*For more cool stories, pictures, and videos of chemistry demonstrations, click here* It’s the extraction lab this week in the OChem lab I’m TA’ing. It’s a straightforward aqueous base extraction of an acidic unknown from a neutral impurity. Acidify, filter the precipitate, and you’re done. I was trying to come up with a demonstration for the lab. I thought about extracting caffeine from coffee or tea leaves, but that would take a while, and isn’t all that visually appealing.  I’ve only got a few minutes in my pre-lab lecture time. So I looked around for a while, and finally found this paper by James Hutchison from the University of Oregon (doi:  10.1039/b405810k).  They suggest a new lab for undergraduates involving the extraction of D-limonene from orange peels using liquid carbon dioxide.  That’s right, I said liquid carbon dioxide. The premise: create a removable filter using copper wire and filter paper to jam into the bottom of a disposable centrifuge tube.  Add grated orange peel.  Add crushed dry ice.  Cap the centrifuge tube tightly (but not TOO tightly! The tube needs to be able to vent so as not to EXPLODE!) and immerse in warm water (T = 40-60 degC).  The pressure rises (naturally) and the temperature increases and you jump into the liquid portion of carbon dioxide’s phase diagram (click for larger) The liquid carbon dioxide percolates through the orange peels and extracts the limonene.  the oil-in-solvent...