killswitch
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Best method for cleaning esters?
I use the standard bicarb+brine method for deacidification and dessication, but was wondering if there might be a better method and was wondering if
anyone could spot potential problems with the following:
Dump the acid/nitrate mixture into a large bucket or jug (which must be plastic or glass, not metal) of distilled water. Your product will be a blob
that has sunk to the bottom of the tub. Some of it will likely also be floating on the surface of the water, with the appearance of lard in soup. Suck
these up with a pipette and release them below the surface.
Next, pour out most of the water, but not so much that the product starts to float to the top and reform those pesky blobs.
Next, make a warm (35-40 Celsius) solution of 10 parts distilled water to 1 part acetone. Add baking soda to the mixed solvent until no more will
dissolve, then pour the solvent into the wash bath through a coffee filter. Stir to ensure adequate mixing. The blob of product should become slightly
smaller and much runnier. Allow it to sit for about six hours.
Check the pH with litmus paper. If it is still acidic, add more soda water/acetone and wait. Once it is neutral, take a pipette of distilled water,
position the mouth well beneath the surface, and squirt to precipitate some of the dissolved ester. Repeat this step until no more product appears.
Then pour off most of the water.
Next, heat distilled water to 35 to 40 Celsius and dissolve as much salt as possible. Pour the hot saltwater into the washbath through a coffee filter
(that way the caking agent and other particulate matter does not pass through). Allow the ester to sit until it is no longer milky. Check the pH one
final time. If it is acidic, add more bicarbonate and allow to stand until it is no longer acidic. If it is neutral, remove the ester from the water
via pipette. If you will be storing it for any extended time, or transporting it via vehicle, add 4 parts acetone or methyl ethyl ketone for every 6
parts ester, and a miniscule dusting of sodium bicarbonate (roughly what you get from dusting the tip of your index finger and thumb, then rubbing
them together over the container)
I have not personally tried this method and am worried about spent acid possibly reacting with the acetone.
Another idea I had (which is less practical) would be to decant off as much water as possible, remove what's left via pipette, then add MEK to
partially dissolve it and a few drops of sodium methoxide. Any comments on this method?
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Motherload
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Why sodium methoxide ?
A strong base like that might end up methylating and replacing some of the -NO2.
Same with NaOH etc .... Might turn it back to the corresponding alcohol/polyol etc.
NaHCO3 works just fine and the effervescence is a good indication of the neutralization.
"Chance favours the prepared mind"
"Fuck It !! We'll do it live !!"
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killswitch
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Quote: Originally posted by Motherload  | Why sodium methoxide ?
A strong base like that might end up methylating and replacing some of the -NO2.
Same with NaOH etc .... Might turn it back to the corresponding alcohol/polyol etc.
NaHCO3 works just fine and the effervescence is a good indication of the neutralization. |
The methoxide wasn't really a serious proposal. My main thought was, it's a liquid, and thus no friction. But yeah, if there were any trace water or
methanol in there, you'd get the methyl ester and sodium nitrate. Classic Sn2.
/slaps self in face.
But I'm more focused on the acetone/soda water approach. Any side reactions with the acetone? I know that concentrated mixed acid turns acetone into
mesitylene, which then nitrates extremely quickly and sends plumes of NO2 into your face. But does dilute aqueous acid do anything odd? It'd protonate
the enol, wouldn't it?
[Edited on 26-2-2013 by killswitch]
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Motherload
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Depending on the nitrate ester you want to neutralize .... Sodium carbonate isn't particularly soluble in acetone. So you will still have 2 phases.
If it is a liquid ... I'd personally just use an aqueous carbonate solution.
"Chance favours the prepared mind"
"Fuck It !! We'll do it live !!"
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