Org Prep Daily

August 2, 2012

Shake and pray

Filed under: lab destruction, procedures — milkshake @ 6:16 pm

There is a pop-chem procedure on YouTube that I find astonishing – it beats the Diet Coke and Mentos trick hands down:

A guy loads NaOH dry solid pellets, about 1 inch high, into a plastic bottle, and adds about 2-3 inch thick layer of dry ammonium nitrate granules. Then he fills the bottle with ethyl ether and adds a good chunk of lithium metal foil. He screws the cap on and swirls the mix around. God have mercy.

This man is not building a home-made ANFO for roadside bombing. It is not going to be a Molotov cocktail enhanced with a metal/oxidizer, or perhaps a crude rocket. He is making a batch of meth by the Shake and Bake method. As he ads a pack of ground pseudoephedrine pills, he squirts in a small amount of water, caps the bottle and starts shaking real fast. The water initiates a vigorous and pretty much uncontrollable reaction of the lithium metal with ammonium nitrate. The solids in ether gradually liquify and become a bottom layer sludge – this all is accompanied by evolution of  copious amounts of ammonia and hydrogen. So he shakes this thing by hand and he periodically vents the ammonia by loosening the cap  when the plastic bottle bulges up too much. Eventually the reaction slows down, the majority of lithium metal gets dissolved and the leftover lithium pieces floating on top of ether attain a bronze/copper hue, this marks the completion of the reduction. The ether layer is decanted into a small plastic bag, saturated with HCl gas (evolved from another soda bottle with sulfuric acid and NaCl) and the hydrochloride salt crashes out and is collected on coffee filter and dried. The yield is about 1-2 grams of a hilbilly-grade crank in form of a white powder, from one large pack of pseudoephedrine pills, about 2 hours start to finish. No glassware anywhere.

The method does not scale – attempts at running bigger batches end in self-immolation. A common error is adding too much water at the beginning, which leads to uncontrollable takeoff:  the whole ether/ammonia/NaOH/NH4NO3/Li brew squirts out. One can try and keep the lid on an a bulging soda bottle by a sheer force but as the Li metal floats on top and fast reaction makes the chunks of lithium pretty hot,  they tend to burrow through the plastic wall and an impressive stream of flaming goodness rushes out with them, delivering bright red and yellow-colored ether flames accelerated by ammonium nitrate and lithium metal all over the place. As one skin graft patient observed “I haven’t seen stuff burning this fast before”.

The Shake and Bake meth is a twist on the classic method using Li metal with anhydrous liquid ammonia/ether. The outdoor storage ammonia tanks are now getting watched and additives are introduced into agriculture-grade NH3(l) so as to ruin its usefulness for dissolved metal reduction. Hence the soda bottle modification for ammonia generation in situ. No need to go to fields, now you can cook in the safety of your home…

Note: It would be easy for a manufacturer to add some organic soluble iron compound like Fe(acac)3 or ferrocene to the ether-based starter fluid  and likewise a small pinch of FeSO4 to the ammonium nitrate in cold packs and lye/drain opener. A finely divided iron promptly decomposes Li metal solution in ammonia to lithium amide and so it would make these materials useless for home brewing.

January 30, 2012

Potassium hydride self-ignition

Filed under: lab destruction — milkshake @ 1:40 pm

I had a rather bad fire last Friday. I was washing a large jacketed glass reaction vessel used for polymer scale-ups, after pouring the reaction mixture out, and a tiny particle of potassium hydride (from this poorly quenched reaction) that was adhering to the bottom of the reaction flask ignited just as I was giving the flask a proper acetone rinse. So I had a flaming flask in my hands + burning hands + flaming sink in front + a whole bunch of wash bottles ablaze next to me (plastic wash bottles peeing their burning solvents around…) A colleague promptly put the fire out with a mid-sized CO2 fire extinguisher before the flames spread any further. There was no damage to the lab, my fingers or the reaction mixture but it was a pretty scary situation – considering how fires in organic labs can get out of control so fast.

Potassium hydride pyrophoric nature is well documented in the literature; from my limited experience I would say KH is quite comparable to potassium metal in its tendency to flame up. But there are some aspects that make KH more treacherous than K metal: KH in paraffin or mineral oil is docile and only when the oil or wax is washed off the pyrophoric nature becomes apparent. Also, the KH appearance (a grayish-white powder) is less dramatic than shiny low-melting globules of K metal and one cannot easily guess whether KH is fully consumed or quenched by the sediment appearance if the reaction produces inorganic precipitate of its own. Also, I noticed that some alcohols react with KH in THF surprisingly sluggishly while reaction of other alcohols is prompt – I believe the solubility of the K-alkoxide in THF plays a role and the KH particles may get coated by a poorly soluble material and laze about the bottom – and then at some later point flame up when least expected.

