jackchem2001
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Isopropyl nitrite synthesis explosion (warning)
I have split this thread into two parts since the causes of the explosion are probably not relevant to many people.
Causes of the explosion
A while ago I had a large glassware explosion occur when adding isopropyl alcohol to sulfuric acid and potassium nitrate. This reaction nominally
gives isopropyl nitrite and acetone. The explosion occurred in the condensor (which did not have cooling water flowing through it yet) and left the
distillation head, addition funnel, and boiling flask unharmed (but several smaller pieces of glassware were destroyed). Shrapnel was sprayed
everywhere. A moderately sized fire occurred on the surface of the aluminium foil insulation you can see in the back of the picture (presumably
isopropyl alcohol that was in the addition funnel) but it burnt itself out quickly without damage.
The apparatus was not very well designed and at the time I believed the explosion to be due to insufficient pressure release as opposed to a chemical
explosion. Today I decided to recreate the apparatus at the time of the explosion to see if that is true.
The hose inlet leads to an air pump which gives 10% atm gauge pressure. On the day of the real experiment, all joints connected to the boiler were
clamped with metal clamps (not shown in the picture). The only unclamped stoppers were in the receiving flask and on top of the addition funnel. My
goal with this recreation was to test whether the liquid in the addition funnel sidearm (as was present at the time of the explosion) prevented the
stopper at the top of the addition funnel acting as a pressure release. As expected, it did not and the stopper at the top of the funnel popped open
once I closed the test system to the atmosphere and turned on the air pump (to simulate pressure buildup).
To me this means the explosion was not a pressure explosion (as it would have been released) but instead a chemical one. A lot of NO2 is produced in
the reaction and it also gets hot (the nitrite ester is distilled off without heat provided). My guess is that the gas in the condensor spontaneously
detonated but I have no idea why that would occur in the condensor and not the boiling flask. In any case, the apparatus was still poorly designed and
I now always have pressure release connected directly to the reaction vessel.
What it was like at the time
To make this thread a bit more relevant to others I will describe what it was like on the day. I went to reach for my hose to turn on condensor water.
At one moment there was an entire distillation setup. At the next moment, it was gone. I don't recall hearing an explosion, just a ringing in my right
ear which subsided in a couple of seconds. In this state you don't really think and instead act decisively. I think your memory is also a bit impaired
so I've written as best as I can remember.
Immediately after, I noticed the fire and the ape brain thought that came to me was literally "fire, okay, water" (without even considering if it was
the aluminium foil burning, which was where the fire was). But first I grabbed the reactor (which was absolutely pouring out NO2) and ran through my
house and threw it outside. By the time I came back the fire was gone. I then noticed I was bleeding on my wrist. I ran to the sink and flushed it
out. I noticed that there was basically no pain. Fearing that I was cut/had acid on other parts of my body without knowing it, I ran back to my room
and phoned for an ambulance (which is a pretty stupid fear in hindsight, but whatever).
I realised that an ambulance was pretty excessive mid call but the operator said if you don't need it you can say no (or something like that, I don't
remember). At this point I noticed that my room absolutely reeked of NO2 and it wasn't good to stay there. The rest of the day is not especially
interesting. Cleanup was long and tedious. My main point would be that if a serious accident ever occurs, you won't really think clearly so you need
to have done the thinking beforehand.
Summary
The short version is don't carry out this procedure. I left a post in another thread about it before this accident. If this could be edited to have a
warning and link to this thread that would be good  https://www.sciencemadness.org/whisper/viewthread.php?tid=16...
I did not take any pictures of the incident as this is not a 'cool story' to brag about but a serious incident. Considering my proximity to the
explosion (maybe 0.5m) and the amount of power/shrapnel I am extremely lucky to be left without permanent harm.
[Edited on 13-12-2024 by jackchem2001]
Edit by Texium: fixed link to split/moved thread
[Edited on 12-15-2024 by Texium]
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Sir_Gawain
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Potassium nitrate? Not nitrite? Isopropyl alcohol undergoes runaway nitration when mixed with nitric acid.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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jackchem2001
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Yes, nitrate. I made this post about this reaction: https://www.sciencemadness.org/whisper/viewthread.php?tid=52...
I have done it in a controlled way before. I am reasonably sure it produces the nitrite ester but I will not repeat the experiment. The mechanism
requires NO2+ as in a nitration mixture (NO2+ -> isopropyl nitrate -> elimination of adjacent hydrogen with loss of nitrous acid -> volatile
nitrite ester).
The runaway nitration comment is very interesting to me and it seems like a good candidate for the root cause of the explosion. As best as I can
remember, the isopropyl alcohol was added in small portions through the addition funnel as I was not collecting distillate and wanted the heat of
reaction to carry the product over (as I had done in previous runs). Large amounts of NO2 were formed but I did not believe this to be a problem as
the apparatus would have blown out a stopper to relieve the pressure (though I have since improved this safety mechanism in recent experiments).
Previous runs also evolved a fair amount of NO2 without incident.
Note that the sulfuric acid/KNO3 mixture is quite solid and does not stir. The reaction also requires a minimum concentration of acid to proceed, so
perhaps this combination lead to a buildup of unreacted isopropyl alcohol which eventually reacted all at once. I still don't know why this would lead
to a chemical explosion in the condensor and not the boiling flask. The position of the explosion is what lead me to originally believe it was a
pressure explosion but the test performed shows that is very unlikely as the unclamped stopper of the addition funnel (even with the side arm slightly
clogged with liquid as in the picture) relieves the pressure.
