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Things I Won’t Work With: Frisky Perchlorates

Perchloric acid almost makes my list by itself, although technically I can’t quite include it, since I’ve already used it. I used the commercial grade, which is 70% strength in water, and it’s pretty nasty stuff. It’ll chew through your lab coat and give you burns you’ll regret, as you’d expect from something that’s rather stronger than nitric or sulfuric acid.
But it has other properties. The perchlorate anion is in a high oxidation state, and what goes up, must come down. A rapid drop in oxidation state, as chemists know, is often accompanied by loud noises and flying debris, particularly when the products formed are gaseous and have that pesky urge to expand. If you take the acid up to water-free concentrations, which is most highly not recommended, you’ll probably want to wear chain mail, because it’s tricky stuff. You can even go further and distill out the perchloric anhydride (dichlorine heptoxide) if you have no sense whatsoever. It’s a liquid with a boiling point of around 80 C, and I’d like to shake the hand of whoever determined that property, assuming he has one left.
Perchlorate salts show similar tendencies. The safety literature is just full of alarming stories about old lab benches that had had perchlorates soaked into them years before and exploded when someone banged on them. They’re a common component of solid rocket fuels and fireworks, as you’d figure. As with other lively counterions, the alkali metal salts (lithium, sodium, etc.) are comparatively well-behaved, with things heading downhill as you go to larger and fluffier cations. I’ve used things like zinc and magnesium perchlorate, but I would refuse, for example, to share a room with any visible samples of the lead or mercury salts.
People have made organic perchlorate esters, too, which doesn’t strike me as a very good idea – unless, of course, you’re actively searching for a way to blow up your rota-vap. Which is exactly what happened in the paper I saw on the synthesis of ethyl perchlorate, as I recall. If you’d like to make your mark, this seems to be a relatively unexplored field. The problem is, the mark you’re most likely to make is in the nature of a nasty stain on the far wall.
Perhaps the most unnerving derivative I know of is fluorine perchlorate. That one was reported in 1947 (JACS 69, 677) by Rohrback and Cady. It’s easily synthesized, if you’re tired of this earthly existence, by passing fluorine gas over concentrated perchloric acid. You get a volatile liquid that boils at about -16 C and freezes at -167.3, which exact value I note because the authors nearly blew themselves up trying to determine it. The liquid detonated each time it began to crystallize, which is certainly the mark of a compound with a spirited nature.
The gas, meanwhile, blows up given any chance at all – contact with a rough surface, with tiny specks of any type of organic matter, that sort of thing. The paper notes that it has “a sharp acid-like odor, and irritates the throat and lungs, producing prolonged coughing”. My sympathies go out to whichever one of them discovered that. No, if it’s all the same to science, I think I’ll let others explore the hidden byways of perchlorate chemistry. . .

42 comments on “Things I Won’t Work With: Frisky Perchlorates”

  1. Robin Goodfellow says:

    Reminds me of stories I’ve heard about Chlorine Pentaflouride, which was, unbelievably, evaluated as a potential rocket fuel at one time. It is hypergolic with damned near everything, including all common fire fighting chemicals. It is even flammable in combination with glass (SiO2) as a fuel. The recommended procedure in case of fire is to seek shelter, preferably far away, and wait until it burns itself out.

  2. secret milkshake says:

    I have seen a step-by-step writup for ethyl perchlorate from Ba(ClO4)2 and EtOSO3Na. One could actually distill gram quantities of the material at reduced pressure. It is an oily liquid, unstable to moisture. A small drop of this material heated on a Bunsen burner likes to blow a hole right through a metal spoon.
    The maniac who described this prep (including the photos of his garage lab) noted that the material has a fruity smell and a sweet-musty taste. I guess he would not have to worry about Et-perchlorate being alkylating agent, tumors take years to develop so this would not play any role during his lifespan.
    On similar note- many years ago I tried to dry a wet acrolein with magnesium perchlorate. Suprise- the stuff disolved and became warm. “Oh, it is polymerising” I thought. So I started distilling the mix. There was bright orange flash in the flask and sound as if shuttle was taking off. The thing did not explode, just burned like a rocket and within seconds produced several buckets of very fine and greasy soot that settled all over the lab.

  3. bamh1 says:

    Might interest you to know that PCA, and at moderately high strength, is probably still used by your colleagues the biochemists. PCA is still used in lots of old protocols to precipitate proteins from solution, I assume because of the lyotropic properties of the perchlorate ion. We keep it cold, though. PCA is often substituted with trichloroacetic acid for this purpose, which is less explosive but otherwise about as friendly to have in the lab.

