Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: doughpat on November 19, 2014, 08:04:08 AM
-
Sitting here drinking a cup of decaffeinated coffee which claims to have been processed using "only 100% natural CO2".
I've always understood CO2, due its linear shape, to be totally non-polar. I would imagine caffeine is at least moderately polar, given it's ketone groups. It is clearly soluble in water, otherwise this coffee would be a pretty pointless addiction!
So: If "like dissolves like", how can non-polar CO2 be used to (somewhat selectively) extract polar caffeine from the huge mixture of compounds in a green coffee bean? Seems like dispersion forces would be both insufficiently strong and very unselective.
This site, http://www.coffeeconfidential.org/health/decaffeination/, just gives a general overview that CO2 is used, but doesn't reconcile the conflict that I am observing.
-
The statement instead might have read as follows: "using only 100% natural SUPERCRITICAL CO2".
Does this help?
-
Thanks for that--but no, I'm afraid I still don't understand why that would make a difference. Is the solubility of caffeine higher in liquid CO2 than gaseous?
-
Please see the subtopic entitled "Supercritical Carbon Dioxide Processing" in the following online reference:
http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Phases_of_Matter/Supercritical_Fluids/Case_Study%3A_Removing_caffeine_from_Coffee
Then, for an exposition that may tell you more than you want to know about this subject, please see:
http://www3.nd.edu/~enviro/design/caffeine.pdf
Hope this helps.