BoroNar
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Metaldehyde to acetaldehyde
Managed to get some metaldehyde, bright white powder, burns cleanly, quality seems adequate.
Heating produces white fume, with "apple smell".
Acetaldehyde is needed for pentaerythritol, per orgsyn instructions acetaldehyde aqueous solution is used.
Tried dry distillation of 20g powder, didn't condense anything, even having ice-cold water in condenser(not below zero, about 4-5c) but smell was
coming out from gas exit tube.
Considering following options:
1. Dry distillation but with higher temperature, also driving air into gas scrubber, if nothing condenses, at least water will absorb gaseous
acetaldehyde.
2. Distillation with water, though tried at micro scale, not much soluble, but gets wet at least and will be evenly heated.
3. Distillation with acidified water, 1-2%? of sulfuric.
If somebody has experience doing something similar, or has experience to tell which way is most likely to have success, any information or guidance
would be appreciated.
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DraconicAcid
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I suspect the vapour pressure is too high, since you're only cooling it to 10 - 15 C below its boiling point. Maybe run the gas into ice-cold water
to get a solution?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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jackchem2001
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I would go for option 1 or 2. Option 3 seems a bit risky for polymerisation
A simple ideal gas/ideal solution VLE model predicts that, for a given mass of acetaldehyde, using 2.5x times the mass of water will give a mixture
with a bubble point around ~70 degC, so storing this is no problem.
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bnull
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Option 3 is the simplest. Metaldehyde is depolymerized by distillation from dilute acid, just like paraldehyde.
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BoroNar
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Thank you all for informaton and advices,
Meanwhile I tried first two options,
dry dist is defitinely not the way to go, some vapour comes but nothing meaningful, increased temperature and got sublimation on flask top and inside
tubing, leading to cold water.
Tried to dissolve into water, very low solubility, just floating even after hour of stirring. That semi-floating mass was set on boiling water bath
(for limiting temp below 100c) and allowed vapours into very cold gas washer bottle. Gasses were observed, but not very much. Most of metaldehyde
floated, neither dissolved nor converted to vapour. After 2 hours that floating mass begin yellow tinting and after 40 minutes got very yellow, like
sulfur. Unfortunately, due to my error, I couldn't measure water increase (if any) in gas washer. I was pushing vapour directly to washer, without
suckback trap... you know what is guaranteed to happen...
Left with acidified dist option, but I wonder if metaldehyde will dissolve in, if left floating, same result is almost guaranteed.
There is paraldehyde depolymerization process described on erowid:
https://www.erowid.org/archive/rhodium/chemistry/acetaldehyd...
using only conc. Sulfuric, but that trick didn't work on metaldehyde, got runaway and black mass from metaldehyde pile, somewhat like when playing
with conc. sulfuric and sugar.
I can't think how to adapt paraldehyde process to metaldehyde, latter is powder, not wanting to dissolve in water.
Will try this: make metaldehyde into water, no floating, use as much water as needed, warming a bit, then add sulfuric dropwise, make slightly
acidified solution about 1-2%. then do dist as usual.
I wonder why nobody has publicly documented this process, have been searching all around for last week, nothing could be found.
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