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.