Bedlasky
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Dimethyl oxalate synthesis problems
Hi.
I today started second attempt to make dimethyl oxalate. First one was failure because when I wash dimethyl oxalate with ice cold water, I found that
dimethyl oxalate is better soluble in water than in methanol (which is strange for organic compound) and all solid dissolved.
After synthesis I did first recrystallization. Then I filtred solid dimethyl oxalate and check it's pH with pH paper. It was around 1. So I decided to
do the second recrystallization. I checked pH of this solution and it is between 1 and 2. Is there better method how to remove acid? I still have
liquid from all filtrations, so I was thinking about adding water in to this and than exctraction with ethyl acetate. Then few washings with saturated
sodium bicarbonate in separatory funnel and finally evaporation of the solvent.
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Tsjerk
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Did you use methanol for the recrystallization? I don't think washing ethyl acetate with water is going to work, as your product will dissolve into
the water.
[Edited on 16-7-2020 by Tsjerk]
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Pumukli
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Which recipe are you trying to follow?
There surely are synthesis descriptions for this compound and as one of my teachers told so many times: no need to reinvent the wheel.
I think there's a description on OrgSynth too, it should be a reliable source of info.
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Tsjerk
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I would add solid bicarbonate to the reaction mixture, heat until everything dissolves, hot filter and crystallize in a freezer.
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fusso
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Quote: Originally posted by Tsjerk  | | I would add solid bicarbonate to the reaction mixture, heat until everything dissolves, hot filter and crystallize in a freezer.
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I think K carb is better as both K carb and oxalate are more soluble than the Na salts.
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Tsjerk
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| Quote: Originally posted by fusso | | Quote: Originally posted by Tsjerk | | I would add solid bicarbonate to the reaction mixture, heat until everything dissolves, hot filter and crystallize in a freezer.
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I think K carb is better as both K carb and oxalate are more soluble than the Na salts.
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My idea is not to use water at all. The sodium bicarbonate, sodium sulfate (I assume sulfuric acid is used) and sodium oxalate stay undissolved in the
methanol. So theoretically only methanol and dimethyl oxalate pass the hot filtration.
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Bedlasky
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Most of the preparations I found on the internet use oxalic acid dihydrate, less methanol and too much sulfuric acid (at least in my opinion). Look at
this, other recipes are similar:
https://thosci.com/synthesis-of-dimethyl-oxalate/
So I little bit modify this preparation. I used:
24g anhydrous oxalic acid
50ml of methanol (+ cca 5ml, because I need to filtre the solution and wash flask little bit)
10ml of conc. sulfuric acid
Mixture in flat bottomed flask, boiling stones, reflux condenser, boiling for cca 30 minutes. After that transfer to the beaker, cooling it at room
temperature, than cooling in saturated NaCl solution from freezer for cca 1 hour (I changed cooling solution two times). Filtration, two
recrystallizations from methanol (first 40ml, second 25ml), beautiful needle shape crystalls, bad yield (I don't know how much because now it is still
wet), pH between 1-2 (so there is still acid).
[Edited on 16-7-2020 by Bedlasky]
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Bubbles
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My yield wasn't too great with this reaction too (50% or so), but I made a large batch and no effort was made to get a high yield. But I'd vacuum
filter after freeze precip, wash on funnel with a small amount of cold water, and recrystallize once from methanol.
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S.C. Wack
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The esters are made with distillation and without other acids. The simplest explanation for acidic needles would be that they aren't plates of neutral
dimethyl oxalate, and contain the acid and/or methyloxalic acid.
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markgollum
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I made dimethyl oxalate many years ago, I did it a number of times but never got a great yield, I remember that I never got it free of acid so I
changed to use much less sulfuric acid which seemed to be better. I recrystalized it from methanol. I regard it as an annoyingly moisture sensitive
product, the needle crystals would degrade from just the moisture content of the air. So I’d would have to bottle them as soon as possible once they
were dried from the methanol.
Since my purpose of making it was to react it with monoethanolamine, to get the NENO precursor I decided to try another oxalate ester. I found that
di-isopropyl oxalate was much easier to make in better yield, easier to work up and separate from sulfuric acid catalyst, and much easier to store for
many years (I still have most of it). I made it by refluxing anhydrous oxalic acid with 99% isopropyl alcohol, and just a small amount of sulfuric
acid, then slowly distilling off the water azeotrope. I vaguely remember doing a water and bicarbonate wash of the liquid ester and storing it with a
aspirin sized lump of fused calcium chloride to dry it. The reaction of stoichiometric quantities of isopropyl oxalate with ethanolamine (a plastic 2
ml pipette used to slowly add the ester to the amine) generates a lot of heat and crackles, hisses and pops since the liberated isopropyl alcohol is
the lowest boiling point component and the temperature rises to well above its boiling point if you don’t use cooling. Then the NENO precursor
crystallizes out seemingly pure, only a small amount of isopropyl alcohol is left to evaporate off by heating. I never tried nitrating the oxamide of
2-aminoethanol.
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S.C. Wack
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Well now I suppose if one is starting with an oxalate instead of the acid, other acids will come into play.
I searched OS CV's with the mention above but did not find it as it's under methyl oxalate and I searched for dimethyl. If Marvel says concentrated
sulfuric acid is the ticket who am I to doubt, but it doesn't make sense and it's the only oxalate ester synthesis I could find that isn't just the
alcohol and acid.
A brief google found little toxicity information, which is curious with the methanol and oxalic acid and all; obviously this is less stable than
dimethyl sulfate but I'm not sure what it takes for DNA methylation.
Heating and distillation decomposes the unconverted oxalic and methyloxalic acid to methyl formate and CO2.
[Edited on 18-7-2020 by S.C. Wack]
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kmno4
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I had a look at OS procedure, just out of curiosity.
It is really weird, it looks like O- methylation rather than classic esterification. Additionally, very large amount of H2SO4 makes purification
difficult, obtaining acid-free product is not so easy.
However, it works.
Procedure without H2SO4 (but only 40% yield) can be found (for example) in "Systematic Organic Chemistry" (Cumming/Hopper/Wheeler, 1937).
What surprises me: in both procedures, not very high excess of MeOH is used. Personally, I would use as least 5 moles of MeOH for 1 mol of oxalic acid
to increase amount of ester. In case of EtOH it works. But maybe it will not work in case of MeOH, because of some reasons.... Experiment is king 
Слава Україні !
Героям слава !
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S.C. Wack
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OS also mentions hydrogen chloride, and this is in Brewster et al.'s Unitized Experiments, where HCl is absorbed and the mixture cooled after 10
minutes and that's pretty much all there is to it.
Without other acids it should be possible to increase the yield by adding toluene after the reflux, distilling it off with stirring, and refluxing
again with more alcohol. One may use a substitute for toluene when making e.g. the ethyl ester, which is a good thing because crystallizing it out
will be more of a challenge.
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Syn the Sizer
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I went to check out this synth as well as the site, it had been a while since I was there and wanted to see what else he was claiming as his.
Pretty much the whole site give a 404 error and main page is now just a bunch of photos. I wonder if he was made to take the site down.
https://thosci.com/
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Bedlasky
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Few days ago this site still works.
Here are some videos:
https://www.youtube.com/watch?v=imtSH3OAdKE
https://www.youtube.com/watch?v=yHq1RK-Myow
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Syn the Sizer
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For sure, when you first made the post I checked out the synth just not the rest of the site. I had a few bookmarks I had saved months ago and tried
them after I found your link to the synth was dead. I then check the homepage and it was just photos.
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