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Things I Won't Work With

Things I Won’t Work With: A Nasty Condensed Gas

If you cool things down enough, you can turn almost anything into a liquid (or into a solid, if you’re really insane about it.) Chemists use liquid ammonia fairly often, for example, though it’s been some years now since I’ve needed any. People outside the field think of the aqueous solution of ammonia gas (household ammonia) when you say “liquid ammonia”, but I’m talking about the pure stuff. Cool the gas down below about -33 C, and you’ll condense it out to a clear liquid that’s sort of like a thinner version of water.
It’s easy enough to do, with an ammonia tank and a condenser full of dry ice. But once, over twenty years ago, I had a chance to see someone use one of those rigs to condense something a bit more exotic: pure hydrogen cyanide. That’s another one that people confuse with the aqueous solution. But pure HCN has a fairly high boiling point, for such a small molecule, and condensing out is no problem – as long as you have more nerve than you have sense.
The fellow doing it was down the hall from me in graduate school, and he was doing an obscure reaction which forms a geminal dinitrile, which themselves are rather obscure compounds. (That’s probably because this bug-eyed route is the best way to make ’em.) He was dressed in full suit and respirator gear, for which he’d had to get trained. Everyone else had cleared out of the lab, but someone was watching him at all times from the hallway, just in case.
I thought to myself, “When am I going to get the chance to see pure liquid HCN again?”, and went down to see, ready to bail out if anything started going wrong. It looked just like ammonia, clear drops rolling down the cold condenser and dripping into the round-bottom flask below. But there was enough HCN in there to kill off the lot of us, if (im)properly handled.
I’ve worked with plenty of cyanide since then, and even plenty of reactions that have produced small whiffs of HCN vapor. (As I think I’ve mentioned, it doesn’t smell as much like almonds as it’s said to, in my opinion.) But I doubt very much if I’ve worked with enough of it to match the amount that I saw in that flask, that day – there must have been a couple of moles of it in there. A lifetime supply that was, in many sense of the word. . .

8 comments on “Things I Won’t Work With: A Nasty Condensed Gas”

  1. Harry says:

    Oddly enough I used to know a fellow that actually made pure HCN on a kilo basis. He had one customer that bought about 25kg/year.
    As you might expect he made it quite simply by adding Sufuric Acid to Sodium Cyanide and condensing the resulting HCN. He actually purified it as he made it by allowing the condensate to reflux in a 10 plate Oldershaw column, and then taking off only the pure HCN.
    Like you, I made a point to watch this once from a a safe distance. It was fascinating albeit a bit macabre to watch HCN refluxing.
    He actually made the stuff for years with no trouble, but I recall thinking that no matter what he was charging, it wasn’t enough.
    BTW I really enjoy the lab tales- I’ve been in the custom Organic synthesis business for over 20 years, so we have some experiences in common.
    Have you ever handled organoselenium compounds?
    They have the most aweful odors I have ever experienced, putting mercaptans and diamines like cadaverine to shame.

  2. Chris Hoess says:

    Hmmm. I seem to recall that the Org. Synth. prep for HCN recommends that the operator smoke during the procedures, as the tobacco apparently sensitizes you to the almond odor and lets you detect leaks at a much lower level. Times have changed…

  3. Whoa! Got a reference for that Org Syn prep? That would be one for the group room lunch table.

  4. Stewart says:

    Sure enough, it’s right there. Org. Synth. Coll Vol. 1, p. 314. Available on the web at
    The original reference for the smoking suggestion is given as Gattermann, Ann. 357, 318 (1907).

  5. Derek W says:

    Its also amusing (frightening) to me that ammonia was used as a refrigerant early on. Worked ok, I guess, unless there was a leak. (Google “icy ball” for one example.)
    One page notes how this low-tech approach is being recommended for modern day use in third world countries.

  6. hound says:

    unfortunately i remember standing too close to a bottle of ammonia i opened while it was on the shelf. Instant immune system failure and sinus infection.this happedened once working with CCl4 also.
    I’ll take your word on the almond odor;)
    My vote for worst odors – either pyridine or carbon tetrachloride.

  7. hound says:

    derek, i believe one might have to admit that perhaps ammonia would be safer to the ozone if leaked than other refrigerants.

  8. Lawrence B. Ebert says:

    Of the mention of ammonia as a refrigerant, recall that Einstein and Szilard got a patent in the area. Motivated by a news story stating the ammonia refrigerant leaked from a home refrigerator and killed a family, Leo Szilard and Albert Einstein believed that their knowledge of thermodynamics and engineering would be useful in improving refrigerators. The device they designed was actually manufactured, but then freons came.

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