[Edited on 13-12-2024 by jackchem2001]
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Sulaiman
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Very glad that no real harm was done
I'm not familiar with the reaction so I won't comment on that,
but it was a good reminder of how quickly things can go bad.
I doubt that any home experimental chemist can ever be fully prepared
as we each delve into our own unknown territories.
PS. there is a clue in the name of this site. 
For context:
Every physical hobby that I've had carries it's own physical hazards
Human evolution and society are due to risk takers.
I hope that this forum will always be available for a little 'madness'
(If 'mad' = 'not normal' then please show me a 'normal' person, I'm 70 and don't recall meeting one yet)
[Edited on 13-12-2024 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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Fery
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I understand. You used nitrate and excess of alcohol to produce nitrite in situ. Nitrate is much better available than nitrite.
Glad that you are OK and also most of the glass.
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jackchem2001
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Thanks for your comments. I didn't mean this thread as some weird hugbox/scaremongering thing, just as a warning about this specific procedure. And
also a reminder to think about safety before an accident since during one you might not be thinking clearly.
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Sulaiman
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Well in that case,
What a dumb-ass thing to do!
Boiling volatile flammable solvents indoors,
Not smart.
In a nitration mix...even less smart
Without researching all possible reactions and side-reactions,
and their hazards,
With inadequate planning, accident prevention and remedial options in place...you should know better.
Are you some kind of mad scientist ?
I've imagined you running through the house with a runaway reaction in a flask that is belching out toxic brown clouds,
...while escaping the fire behind you.
D'oh !
It's tales like this that cause chemophobia.
Go sit in a corner and think about what you've done,
and what could have happened
you naughty boy.
Happy now. ? 
CAUTION : Hobby Chemist, not Professional or even Amateur
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bnull
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Quote: Originally posted by jackchem2001  | | A while ago I had a large glassware explosion occur when adding isopropyl alcohol to sulfuric acid and potassium nitrate. This reaction nominally
gives isopropyl nitrite and acetone. |
Correct me if I'm wrong. You used a nitrating mixture in a reaction where one of the products is acetone. Bretherick's 7th Edition, page 490: "Acetone
will be oxidised with explosive violence if brought into contact with the mixed (nitrating) acids, particularly under confinement." This would be an
"I'm not going to do this" point for me.
| Quote: | | But first I grabbed the reactor (which was absolutely pouring out NO2) and ran through my house and threw it outside. |
 You don't have a fume hood, or at least a window nearby? Jesus...
When you see that a "lot of NO2 is produced in the reaction", it's time to reevaluate the procedure. The bloody thing is still toxic even if see no
brown fumes.
| Quote: | | Note that the sulfuric acid/KNO3 mixture is quite solid and does not stir. |
This is another "I'm not going to do this" point.
I suggest you buy two books: Brethericke's Handbook of Reactive Chemical Hazards and Safety in the Chemical Lab by Pieters. Physical copies, so they
can sit there in your lab. Read Pieters from cover to cover. Read the relevant entries of Brethericke's every time you want to try a
new reaction. Bretherick's is over 2500 pages, with references almost everywhere, covering practically every reagent you will ever use.
I'll add your mishap as a note in Bretherick's, under 2- propanol.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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jackchem2001
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In regards to a fume hood, whenever I work with NO2 (which is not often) I never smell it even though it has a low odor threshold. My ventilation is
fair and I can handle it being released from the apparatus in small amounts. Even a lot being produced is completely fine provided it stays in the
apparatus (scrubbers deal with it well). It is easy in hindsight to say that I should have reached for my fire extinguisher first before dealing with
the reaction mixture but I just had a distillation apparatus turn into shrapnel right in front of me. Obviously I was not thinking totally clearly and
this is part of the reason I made this thread. It does make me look like a fool but I don't care if it is useful to others.
Anways, in regards to the chemistry, I remember before first doing this procedure I did do research into isopropyl nitrite/nitrate and nitroform (from
enol chemistry of acetone). I did not get the impression that these materials were especially sensitive and did many test tube scale runs to test the
reaction. However, I admit that I completely missed the explosive potential and that is on me. Thank you for the books you have mentioned.
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digga
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It seems to me that chemistry is like an iceberg. The actual experiments are the parts you see. The research into what you are trying to do is the
rest. It will reveal the pitfalls and dangers. It will show you all the products, desired or not. It will show the reactions of the products and
the side products. It will save you much misery and pain.
Working chemists have better tools. The can use a GC to analyze the products. They have fume hoods, showers to protect them from the products.
We mostly do not have these things. So be careful. It cuts down on the WTF moments.
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Texium
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I second bnull and digga’s posts. The violent reaction of nitric acid with acetone is widely known, and if you had done your due diligence before
attempting this even on a test tube scale, you would have known it was a bad idea. It’s a shame that nobody pointed that out in the thread you
posted your procedure in, but it seems like it got buried and mostly ignored (I’ll be dealing with that soon).
Furthermore, scaling directly from test tube scale to what appears to be a 1 L flask is terrible practice for any reaction, but especially so for a
reaction where the potential for runaway is high and large volumes of gases are produced.
[Edited on 12-15-2024 by Texium]
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