[doughpat]

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.

[OrgXemProf]

The statement instead might have read as follows: "using only 100% natural SUPERCRITICAL CO2".

Does this help?

[doughpat]

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?

[OrgXemProf]

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.