  4. MikeT says:

    I work in an analytical environmental laboratory where we use perchloric acid 70% to completely dissolve sediment samples. We mix some HClO4, HNO3, and some HF and then heat for 2 days to dryness. The hood we do this in has water washing the walls at all times to avoid perchloric dust buildup and explosion. You gotta have steady hands on those days.

  5. Derek Lowe says:

    MikeT, I didn’t know that’s how it was still being done. I guess the stuff has to be dissolved, no matter how you’re analyzing it, though. That’s quite a brew.
    Robin G, I think that fluorine perchlorate has also been looked into (and discarded) as a propellant. Those rocket guys leave few stones unturned.

    1. loupgarous says:

      You’re right. The discoverer of perchloryl fluoride was hired by Rohm and Haas in the 1950s and John Clark (in his classic Ignition!) describes the work done with it in propellant chemistry. It never yielded the sort of performance that other oxidizers did with the militarily important fuels, partly because of its high thermal coefficient of expansion – you had to store it in tanks that were much larger than optimum. It was a good additive to other rocket fuels for tactical missiles (it burned up free carbon in the contrails of other fuel-oxidizer combinations, making it more likely the missile’s launcher would live to fire another round),

  6. Denni says:

    Just dug out my old MSc thesis. I’m not a chemist, but I have great interest in cetaceans and the perils they face from pollution. My project was about the tissue distribution of mercury, methyl mercury and selenium in harbour porpoises.
    The method I followed used perchloric acid at 60% to ‘ensure that the organic matrix is broken down completely. Sulphuric acid is added to ensure dilution of the perchloric acid which can be explosive when heated’.
    It got entertaining when maintenance recalibrated the heating block without telling me 😉
    The courageous (and immediate) intervention of my supervisor prevented the roof being blown off te building.

  7. tom bartlett says:

    Reminds me of a friend who visited the Bartlett lab at Berkeley some years ago. They were looking at Xenon compounds, and everybody used weighing Teflon because weighing PAPER was too combustible. She ended up doing something a little safer– I think Plutonium chelators.

  8. Bob says:

    Mr Lowe,
    Several times I’ve seen you make reference to a compound’s smell, with a comment along the lines of “my symptathies to the poor schmuck who got to find out.” Other than the “wafting” technique, which is probably intended for relatively benign vapors, is there any “approved” method for figuring out how something smells? I’ve seen descriptions of certain chemical weapons as having a “fruity” smell. Was that a case of “Oh c**p! Well, for posterity, let me just say it smells like apples, with a hint of …. AARRGH!”?

  9. Derek Lowe says:

    That one’s worth a post of its own one of these days. But your suspicion that there is no safe way to smell some of these things is correct. The amount of some nasty chemicals that will allow their aroma to be experienced is well above the amount that will do damage; there’s no way around it.

  10. Hap says:

    When I first started being interested in chemistry, Cl2O7 and Mn2O7 seemed like interesting compounds with unusual similarity – both containing elements in the +7 (formal) oxidation state, one a metal and one a nonmetal, and both are reputed to be oily, brown, explosive liquids. I (fortunately) never had the chance to find out in person.
    Has anyone done Et2O-LiClO4 (5M) mediated Diels-Alder reactions? The thought of concentrated perchlorate in ether makes me nervous, but someone obviously used these conditions and made them work.

  11. Novice Chemist says:

    Yeah — I’ve tried those conditions for an intramolecular cyclization. No luck, but what I wouldn’t give to try them again.

    Worse yet, you get the LiClO4 soluble in Et2O by drying it (under vacuum under heat.)

  12. GC says:

    I held off on this to see if anyone mentioned it. Perchlorate salts are still ubiquitous as the counterions of certain dyes (laser dyes being the ones with which I’m acquainted), presumably because of their solubility and decreased tendency towards ion-pairing. These days I am more likely to do a Cl->BF4 or Cl->PF6 exchange, but I’ve had bosses who were educated as recently as the 70’s and 80’s still insist perchlorate was a superlative counterion to be playing with. Mahalo anyway, but some other time. That said, I inevitably end up dealing with old Spectra-Physics dyes that are perchlorates (the rhodamine series comes to mind, but they are legion).

