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digga
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[*] posted on 15-2-2021 at 16:16
Drying methanol


Having decided to do a Fisher Esterification making dimethyl oxalate, I found myself in need of some anhydrous methanol. (water is a product of these reactions, and it's presence can maximize reaction times and minimize yields) I got a 4 pack of Heet gas additive and followed the procedure outlined by Nurdrage:

https://www.youtube.com/watch?v=NMfs3e9OdZQ

I shaved off some Magnesium from a fire starter, tossed it into 250 ml of Heet and got a nearly immediate reaction at an ambient temp of about 60 F. I set it aside for a week as I had to shift some household goods down to Dixie. When I returned I dumped several grams of commercial Mg turnings into about 750 ml of Heet. Nothing happened. The next day I took a digger off the moving truck ramp and broke several bones.

After 10 days, I was well enough to go back in the shed. The Heet/Mg was unchanged. I distilled off the first batch and set it over 3a sieves. The ambient temperature was in the low 40s. I popped 250 or so ml of the Heet/Mg into a refluxing rig. Then I set it to stir and applied just a little heat. Within a few minutes I got steady evolution of gas. It's sitting in the shed on the stir with a Liebig condenser and Vigreux column catching any runaway vapor.

You would think that a product claiming to dry gas would be itself dry. You would be wrong.




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[*] posted on 16-2-2021 at 04:49


Personally I would be satisfied by concentrating such methanol by distillation, I wouldn't require totally water-free methanol. A lot of H2O will be produced during esterification (18 g H2O from 32 g of reacted methanol). Focus on dehydratation of oxalic acid too (usually sold as dihydrate). You can achieve good yield when using Dean-Stark trap apparatus during esterification and something like hexane or medicinal petrolether (redistilled petrolether, using fraction boiling at 60-70 C) as a dehydrating agent.



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[*] posted on 16-2-2021 at 05:09


Digga,
Do you realise that Mg reacts with methanol?
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[*] posted on 16-2-2021 at 11:32


Yes, it produces some Magnesium Methoxide which hydrolyzes to the insoluble and gelatinous hydroxide and methanol.

Mg + 2 Ch3OH = Mg(OCH3)2 + H2

Mg(OCH3)2 +2 H2O = Mg(OH)2 + 2 Ch3OH

That binds the water.


I thought of refluxing through a column packed with 3a sieves. But I do have a Dean Stark in house:)

[Edited on 16-2-2021 by digga]
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[*] posted on 17-2-2021 at 05:07


When you have Dean-Stark trap apparatus then keep your 3A molecular sieves for something where there are unexpendable. Add hexane/isohexanes (I use medicinal petrolether boiling in range 60-70 C, it is produced as hydrogenated fraction in my country) into the esterification reaction and distill out water from the reaction mixture. I have such experience that using 5 ml of H2SO4 is too much and 0,5 ml is enough for 1 mol of ester. Using Dean-Stark you even do not have to use conc. H2SO4 and using battery concentration 37% H2SO4 is fine. Also use the same method to remove water from oxalic acid dihydrate although I guess here you have to use maybe toluene or petrolether with boiling point above 100 C - only guessing, I did not yet perform drying oxalic acid dihydrate (drying by heating - you must keep T very precisely otherwise a lot of it would sublime).



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[*] posted on 17-2-2021 at 09:09


Oxalic acid can be dehydrated directly by heating at 100-110°C.



If you are interested in aqueous inorganic chemistry look at https://colourchem.wordpress.com/main-page/

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[*] posted on 20-2-2021 at 17:18


I used the OrgSyn procedure for making Dimethyl Oxalate, which involved mixing dehydrated Oxalic Acid with Methanol and a Sulfuric Acid catalyst. It happens fast with the product crashing out on cooling. I have filtered it off and am processing the filtrate in my freezer to get more. It is a solid at room temp. It appears that it is very soluble in hot Methanol. Cold Methanol, not so much. Will recrystallize and report on final yield.
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[*] posted on 14-4-2021 at 04:14


Does anyone have any info on how dry fuel methanol is? I couldn't find any product data, but I presume that water content would desirably be low for fuel. Racing fuel methanol is stated to be 99.85% pure, and this is fuel methanol, but without any specification.

[Edited on 14-4-2021 by Fyndium]
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[*] posted on 15-4-2021 at 05:56


K2CO3 is your friend. It is so soluble in water (1.1kg per kg of water!) that it can layer out aqueous MeOH. It's also cheap.

After collecting the alcohol layer, shake over 3A and distill and it will be very dry. Keep in mind that depending on how much carbonate you add and how much water is present, you may not see a real layer - you'll just see the granules of K2CO3 get kind of clumpy and pasty.
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[*] posted on 15-4-2021 at 09:08


K2CO3.. Might need to add some on my next chem supplier order, then. However much I've looked, it's just not sold anywhere at here. And I know where to look.

Meanwhile, I found an alternative synthesis that doesn't call for (anhydrous methanol), being a bit more complex. Water doesn't affect it otherwise, but it causes the insoluble stuff to dissolve, ruining the whole concept.

I suppose one does not simply salt out MeOH with NaOH like IPA can be done?

Gotta UTFSE, but meanwhile, what'd be methods to determine if my MeOH contains significant water?
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[*] posted on 15-4-2021 at 09:53


Quote: Originally posted by Fyndium  
K

Gotta UTFSE, but meanwhile, what'd be methods to determine if my MeOH contains significant water?


Define "significant".
As has been pointed out, each 32 g of methanol which reacts is going to produce 18 grams of water.
So, if it starts off with, for example, 1.8g in 32 g - about 5.5% the amount of water present will be small compared to how much is produced by reaction.

However, the easiest way to check for water in methanol is to measure the density.
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[*] posted on 15-4-2021 at 12:04


What is produced in a reaction is another matter. Mine was about solubility. Water elimination would be a completely different issue.

But, silly me, the density test. It stands right on point to the very anhydrous state.
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