Rich_Insane
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What happened here????
I made a solution of 1 M NaOH in EtOH about a week or two ago..... I accidentally left the stir bar in (highly doubt that has much to do with
anything). The solution is now golden-yellow. What happened? I'm scared of opening it now.
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aonomus
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NaOH solutions corrode glassware, so its generally bad practice to leave a solution in beakers for terribly long.
As for the stir bar, its coated in teflon, I doubt any amount of NaOH/NaOEt could corrode that. Maybe there are some contaminants on your glassware
that gave it the colour?
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entropy51
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Was it really EtOH? Or the denatured stuff containing all manner of other junk that can react with NaOH?
People use that mixture for soaking glassware to clean it. It always turns dark after a while.
Safe to open. You didn't make sarin or anything. Please wear eye protection. That mixture will blind you in a nanosecond if it
gets in the eyes.
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UnintentionalChaos
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Probably polycondensed crap from ethanol oxidation to the aldehyde and subsequent aldol condensations. A little bit can make a lot of color.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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entropy51
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But aldol is colorless. You think further condensation leads to colored compounds? My recollection is that KOH in pure EtOH doesn't turn dark. But
I might try it to test my senescent memory!
Edit: For what it's worth, I added 0.25 g NaOH to 5 mL of Everclear EtOH and to 5 mL of denatured EtOH. After about 15 minutes, the Everclear was
still colorless, the denatured was distinctly lemon yellow in color. I will see how this changes over time.
[Edited on 24-10-2009 by entropy51]
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DJF90
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I've seen ethanolic KOH that was very yellow brown - at the time, when I asked about it I was told its something to do with the aging of the solution.
I suspect this is what you are also experiencing.
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Rich_Insane
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It's 95% EtOH -- I'm not sure whether it's denatured or not, as this is at work. I don't think the stir bar has anything to do with the color. But
this wouldn't be really impure -- at most there'd be a little MeOH or Denatonium.
Either way, i'm just going to discard it.
EDIT: I added a little 6 N HCl... there was no reaction! No bubbling or fizzing. Usually when I add a little bit of HCl there's at least SOME physical
action going on..... weird. I discarded it anyways.
[Edited on 24-10-2009 by Rich_Insane]
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UnintentionalChaos
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Quote: Originally posted by entropy51  |
But aldol is colorless. You think further condensation leads to colored compounds? My recollection is that KOH in pure EtOH doesn't turn dark. But
I might try it to test my senescent memory! |
It's magical tar. It's not outlandish to imagine a series of aldol reactions, oxidations, and condensations that lead to a series of conjugated double
bonds, and such, which may function as chromophores. Sure, the odds may be against it, but if the products are very dark, and you have 600 billion,
trillion atoms (1 mole) kicking around a beaker, you're likely to get some visible color.
All that is needed to test is some ethanol and KOH. Sparge air through the mix for a day or so and watch for color change. or we could just reflux it
under an oxygen atmosphere for a while.
[Edited on 10-24-09 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Nicodem
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Something similar was already discussed time ago: http://www.sciencemadness.org/talk/viewthread.php?tid=6434
Most recently there was even a JACS paper published about aerobic oxidation (this turned out only after publication!) of alkoxides to carbonyl
compounds: http://www.sciencemadness.org/talk/viewthread.php?tid=12559
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Rich_Insane
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I also noticed that a 100 mM solution smelled like apples instead of ethanol when I dumped it (due to age, not color).
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entropy51
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| Quote: Originally posted by entropy51 | My recollection is that KOH in pure EtOH doesn't turn dark. But I might try it to test my senescent memory!
Edit: For what it's worth, I added 0.25 g NaOH to 5 mL of Everclear EtOH and to 5 mL of denatured EtOH. After about 15 minutes, the Everclear was
still colorless, the denatured was distinctly lemon yellow in color. I will see how this changes over time. |
After one week, the NaOH in denatured ethanol is dark orange in color, while the similarly treated Everclear ethanol is still
colorless.
I think the compunds in the denatured EtOH may be responsible for the color change.
[Edited on 1-11-2009 by entropy51]
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hissingnoise
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A possible culprit could be pyridine?
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entropy51
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I was thinking of pyridine too, but I checked and the denatured I used is Formula 19, which according to Merck Index is methyl isobutyl ketone and
kerosene.
Aldol condensation with the ketone perhaps?
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