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Topic: Purification problem  (Read 4414 times)

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Offline marcinosss

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Purification problem
« on: May 19, 2010, 01:36:35 PM »
Hi,

I've just done reaction with phenol; dimethyl disulfide and H2SO4. I want get 4-(methylsulfanyl)phenol ( white/almost white crystals. Unfortunately I've got pink oil, or white-red crystals when I recrystallizate from petroleum ether.
TLC is correct, HNMR too. I don't know how can I get rid of this pink contamination? ( It could be quinones I think).
 

Offline g-bones

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Re: Purification problem
« Reply #1 on: May 19, 2010, 02:24:15 PM »
How about column chromatography? recrystallization is valuable technique and can often get rid of most impurities.  sometimes, though, it may not get all trace impurities out.  When it comes to color, even very minor impurities can give significant color to a compound.  If your 1H NMR looks clean and the next reaction isnt insanely sensitive, you could just carry it on anyway and see if the reaction is significantly affected.  of course run it on a small scale if the other material is precious, but you may save yourself some time and frustration in the future if you find out that your next reaction is not that sensitive to whatever is causing the coloration.  You could also try trituration in which you wash the surface of the crystals with a non-polar solvent (hexanes, pentanes etc).  I have had success with this technique in the past.  Although, it maybe that if it didn't get pure with complete recryst. maybe trituration wont due it, but you'll never know until you try.  its easy and doesnt take much time at all.  If you find that the solvent isn't picking up much color try slightly increasing polarity.  for example, I have used 3:1 hex:acetone in the past and had success.  its just important to recognize the difference between washing off the color from the crystals and just dissolving your compound.  you will inevitably loose some compound this way, but when it works, its well worth it. 

Offline stewie griffin

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Re: Purification problem
« Reply #2 on: May 19, 2010, 02:45:17 PM »
Decolorizing carbon (charcoal) is also good for getting rid of colored impurites. Just don't add too much or your compound might stick to the charcoal as well.
http://www.sas.org/E-Bulletin/2002-08-09/features2/body.html

Offline marcinosss

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Re: Purification problem
« Reply #3 on: May 21, 2010, 08:34:45 AM »
Thanks a lot  :)
I've used activated carbon and it works.

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