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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: UAphenix on October 03, 2005, 03:25:42 AM

Title: Caffeine why, sublimation and not recrystallization?
Post by: UAphenix on October 03, 2005, 03:25:42 AM
Can anyone explain to me why sublimation would be used to purify crude caffeine as opposed to recrystallization?  I reallize that caffeine doesn't boil, it does sublime though.  I may completely wrong here, if you can't tell i am to say the least completely lost.  Any ideas would be very helpful.  Thanks
Title: Re:Caffeine why, sublimation and not recrystallization?
Post by: Mitch on October 03, 2005, 03:50:31 AM
Its a better way to remove impurities.
Title: Re:Caffeine why, sublimation and not recrystallization?
Post by: UAphenix on October 03, 2005, 11:26:09 AM
Thanks, what makes sublimation a better purifier than recrystallization?  I have been looking all over the web to find a comparison of the two, but have not had any luck.
Title: Re:Caffeine why, sublimation and not recrystallization?
Post by: xiankai on October 09, 2005, 05:58:02 AM
crystalisation relies on the partial precipitation of a salt based on the difference in solubility at different temperatures.

with sublimation however, u can be assured that all the substance will sublime, just like how water boils completely beyond 100oC