Since K-alkoxides have significant reactivity advantages over Na and Li alkoxides in alkylation reactions[2], and since the easy-to-handle KH formulation in paraffin wax is now commercially available, it is likely that KH will get used increasingly more often in place of NaH. Despite its innocuous appearance KH is less tame than NaH;  having unreacted KH excess present in the reaction mix makes it prone to auto-ignition during the workup if the reaction was not quenched with care.

Note 1: I was impressed how good is CO2 extinguisher for large solvent fires – and it leaves no mess behind. I don’t think a dry powder extinguisher would have worked nearly as well.

Note 2: Taber et. al.: Tet. Letters 51 (2010), 3545-6

July 26, 2011

Expanding liquids break closed vessels

Filed under: lab destruction — milkshake @ 2:05 pm

I had a dumb mishap today: A 100mL Schlenk storage flask with 1,5-cyclooctadiene shattered. When I distilled my COD by vacuum transfer this morning I filled the storage flask all the way to the top and then turned the teflon stopcock shut. There was no head space left in the flask; as the liquid warmed from about 10C up to room temperature it expanded enough to burst the glass.

Coincidentally, my colleague finished off a 20L jacketed glass reactor in a similar manner just yesterday – he was cleaning it after the experiment and the heating jacket was shut off, both the inlet and outlet valves were closed while the jacket was still filled with polysiloxane heat transfer fluid. When the reactor was rinsed with ambient water it suddenly shattered: a small temperature difference was apparently enough to cause the silicone fluid expansion in the jacket and there was no air bubble space nor a tubing attachment whereto the silicone liquid could expand. Looking back, this jacket over-pressurizing would not have happened if one of the valves was left open.

I suppose we proved that liquids are incompressible and expand with heat.

Link: The Great Boston Molasses Disaster

August 11, 2009

Dear ACS journal editors – please return from your vacation soon

Filed under: lab destruction, lit highlights — milkshake @ 1:14 am

dovolena credit: National Geographic ‘Photo of the day’

The spectacular “NaH catalytic” oxidation recently published in JACS has been thoroughly covered elsewhere. I would like to bring your attention to another jaw-dropping paper that just came out in Org Letters:

http://pubs.acs.org/doi/abs/10.1021/ol901250c

Acetophenones and 1-aryl-ethanols are oxidized to benzamides by heating the material with 3 – 4 equivs of iodine and ammonia in a pressure vessel. There is only a passing reference and footnote that “nitrogen triodide might form in the mix.”

In fact, NI3.NH3 readily precipitates upon mixing iodine with aqueous ammonia. (The products vary; a gradual iodine addition to a large excess of ammonia yields ammonium iodide and nitrogen.) Nitrogen triodide is a notoriously super-sensitive primary explosive. I spent some time hospitalized in eye clinic when I was ten years old – my corneas got burned with iodine and my eardrums ruptured because of playing with a spoonful of nitrogen triodide. (The window pane flew out and I was thrown to the ground by the blast;  it took me half a year to fully recover and this all was from few grams of dry material going poof, unconstrained). I cannot warn strongly enough against mixing iodine with ammonia in a pressure flask and then heating the stuff up!

The authors run these experiments on a 1 mmol scale and they give no details about the order of addition. Since the transformation is pretty useful – with a good substrate scope and it looks simple enough (its done in water) –  sooner or later some innocent person is bound to mix up a big batch in the wrong way – and as he screws on the the pressure vessel cap he is gonna blow himself up into a mauve cloud

November 25, 2008

More lab disasters 2

Filed under: lab destruction — milkshake @ 6:06 pm

When I was in high school, I got free run in a chemistry lab that belonged to a youth center. I was trying to synthesize papaverine, and this was completely above my ability (and the lab resources) but I was very persistent. The key building blocks for papaverine are homoveratric acid and homoveratryl amine, and I set out to make them by myself: I had several bottles of catechol to start from - my problem was how to methylate it, I could not just buy stuff – I had to go by with what was in the stockroom.

First I made lots of methyl iodide, from red P + iodine and methanol – refluxing and distilling it on the bench so I know how methyl iodide smells - but the methylation was messy. Next I tried to make dimethyl sulfate from sulfuryl chloride and methoxide in situ, and it worked to some degree – the vanilla smell of guaiacol was everywhere – but again I could not isolate anything from the mess. So my next idea was to use diazomethane made from nitrosomethyl urea.

