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hask123
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[*] posted on 29-10-2018 at 08:36
Help Identifying Reaction


Can anyone help me identify what reaction is taking place?

I extracted some acetylsalicylic acid from aspirin using acetone, boiled off 85% of the acetone and then added a solution of sodium hydroxide to produce sodium salicylate and sodium acetate. I then refluxed the solution for an hour but there was some solid in the flask.

Here's the problem. When I filtered the solution (which was yellowish brown) it turned green. At first I thought my apparatus was dirty but after leaving it for a couple hours it went back to the yellowish brown colour. Then I shook it and it went green again.

Does anyone know what is going on here? I was thinking it might be some sort of reversible oxidation but i have no idea. Any help identifying this would be much appreciated.

Here are pictures of before and after shaking

20181029_123432.jpg - 5.5MB
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fusso
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[*] posted on 29-10-2018 at 09:25


First of all, what's the source of the chemicals? Did they state how pure they are?



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DavidJR
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[*] posted on 29-10-2018 at 09:37


In alkaline conditions, acetone has a tendency to undergo condensation reactions and polymerise into nasty gunk.
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CobaltChloride
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[*] posted on 29-10-2018 at 09:46


That's most certainly it. I know the color acetone tends to get after prolonged contact with sodium hydroxide and it is just like your solutions in the picture.
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hask123
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[*] posted on 29-10-2018 at 10:08


My chemicals are all OTC. aspirin from the store, nail salon "100%" acetone, hardware variety lye, and tap water. Guess it's probably the acetone polymerizing. Next time ill have to be more patient and properly dry or crystallize or by acetylsalicylic acid.

Thanks a lot for the input!
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DavidJR
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[*] posted on 29-10-2018 at 10:31


Personally I don't use acetone as a solvent very often as it is just too reactive. I use it for cleaning glassware (which it's pretty good at) but it wouldn't be my first choice for an extraction, recrystallization, or reaction solvent. Try using an alcohol instead (methanol, ethanol, or isopropanol are cheap and useful).

[Edited on 29-10-2018 by DavidJR]
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