It turns out that the teflon air-free stopcocks used in Schlenk-ware aren’t all teflon, they have little viton O-rings hidden under two teflon sleeve rings (=the green bits that provide the actual seal contact surface). And viton swells in acetone like a sponge…

After finishing a year-long scaleup project done with boiling conc. HCl, I had to overhaul my hood, because of all the corrosion. Long story short, the vacuum manifold glass parts went into a base bath, the O-rings and air-free stopcocks sat in a bucket with acetone. About an hour later, I noticed that the O-rings from manifold joints were already up to double in size. Those old swollen O-rings may eventually return close to their original size when they dry up. But all stopcocks from a long double bank manifold got ruined – the green teflon parts, stretched and lifted by the bulging viton from inside, are going to stay out of shape for good.

It is nice to learn that these teflon air free stopcocks used for all kinds of harsh chemistry actually won’t tolerate immersion in a solvent like acetone, DCM, THF. The ones I just killed cost $500 plus one week of wait-time to replace.