So I was cooking and then distilling AcNH2 on a grand scale, from AcOH and urea - and this went quite well (apart from the all-pervasive mice urine-like smell of acetamide) and then I was to carry out the Hoffman degradation.  When one uses concentrated aq KOH and bromine, the in-situ generated MeNCO reacts with a second molecule of acetamide to produce MeNHCONHAc, an intermediate for preparing nitroso methylurea; I needed it for a large-scale diazomethane reaction so I did it on a mol scale on the first run.

The procedure called for Br2 to be added into AcNH2 + 30% aq KOH mix in a 1L flask, then gently heating the mix until a rapid gas evolution commenced. Since I scaled up the preparation by a factor of twenty on the first run, and I did not have a 20L flask, I used the biggest flask I could find, a 4L Erlenmeyer, and loaded the stuff up; it all fit in there. But then, the mix did not wait to be gently heated and instead jumped out at me all at once.

I usually did my work without glasses, on the bench - but this one time I put goggles on and it was well worth it. The hot KOH + KOBr solution rained all over the place and bleached my hair blond; also my T-shirt and jeans ended up with white vertical stripes. A colleague stood nearby and saw the whole thing and dragged me into shower.

Eventually I did make some nitrosomethyl urea and diazomethane but never finished the papaverine project. No explosion, poisoning or other injuriy happened during all these crazy experiments. But there was another like-minded highschool kid, repeatedly working on some chemistry involving acetone cyanohydrine, and he was making it from acetone and NaCN, in our little fume hood with a lousy fan-driven exhaust. I think he never finished his project either but I remember once we were going down the stairway and he was saying “I don’t know if this exhaust really works ’cause I was smelling hydrogen cyanide this time a lot” and then we got outside there were two dead pigeons on the grass and we looked up and the exhaust from our fume hood was looming right above us…

November 13, 2008

More lab disasters

Filed under: lab destruction — milkshake @ 3:41 am

Ψ*Ψ has a new post on undergrad lab disasters, I would like to add few more of my own making, from two decades ago:

In the junk-room of our chemistry department I found an ancient belt-driven vacuum pump that operated on 380V three-phase AC. I brought it from the basement into our freshly-renovated lab, put it on the bench, plugged it in to see if it worked – and it did. Unfortunately the 380V AC wiring must have been wrong in our lab (we never used 380V plug in there before) or the phase order in the pump itself was switched. At any rate, the motor started spinning backward and the pump pumped out its oil from the inlet hole at once -  a gallon of black muck that hasn’t been changed for eons. The intlet had a short piece of rubber hose on and it worked like a nozzle - directing the stream of goodness at the high ceiling, right in the middle of the room whence it rained down all over the place. This mishap actually shut down our lab for two weeks as the oil-soaked plaster had to be knocked off down to the brick and concrete in order to make the new plaster stick.

Some months later I was working as a guest student in another lab (in another building, at another school) – and they had a gas-powered water heaters installed above the sinks because their building lacked central hot water. It was a strange and dangerous thing to have in the lab (right next to the  organic solvent bottles); and the last person in the lab always made sure to turn off the pilot lights before leaving.  One early morning I was washing my hands and water was coming out freezing cold - the  pilot light was off -  so I grabbed matches and without turning off the running water (and the stream of gas), l lit the pilot.  A yellow fireball shot up and the casing flew off from the heater infront of me, with an impressive bang. When my ears stopped ringing  I could hear a calm voice from the opposite corner of the lab where a colleague sat at her desk: “Mr. Borivoj, I promise that the next time I’ll pour my coffee over you.”

The same colleague a week later decided to clean up and inventorize all her glassware - she emptied her drawers and put it all on a long bench. Meanwhile I was distilling 0.5L of old and nasty-looking  N-methylmorpholine to which I added lots of calcium hydride - and when I finished I had CaH2-rich leftover sludge in the distillation flask. I was asking around if it was OK to quench it with ethanol (I had quenched NaH and BuLi before) and a faculty dude said I should go right ahead; I did not realize they probably did not work much with CaH2 in that lab.  So I was carefully adding ethanol with cooling, the bubbles were coming out, calm and nice.  One hour later (back from lunch) I added some more ethanol - no bubbling anymore – so I was certain I could pour that into the waste, and I went to the sink to dilute the sludge with water a bit so that I could pour it out. Suddenly it became clear that ethanol does not really quench CaH2, and water does. The  mud volcano in my hands erupted away, spewing the hot lime and fishy amine on the nearest bench - all over that clean and inventoried glassware. The owner again took it  calmly - she just muttered “We have to assign you a working space in the hallway”…

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