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Author: Subject: Glyoxal Synthesis
morsagh
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[*] posted on 23-4-2016 at 10:50
glyoxal synthesis


Hi there, i am going to synthetise glycouril by reaction of urea, glyoxal, catalysed by P4O10 in aqeous solution (ref.: http://www.tandfonline.com/doi/full/10.1080/17518253.2012.71...) , and then polymerize to (6)cucurbituril with formaldehyde in conc. H2SO4. The only problem is i do not have any glyoxal so i want to prepare it by reaction of ethanol with nitric acid (maybe copper catalyst)... but i can´t find any reference to this method, does it really work, what are the yelds?
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[*] posted on 23-4-2016 at 12:49


Have you looked the couple of existing threads on glyoxal synthesis? Please use the search engine, you might find your answer.
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[*] posted on 23-4-2016 at 13:05


I found that thread but nothing usable. I would like to try HNO3 ethanol method but there aren´t written yelds etc..
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WGTR
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[*] posted on 23-4-2016 at 13:07


This has been a frustration of mine recently (in a fun sort of way). Making glyoxal isn't too difficult, I think. It's the workup and characterization that's difficult. Glyoxal polymerizes in traces of water, and isn't volatile up to its decomposition point unless first being dehydrated with phosphorus pentoxide. As long as glyoxal is kept in the gas phase, without being allowed to re-condense, it doesn't re-polymerize (I'll have to look for the patent that contains that information, I haven't tried that personally). It's slightly sensitive to "long" boiling in aqueous solution, so evaporation during work-up is usually done under reduced pressure, slightly above room temperature. Alcohol oxidation with nitric acid produces a mix of products, including glyoxal, glycolic acid, glyoxylic acid, oxalic acid, and acetic acid. Out of those, both glyoxal and glyoxylic acid are aldehydes, and give positive reactions to Tollen's reagent.

To answer your question about references, you can check on Google Books for "Experimental Chemistry for Junior Students, part 4", by J. Emerson Reynolds, published in 1887, pages 156-159. It explains the experimental procedure, as well as how to separate the products from one another.

Keep in mind that air conditioning didn't exist when the book was published, so the temperature of the room was merely recorded for reference. It might be possible to do the reaction faster, so long as the temperature can be kept low. A microchannel reactor design might be beneficial in this case. Also, the suggested calcium carbonate won't cause a Cannizzaro reaction with glyoxal, although calcium hydroxide will. Don't neutralize the reaction mix with something like sodium carbonate, because all of your glyoxal will end up as glycolate. Use ethanol to separate out the calcium salts, don't substitute with methanol or acetone. I tried acetone, and ended up with some strange, unidentified goop. The Tollen's test on that resulting mess was negative.

Getting rid of the residual nitric acid is a challenge, as it seems to stop reacting below a certain concentration. Evaporation merely concentrates it up to its constant boiling point, around 68% concentration. It's common to see what looks like a finished reaction, upon evaporation at warm temperatures to begin erupting suddenly in a furious boiling of orange fumes. That's one thing that I verified. Copper salts have been tried as a catalyst to reduce the nitric acid content to zero, but my volcanic eruptions have still happened while using copper salts in the reaction mixture. I don't know what to say about that, other than the catalytic method isn't apparently straightforward. It would seem logical to neutralize the excess nitric acid with calcium carbonate, but calcium nitrate is very soluble in all the generic alcohols and in acetone, so it will carry over with the glyoxal.

One idea to remove excess nitric acid, would be to first neutralize the reaction with calcium carbonate. After extraction with alcohol and then evaporation of the alcohol, proceed to an electro-dialysis stage in water. If calcium nitrate ionizes in alcohol (or with minimal water), then you can probably do this purification in pure or concentrated ethanol. The concept is simple. The anode and cathode compartments are packed with activated carbon, or some other electrically conductive carbon with high surface area (high surface area is important). The electrodes could be graphite. You're basically making an electric double-layer capacitor (a supercapacitor). This is intentionally a non-faradaic reaction. You don't want charges crossing the electrode/electrolyte interface, so the cell potential needs to be kept low, below about 0.5 volts. The positive and negative ions will adsorb on the surface of their respective electrodes, but I "DON"T THINK" the glyoxal should have any particular charge, so it can be flushed from the various compartments as soon as the cell current drops off close to zero.