  13. Paul Dietz says:

    While fluorine perchlorate is nasty, the related compound perchloryl fluoride (FClO3) is quite stable and not highly reactive, and was considered for a while as an oxidizer in rocket propellants.
    Other exotic rocket oxidizers include nitrogen trifluoride, hydrazine tetrafluoride, bromine heptafluoride, and oxygen difluoride. The nitrogen-containing oxidizers work well with boranes, since the nitrogen reacts with boron yielding boron nitride.

  14. bamh1 says:

    When I was a grad student 25 years ago, I did some perchloric acid hydrolysis of DNA to analyze UV photoproducts. I put the DNA sample in a piece of glass tubing with a fused bottom and about half an mL of 70% perchloric acid and sealed the other end of the tube with an open flame torch! I must have done hundreds of these, often a dozen or two at a time working alone in the lab at midnight so that the samples would be ready for analysis the next day. The sealed glass tubes were put in metal jackets and placed in a 175 degrees C oven for a couple of hours to perform the hydrolysis. The prof explained (with some chagrin, based on past experience) that the metal jackets were essential because if there was some invisible flaw in the glass seal the glass tube would burst when it got up to temperature, and the kinetic energy released would cause a “popcorn” type effect that would burst the other tubes in the oven as well. (The DNA was labeled with tritium and 14C). After the glass hydrolysis tubes had cooled down, I opened them by scoring one side and breaking the tube with pressure from my thumbs below the score. This was done in a chem hood and the pop was sufficiently impressive that other people working in the lab or going down the hall would stop and watch. Yet another reason why I wonder how I survived grad school.

  15. Coracle says:

    Heh, I was reading the nature article on safety in chemistry and thinking of this blog, and there you are, quoted!

  16. Harry says:

    Perchlorates always make me nervous, as do most other high-strength oxidants.
    We used to do an oxidation (22 liter scale) using 15% Hydrogen peroxide in THF which always had me on edge. The other, more classical approach to the same product involved white fuming Nitric acid- which is not much (if any) more reassuring.
    We never had any problems, but fortunately for my potential ulcers, we discontinued the product.

  17. DrShawn says:

    The above comments about the perchlorate anion’s wonderful properties are right on the mark. As both a synthetic chemist and an electrochemist, I can vouch for the versatility and usefulness of the perchlorate anion. There are simply times when perchlorate is far too useful to be written off for its safety hazards. BF4- and PF6- are okay, but both are readily hydrolyzed under ambient conditions to form HF, which if you’ve ever stored salts of these in a glass vial shows up by a halo of etched glass just above the salt.
    Perchlorates do have a nasty reputation, and deservedly so, but they come primarily from highly concentrated acid-organic mixtures or anhydrous organic perchlorate salts. For example, alcohols and concentrated perchloric acid readily form alkyl perchlorates, which tend to detonate violently if you look at them wrong. By the way, much confusion and mis-information comes from the poor recognition of the difference between concentrated perchloric acid and concentrated perchlorate ions from perchlorate salts. Of course, what cation is coupled to the perchlorate, makes every difference in the world. I routinely work with new organic perchlorates, and we continually test these by burning them in concentrated and dry forms to determine the hazards of working with them. They are surprisingly uninteresting (non-explosive). One easy way to test shock sensitivity is to hit a solid pellet of material with a hammer. Of course we use a blast shield and protective gear during all or our testing.

  18. highlyreactive says:

    Is this a good time to mention the infamous PEPCON disaster? Was a plant that manufactured aluminum perchlorate used for rocket fuel. The whole plant blew up. Video of the explosion. Note the shockwave!

  19. DrShawn says:

    Correction. The PEPCON plant manufactured Ammonium perchlorate NOT Aluminum perchlorate. As my post above points out, the cation makes all the difference in the reactivity of the ion pair. Ammonium perchlorate is rocket fuel; it is the solid propellant used in the SRBs of the Space Shuttle.
    According to the Wikipedia the plant had ca. 8.5 million pounds of ammonium perchlorate on site when a fire (from welding) broke out that caused a series of explosions.

  20. Dav says:

    Secret milkshake: If we are thinking about different people, I also know someone who made ethyl perchlorate in his garage, without incident, however that was at atmospheric pressure with barium ethyl sulfate and barium perchlorate.
    DrShawn: In the paper or Meyer and Sporrman who first discovered the alkyl perchlorates they state that they cannot be synthesized by the acid and alcohol.
    Hap: Mn2O7 is not too bad, I semi-regularly use in demonstrations(usually diluted with conc. sulfuric) to demonstrate the power of oxidizing agents. It also makes an awesome mix for cleaning glass without the toxicity issues of using chromic acid, if proper precautions are observed.

