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MrDoctor
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Quote: Originally posted by Waffles SS  |
Anyway I want to introduce another interesting method for synthesis carboxylic acid anhydride by electrolysis.
Electrolysis by graphite anode and steel cathode of mixture:
Carboxylic acid + acetonitrile + catalyst (potassium thiocyanate) make anhydride
[Edited on 18-8-2025 by Waffles SS] |
I would have eaten my desk out of pure rage, had that paper been published in like 1970 or something and yet again such a valuable piece of research
had been sat on for 50 years before we (amateur chemists) found out about it. But luckily it was published in 2022, so my desk remains largely bite
free.
I am currently in possession of some tetrabutylammonium bromide, and can easily concentrate my 90% weed killer grade acetic acid to glacial for the
occasion. I think i will try this and report back, though, since the tetraethylhalide electrolytes yielded nothing at all, i wonder if maybe i need to
change out the bromide for something else?
Im not particularly comfortable with trying to synthesize thiocyanate, since there doesnt really seem to be a way around it without using cyanide, and
i dont understand its chemistry at all and see that it can potentially hydrolyze back to cyanide, and, if the cost is just efficiency or anode
lifespan, then i already have what i need right now.
now that being said, i also have a bit of a silly postulation, since potassium cyanate was shown to work, but not tested on graphite, just boron doped
diamond which performed universally worse than graphite. what if i stuck cyanate onto TBA? potassium cyanate performed terrible, but it did perform,
also these results were all from butyric anhydride formation not acetic, so idk how that translates, and if even the values are a yield cap since all
tests were done with 1.1F, not run all the way to determine where they top out, aside from a general statement that 70% is as high as it goes
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clearly_not_atara
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Ha, what an amazing method to end up on the end of a page. Nice find, Waffles.
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Waffles SS
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Thanks,
I also know better and more exciting method for synthesis Ac2O!
Do you have access to vinyl acetate or acetylene gas?are you ready for introduce another interesting method?(my favorite method )
Chemistry = Chem + is + Try
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chempyre235
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Not sure what country you live in, but Scientific Polymer has vinyl acetate for 8-10 cents/gram, depending on the quantity purchased.
"However beautiful the strategy, you should occasionally look at the results." -Winston Churchill
"I weep at the sight of flaming acetic anhydride." -@Madscientist
"...the elements shall melt with fervent heat..." -2 Peter 3:10
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Waffles SS
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Here the price of VA monomer is 2$ per kg
Chemistry = Chem + is + Try
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chempyre235
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Who sells it? If they're US, I might add to my list of suppliers.
"However beautiful the strategy, you should occasionally look at the results." -Winston Churchill
"I weep at the sight of flaming acetic anhydride." -@Madscientist
"...the elements shall melt with fervent heat..." -2 Peter 3:10
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Waffles SS
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My Vinyl acetate monomer made by Shazand Petrochemical Company
[Edited on 20-8-2025 by Waffles SS]
Chemistry = Chem + is + Try
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MrDoctor
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i have noticed here and there occasionally its mentioned acetic anhydride decomposes when boiled/distilled, could someone elaborate on this? im
currently distilling an AcOH/Ac2O mixture of unknown concentration and its kind of stuck at 123-125C, afaik the acid content should be dropping it
shouldnt be forming a stable constant boiling mixture, but it does have me concerned its somehow decomposing.
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clearly_not_atara
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I think there are other ways to separate them, like by crystallization. You could chill and mix with a light alkane or similar np. AcOH will ppt.
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MrDoctor
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it looks like ill have to try that. i think i finally managed to prepare a modest quantity of pure acetic anhydride to deliberately dilute and test
the feasibility of seperation from the acid. as for the odd behaviour i noted earlier, i believe thats just because where the curves meet in the
middle, a certain mixture of acid/anhydride is favored so it hangs around 125C for a long time.
I really want to see if its possible to isolate the acetic anhydride from around 500ml of 20% anhydride in acid. its the upper end of what glutaric
anhydride will get, or pessimistically what sulfobenzoic anhydride (made from saccharine) will get, and similarly, the lower end of what electrolysis
with thiocyanate in acetonitrile will give.
While on the subject, i dont recall if i read this in literature or if grok spewed it to me, but is there perhaps a salt that can be used to brine-out
the anhydride? the one recommended to me was anhydrous magnesium chloride. it seems logical that if you had a salt soluble in acetic acid and
specifically NOT soluble in acetic anhydride, that some amount would cause layering to occur. Or similarly allow for efficient seperation of acetic
acid/anydride from toluene since the 3 are miscible and form a ternary azeotrope of sorts.
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Alkoholvergiftung
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Why do you have an acid mix? Did you use the thermal cracking methode of glacial acetic acid. coincidence i searched patents of acetic acid anhydrid
and i found some patents on cracking glacial acetic acid vaposrs on silica gel catalyst at 700C and they wrote an yield of 54% anhydrid and the rest
is glacial acetic acid. If used80% acetic acid temperature for the cracking is 750C and yield is only 48%. Also an mix with acetic acid. If you can
separet them without problems maybe an interesting methode of making AcO.
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bnull
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| Quote: Originally posted by clearly_not_atara | | I think there are other ways to separate them, like by crystallization. You could chill and mix with a light alkane or similar np. AcOH will ppt.
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This, I believe:
Attachment: US1941951.pdf (347kB)
This file has been downloaded 8 times
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