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How Not to Do It

How Not to Do It: Solvent Stills

Several of us started in on a “stupid lab tricks” conversation at lunch the other day. When chemists get together, we always know that that topic’s available if we run out of things to talk about. Anyone with reasonable organic lab experience has a stock of favorites.

One of mine is a fellow grad student who was trying to save money by recycling acetone, the wash acetone that he used to clean out his flasks. He had a four-liter round bottom with a side-stopper on it, rigged up to a big distillation head, and the thing was always cooking away.

Of course, the acetone in the pot got nastier and nastier as time went on, as he kept refilling it with whatever gorp he washed out of his dirty glassware. During the time I knew it, it was a deep, opaque chocolate brown with sort of purple overtones – not the usual color you look for in your acetone supply. The stuff he distilled off was pretty decent, but even so. . .

Well, eventually this guy took a vacation (for the first time since I’d joined the group.) He took off for a few days, and turned off the still before he left. There it sat, just as ugly in repose, until he came back and flipped on the power to the heating mantle. All was quiet, for a while.

I was right around the corner when I heard it: a loud “PING-whUUUrrrsh – splattt!” This alarming noise was followed by a really fearsome stench, a knock-you-back brew of who knew how many stinky carbonyl byproducts (no doubt including, as fellow organic chemists reading this have figured, a generous helping of mesityl oxide.) I charged through this to find that the still had blown the side-arm stopper clear across the room – the pinging sound was its ricochet off the wall – and the foul brown concoction had come geysering out after it. The far wall was a Rorschach blot of dripping slime, the source of the eye-crossing aroma.

The problem – as those who’ve made similar mistakes well know – was when the heating was turned off. All the grunge in the pot had, for the first time in months, finally had a chance to settle down to the bottom of the flask. Where it coated the pile of boiling chips down there with resinous mung, rendering them useless. Which allowed the whole shebang to superheat once the power was turned back on, until something finally oozed aside long enough to allow the first bubble to form. And then, as Louis said, aprez-moi, le deluge.

A solid majority of lab-accident stories start out “We had this solvent still. . .” That’s why you won’t find any of them in any large industrial environment. It’s just not worth the opportunity to add to the story file!