[Edited on 4-23-2016 by WGTR]




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[*] posted on 23-4-2016 at 13:53


So what about separation by bisulfite after neutralization by CaCO3?
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[*] posted on 23-4-2016 at 14:46


It would have to be barium bisulfite instead of the sodium salt, if you intend to break the adduct later and precipitate the leftover salts. Obviously, you can't just simply distil off the glyoxal like you can with formaldehyde or acetaldehyde. Dilute sulfuric acid can be used to break the adduct and precipitate the barium, but it has to be done carefully. Excess acid will be painful to remove. Historically, lead acetate was used to remove traces of sulfate, and then, I think, dilute hydrogen sulfide was used to remove traces of lead.

Glyoxylic acid can also form a bisulfite adduct, so make sure that the reaction is neutralized fully before extracting with ethanol.

Dr. H. Debus wrote an article using some of these methods, and he was an early researcher, if not the discoverer of glyoxal. You can find it on Google Books, as The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, Vol. XIII, 4th series, published 1857. pages 39-49.




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24-4-2016 at 01:09
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[*] posted on 24-4-2016 at 09:53


I think that in synthesis of curcubituril sodium salts won´t interfere... Or yes?
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[*] posted on 1-11-2017 at 08:22


heat sucrose in conc. h3po4 to 100c using oil bath for control. Employ a sweep gas, N2 or CO2, and what distills off is predominantly a mixture of glyoxal and methylglyoxal. these are good reducing agents in precious metal recovery
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[*] posted on 1-11-2023 at 05:00
Glyoxal extraction from an OTC product


Some time ago I came across an OTC product that apparently contains glyoxal. It's some sort of cleaning solution for camping toilets i think. I'm not into camping so I don't know what exactly it's used for. I'm gonna try to insert an image of said product here.
san-hy-sol fluid 8000.jpg - 33kB
According to the MSDS this stuff has 0,1-1% of glyoxal in it. Judging by some experiments I've done it's somewhere in between. Assuming 0,5% of this solution is glyoxal there would be 12,5g of glyoxal in the 2,5l which I got for 9€. Not quite the best deal on glyoxal but I'm trying to extract it nonetheless so here's the best of my results so far:

I started with 500ml of solution which i boiled down to a slightly thick liquid. The starting material is mostly water with some blue dye, limonene, detergent and other stuff in it. After boiling it down I added a solution of sodium metabisulfite made by dissolving 5g of the latter in a mix of 33ml H2O and 22ml EtOH. This was then stirred for 3h and a white precipitate of the bisulfite adduct of glyoxal formed. I filtered it off the next day and washed it with ethanol.
Now to turn it back into glyoxal it was suspended in water, 10ml of 20% HCl were added and the mixture was heated on a water bath with the beaker covered with plastic wrap to avoid evaporation (basically a reflux for lazy people). HCl slowly decomposes the bisulfite adduct releasing SO2. After 2 or 3h of heating I removed the plastic foil and let it evaporate down. I added some water back in after a while to hopefully remove excess HCl.
When most of the liquid was gone the solution started to give off white fumes which was probably just excess HCl but i was afraid of my glyoxal evaporating so I took it off heat and shot in a generous amount of EtOH. This made a bunch more salt precipitate out. Then some sodium bicarbonate was added to the mix in order to neutralize leftover HCl. Undissolved salts were filtered off and washed with more ethanol. The solution was once again evaporated on a water bath until all the ethanol was gone. A few ml of liquid remained which should be mostly glyoxal.

It's flammable and partially burns up with a blue flame. Some water is left behind which leaves a white solid upon drying. This solid is probably some sort of hydrated glyoxal oligomer as it mostly decomposes and disappears into smoke when heated. I suspect the material I ended up with is just very wet glyoxal. It faintly smells like formaldehyde which is apparently what glyoxal smells like.

[Edited on 1-11-2023 by BAV Chem]




If in doubt, try it out.

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ChemPlayer videos: https://archive.org/download/ChemPlayer
Organic Syntheses: http://orgsyn.org
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[*] posted on 1-11-2023 at 08:39


Well done BAV Chem! For some reactions you can use directly the adduct of glyoxal with bisulfite like o-phenylenediamine -> quinoxaline https://orgsyn.org/demo.aspx?prep=CV4P0824
I see your source is a German product. I ordered some glyoxal from Germany from https://shop.es-drei.de/aldehyde/12132/glyoxal-loesung-40-in...
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