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Topic: extracting an aldehyde into the aqueous layer?  (Read 277 times)

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Offline Babcock_Hall

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extracting an aldehyde into the aqueous layer?
« on: March 05, 2020, 09:12:22 AM »
It looks as if an aldehyde starting material has a similar Rf on silica TLC, relative to a vinyl sulfone that we made via a Knoevenagel reaction of the aldehyde.  It occurs to me that we might be able to extract the aldehyde into water if we make a water soluble derivative and thus make our purification easier.  I have seen papers in which aldehydes are converted into a derivative with bisulfite for purification and storage IIUC.  However, I do not recall seeing this done for the sake of getting rid of an unwanted aldehyde.  Thoughts?
« Last Edit: March 05, 2020, 09:31:57 AM by Babcock_Hall »

Offline pgk

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Re: extracting an aldehyde into the aqueous layer?
« Reply #1 on: March 05, 2020, 12:05:51 PM »
You can easily get read of an unwanted aldehyde, by washing (extracting) your organic solution several times (say 4-5 times) with an equal volume of a saturated aqueous sodium bisulfite solution. I have done this and it works perfectly.
Hint 1: Each washing (extraction) must take 5 minutes, at least.
Hint 2: If your product has the tendency to pass into the aqueous phase, you use lower amounts of saturated aqueous sodium bisulfite solution and wash for 3 times.
Hint 3: Saturated aqueous sodium bisulfite solution (NaHSO3) is prepared by adding sodium metabisulfite powder (Na2S2O5) into water until precipitation.
But attention! Solvation of NaHSO3 and Na2S2O5 in water, are endothermic and cool the solution, which decreases their solubility. Thus, precipitated NaHSO3 solutions that are quickly prepared, are not really saturated though seeming to be.
In order to avoid this, you add slowly small portions of Na2S2O5 into water and wait until the temperature equilibrates with the ambient one (by putting your hand on the flask). Then, repeat it several times until a precipitation that doesn’t get colder, any more.
It demands patience. 
Hint 4: Do not warm (Le Chatelier principle, etc.) during preparation because 2 NaHSO3 thermally decompose to Na2SO3 + SO2 + H2O.
« Last Edit: March 05, 2020, 12:27:42 PM by pgk »

Offline phth

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Re: extracting an aldehyde into the aqueous layer?
« Reply #2 on: March 08, 2020, 10:32:18 PM »
You can easily get read of an unwanted aldehyde, by washing (extracting) your organic solution several times (say 4-5 times) with an equal volume of a saturated aqueous sodium bisulfite solution. I have done this and it works perfectly.
Hint 1: Each washing (extraction) must take 5 minutes, at least.
Hint 2: If your product has the tendency to pass into the aqueous phase, you use lower amounts of saturated aqueous sodium bisulfite solution and wash for 3 times.
Hint 3: Saturated aqueous sodium bisulfite solution (NaHSO3) is prepared by adding sodium metabisulfite powder (Na2S2O5) into water until precipitation.
But attention! Solvation of NaHSO3 and Na2S2O5 in water, are endothermic and cool the solution, which decreases their solubility. Thus, precipitated NaHSO3 solutions that are quickly prepared, are not really saturated though seeming to be.
In order to avoid this, you add slowly small portions of Na2S2O5 into water and wait until the temperature equilibrates with the ambient one (by putting your hand on the flask). Then, repeat it several times until a precipitation that doesn’t get colder, any more.
It demands patience. 
Hint 4: Do not warm (Le Chatelier principle, etc.) during preparation because 2 NaHSO3 thermally decompose to Na2SO3 + SO2 + H2O.
I was gonna say this. 10.1021/acs.oprd.7b00231

Offline pgk

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Re: extracting an aldehyde into the aqueous layer?
« Reply #3 on: March 09, 2020, 01:45:10 PM »
The recently reported protocol is more effective, as being faster and obviously leading to higher yields.
Besides, the use of a minerally-saturated aqueous solution, permits the extractions with a water-miscible solvent.
But on the other hand and although it worths a try, my personal experience is rather poor results whenever I have tried the said kind of extractions with THF or THF/toluene.

« Last Edit: March 09, 2020, 02:28:36 PM by pgk »

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