  21. DCL says:

    Years ago, I worked in an analytical lab supporting various chemical products. One of them was the electrolytic production of tetramethylammonium hydroxide in a closed-loop system.
    After several weeks operation an impurity in increasing concentration was observed, that was finally identified as a perchlorate.
    Soon after, the electroytic cell exploded, took out a brick wall and injured several workers, though none fatally.
    I can still remember the sound of the concussion hitting my chest, running down to the plant to see several guys under the emergency shower.

  22. FabioC. says:

    Wow, as a graduate synthetic organic chemist – with a penchant for dodgy chemicals – and soon-to-be chemical engineering PhD, I find this most fascinating.

  23. DrB says:

    This thread brought back memories of junior high school in Calgary when I was part of a group of geeks who had free run of the chemistry lab after school. It was before Halloween and one of the students wanted to mix up some KNO3 and sucrose to make smoke bombs. There wasn’t any KNO3 on the shelf, but there was a large bottle of NaClO4. As the original recipe called for sucrose and an oxidizer, it seemed reasonable to substitute NaClO4 for the NaKNO3. I was in the far end of the lab while the person was using a mortar and pestle to grind together the sucrose and NaClO4 in quite a large mortar. I recalled looking back at the large pile of white powder sitting in the mortar and turning away and then hearing probably the loudest explosion I’ve heard in a confined space to this day. As I turned to look at what was happening I saw a column of flame rising from the mortar but it remained intact.
    Every teacher who was in earshot came running over and I found it quite interesting to not be able to hear anything they were saying as we were all deaf for a few days afterwards. It’s not clear if the NaClO4/Sucrose mixture detonated spontaneously, or if a bunsen burner was left too close to the mortar. The end result was that we were supposed to submit a writeup of experiments we planned to do before being allowed access to the lab again and no big deal was made of the incident as no-one got hurt.
    That was a much more laid back time as I’m sure that if something similar happened today it would make the TV news, involve the bomb squad attending, etc. I’ve never had any need to work with perchlorates subsequently, but have been tempted to mix up a small batch of this material to see if it is shock sensitive or not.

  24. Ryan says:

    I’ve seen a few near misses with perchlorates in my time.
    A former undergraduate minion we had working in our lab was asked to collect together some old samples from a former group member and evaporate them to dryness. 2.5 g later I saw it pumping on the rotovap at 50 deg. C!!!!! Luckilly it didn’t dry out before I realised what he was doing or I wouldn’t have been here to tell the story.
    My former boss used to ask me to batch up multigram quantities of perchlorate salts and dry them on top of the oven! He said it was nice and hot up there, but was unlikely to explode them as he’d never seen it happen. I wasn’t overly keen on being the first to see it happen, so I dried them at room temperature instead – still not particularly safe.
    On another occasion, one of our senior lab personel (who will remain nameless) picked up their perchlorate salt containing round bottom and placed it down on somewhere convenient to go talk to our supervisor. The convenient place happened to be a heating mantle … which was on! 1x VERY loud bang later, he realised something had gone horribly wrong, but couldn’t find where his sample had gone. It vanished! Later, a few shards of glass were discovered in the heating mantle and the penny dropped 😛

  25. simon caron says:

    Not to long ago, when I was in my teen years I asked my teacher that we shoud make mix potassium perchlorate with sulfur in small amount. when I was finish mixing the chemicals, I put the finishing product in the fume hod. the fuse was lit. With in less than second it detenated with a masive shoke wave. Which shook class room. Thank god the fume hod was made of bullet proof glass or I would be seriously injured me.

  26. RICARDO says:


  27. RICARDO says:


  28. Hap says:

    First, it’s PowerPoint fail. Now, it’s comment fail.
    1) You can stop yelling now. If people can’t read your writing in normal capitalization, well, then all caps won’t help (kind of like how yelling at a deaf person won’t make them hear you any better).
    2) “Gay” is an effective epithet only for sixth-graders – thus using it as an insult marks your brain function level in a way you might not have intended.
    3) Spelling (careful) and grammar (paranoid) are always helpful skills for people to take you seriously.
    4) Combinations of organic compounds (not just combustible ones) and perchlorates are probably a bad idea. Perhaps you are just lucky – but luck isn’t a good thing to depend on. See “175 Times, and Then The Catastrophe” for an example.

