Keras
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What is the goo formed by adding KOH to crude diethyl ether?
Guys,
I recently made some diethyl ether using the hackneyed ethanol + sulphuric acid mixture. I washed the result with NaHCO3, separated it,
then let it stand over calcium chloride and went on to redistill it at 50 °C. Thought I would get some nice clean substance, so I added a few flakes
of KOH to take care of peroxides, and let the small bottle stand.
However, since then, the KOH has dissolved and formed a sort of reddish goo – well it’s not really a goo, more like powder and probably a reddish
liquid. That reminds me of what Nerdrage got in his video about purifying diethyl ether, so I guess my sample was far from pure. But anyways, does
anyone have a clue as to what exactly KOH reacts with and what is that red product? Sulphur something?
Thanks!
PS: I can get a bottle of anhydrous diethyl ether for about €20, I think I’ll quit trying to make it myself. It’s a nice experiment, very
didactical, but it’s not worth neither time nor hassle.
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Phthaloblue
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When diethyl ether is made this way, probably the product is contaminated with some acetaldehyde which formed from the oxidation of ethanol. When KOH
is added, it will catalyze aldol condensation and polymerization. If dehydration of these aldol products occurs, you could get unsaturated compounds
with visible color. So the red gunk probably formed from the aldehydes contaminating your ether.
I haven't made any ether this way, so this is only an educated guess. If you have access to an NMR machine or IR spectrometer, you could try
confirming the presence of aldehydes (or other suspect contaminants) in the raw ether and their absence after KOH treatment.
Add some BHT and maybe a few coils of copper to prevent peroxide formation, or else use the ether quickly!
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Keras
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Thanks for your answer! My ether is actually stored over KOH, and that goo formed in the course of a week or so.
I suppose I could get rid of it by redistilling the ether. Or I was wondering if the acetaldehyde could be oxidised further to acetic acid, then
neutralised with KOH and eliminated by washing with water. Of course I would then have to once again remove the residual water from the ether… :S
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Ubya
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Mood: I'm a maddo scientisto!!!
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Quote: Originally posted by Keras  | Or I was wondering if the acetaldehyde could be oxidised further to acetic acid, then neutralised with KOH and eliminated by washing with water. Of
course I would then have to once again remove the residual water from the ether… :S
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KOH already works quite well to purify it, sure you could use an oxidizer, but you would still need to wash the solution with a base and distill it to
remove everything else. KOH already partially dries it, so you would just need to filter and distill. i don't see any gains with your idea
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Keras
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| Quote: Originally posted by Ubya |
KOH already works quite well to purify it, sure you could use an oxidizer, but you would still need to wash the solution with a base and distill it to
remove everything else. KOH already partially dries it, so you would just need to filter and distill. i don't see any gains with your idea
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You’re right. I was thinking about oxidising it before you let it rest over KOH. That way you can neutralise the acetic acid with, say, sodium
bicarbonate. You wash the sodium acetate with water, and you get already a purer ether than you can then place over KOH.
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