Adas
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NaOH + lactic acid = strange smell
Hello guys,
I was trying to decarboxylate some lactic acid with NaOH. Here is what I did:
I put few pearls of NaOH into a test tube. Then I added some 80% lactic acid (food grade, brown-colored like vinegar). The NaOH has just been wetted
by it. Then I heated the mix on a candle flame. It started boiling, everything dissolved, and a clear liquid appeared on the sides of the test tube.
Don't know whether it was just water distilled off or ethanol, but when it touched the hotter part of the test tube, it boiled instantly. Then I added
some water to cool it down. There was a little "poof" due to the superheated NaOH solution. After this, I observed strange smell, which I know pretty
well, but can not identify. I think it smelled like dung-water or something like that.
What do you think, what caused the smell? Some kind of lactide formed? Or did the NaOH react with the coloring substance? Does anyone have time to
reproduce this little experiment? (Of course without putting water into the superheated liquid  )
Thanks for your time.
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vmelkon
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You said "it started to boil". Your lactic acid was a solution in water?
I think for decarboxylation to occur, water must be eliminated. The required temperature is probably above 200 °C or 300 °C.
The product should be ethanol. One way to test it is to measure density, boiling point, smelling it and also adding it to K2Cr2O7 which should become
green.
I don't have any lactic acid, so I can't do that experiment.
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Adas
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Quote: Originally posted by vmelkon  | You said "it started to boil". Your lactic acid was a solution in water?
I think for decarboxylation to occur, water must be eliminated. The required temperature is probably above 200 °C or 300 °C.
The product should be ethanol. One way to test it is to measure density, boiling point, smelling it and also adding it to K2Cr2O7 which should become
green.
I don't have any lactic acid, so I can't do that experiment. |
Yes, as I stated it is a 80% solution. I smelled it but I could only smell that strange smell I described. But if what you say is true, that it needs
200-300°C, then no decarboxylation could have occured. I want to know what caused that strange smell, though. It doesn't have any list of additives
so I can only wonder...
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morry-cule
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Perhaps it underwent a base catalyzed dehydrogenation and formed acrylic acid.
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Ozone
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That would be dehydration, and it is catalyzed by acid (to create water as a leaving group). My guess would be that you got CO2 and ethanol. It is
possible that other stuff (impurities) in your lactic acid may have been degrading (or reacting with ethanol) to create strange-smelling compounds.
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Nicodem
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In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.
Anyway, the mixture of pyrolysis products of sodium lactate is expectedly quite a complex crap. The first google hit would have told you that, if you
would've taken a minute to search for the literature. Ethanol obviously cannot form, because there is no mechanistic pathway for its formation. There
are however plenty of pathways for the poly-condensation products and their decomposition/decarboxylation/disproportionation products:
http://legacy.library.ucsf.edu/documentStore/b/k/j/bkj35e00/...
At lower temperatures, such as your melt of sodium lactate, lower molecular weight crap probably prevails. In any case, crap commonly smells like
dung, so that I would dare to say that the results of your uncontrolled experiment are in accordance to the theory of organic reactions.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Adas
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| Quote: Originally posted by Nicodem |
In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.
Anyway, the mixture of pyrolysis products of sodium lactate is expectedly quite a complex crap. The first google hit would have told you that, if you
would've taken a minute to search for the literature. |
I searched on Google but didn't seem to find anything useful.
Thanks for the replies, guys 
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DieForelle
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"Then I added some 80% lactic acid (food grade, brown-colored like vinegar)"
"it is possible that other stuff (impurities) in your lactic acid may have been degrading"
The two solutions of 85% Lactic Acid from 2 different vendors (a lab supplier and a wine making supplier) I've seen in my life were a light straw
color, not brown.
[Edited on 15-1-2013 by DieForelle]
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Adas
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| Quote: Originally posted by DieForelle | "Then I added some 80% lactic acid (food grade, brown-colored like vinegar)"
"it is possible that other stuff (impurities) in your lactic acid may have been degrading"
The two solutions of 85% Lactic Acid from 2 different vendors (a lab supplier and a wine making supplier) I've seen in my life were a light straw
color, not brown.
[Edited on 15-1-2013 by DieForelle] |
Yes, I meant that, I am sorry. 
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