  29. J-bone says:

    Don’t forget the part of the fail where nobody responded to him for 40 minutes so he re-posted his comment.

  30. Hap says:

    Ignoring him might have been a better option. Oh well, another bell I can’t unring. The only saving grace might have been that he might have kept on going until he got a response, until Dr. Lowe deleted him, or until his mom got home and kicked him off the computer. I don’t know.

  31. Jose says:

    “Wuss” = two eyes, and ten fingers.
    Non-wuss = significantly fewer.

  32. Daryl says:

    Years ago I read something in a chemistry textbook about a compound of chlorine and sulphur and that the guy who discovered it lost three fingers and an eye.
    I laughed out loud at the time, sad, I know but it probably happened around 1850 or so.

  33. qwww says:

    not Cl & S but Cl & N – Pierre Dulong who discovered NCl3

  34. Monster from the Id says:

    “The Frisky Perchlorates” would be a great name for a rock band. ^_^

  35. loupgarous says:
    Is the online version of Dr. John C. Clark’s classic informal history of propellant chemistry, Ignition! He discusses perchlorate chemistry as it was explored by the rocket fuel community in loving (or at least amused and amusing) detail. The perchloryl esters were all considered at one time or another either as oxidizers or monopropellant fuels. And amusingly, pay-for-play chemists were just as determined to ignore the lessons of those who came before them as chemistry hackers (the guys who yearn to make CL-20 in their graduate chem labs) are today.

  36. Jon Barnhart says:

    I use ammonium perchlorate for rocket fuel as a hobby. As with a lot of things it’s much less dangerous when properly mixed with a binding agent and in a solid block. I consider it substantially safer than black powder due to the fact you can light it with a match and not blow yourself up. (Note – PEPCON required heating AP to a high temperature to cause the explosion. It was also granulated, not solid cores like I use.) It’s when its powdered that things turn ugly. What surprises people is how hard the stuff is to ignite in the engine as flameouts happen all too often. The point of this post is that the formulation of these things matters a lot. I also work with magnesium sometimes, but you won’t catch me working with the powdered forms of it.

  37. Jon Barnhart says:

    I use ammonium perchlorate for rocket fuel as a hobby. As with a lot of things it’s much less dangerous when properly mixed with a binding agent and in a solid block. I consider it substantially safer than black powder due to the fact you can light it with a match and not blow yourself up. (Note – PEPCON required heating AP to a high temperature to cause the explosion. It was also granulated, not solid cores like I use.) It’s when its powdered that things turn ugly. What surprises people is how hard the stuff is to ignite in the engine as flameouts happen all too often. The point of this post is that the formulation of these things matters a lot. I also work with magnesium sometimes, but you won’t catch me working with the powdered forms of it.

  38. Chris searle says:

    As a young chemist/entomologist, I came across a reference to a formulation known as ‘Goffes reagent’ used for restoring the colour banding to dead horseflies eyes for identification purposes ( yes, I know). It required mercuric perchlorate. The lab didn’t have any so I thought I’d boil up some mercury with 70% perchloric acid. To my credit I did do it on a sand bath in a fume cabinet. All seemed well and I went for lunch, on arriving back in the lab people seemed to be rather excited and I noticed that my fume cabinet appeared to have been painted orange-red from the inside……

  39. David Edwards says:

    Those familiar with the PEPCON incident will enjoy this.
    Back in the 1970s, a toy company called Thomas Salter, here in the UK, used to make chemistry sets. One of the reagents they supplied therein was potassium perchlorate. If I can find it in the attic, I’ll dig out the manual for one of these chemistry sets, and introduce you to things that would have Health & Safety not so much filling their underpants, rather going into full-bore prolapse mode. 🙂

  40. Stu says:

    I spent a year using perchlorate salts in electrochemical experiments. During that year my thyroid gland up and quit on me. My hindsight research turned up concerns about perchlorate effects on thyroid functioning; has anyone else experienced this rather less dramatic but maybe more consequential effect of perchlorate use? That was 20 years ago and i still take thyroid hormone replacements.

  41. Stoneshop says:

    ” Those rocket guys leave few stones unturned.”
    Stones, rocks, and entire concrete bunkers have been flipped over in the search for the ideal rocket fuel.

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