materials as possible. That's what I like about the synthesis I referenced, right now the only things that I have had to order online have been magnesium, sodium nitrite and menthol for sodium production.

The isopropyl nitrite is attractive to me for two reasons, isopropanol is readily available at very good purity unlike t-butanol and it's low boiling point helps with temperature regulation of the reaction.

artemov - 1-8-2019 at 22:26

Not sure if this is useful, nurdrage used sodium hydroxide and molecular sieves to make sodium methoxide.
(read the comments too!)

The yield of his intended product was only 20%, so he went back to sodium, but the yield only increased nominally to 33%

So he concluded that perhaps he should just used more molecular sieves in the first method instead of using the expensive sodium metal.