Chisholm
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Anhydrous HNO3 from DCM and dry ice
I'm trying to generate about 40mL of anhydrous nitric acid.
Mixing 53 mL azeotropic HNO3 and 48 mL of 98% H2SO4, then extracting with 100mL of dichloromethane produces an organic layer containing about 15 grams
of anhydrous HNO3.
I can't distill off the DCM, because I don't have a vacuum setup and warming the solution would decompose some of the nitric acid.
Can anyone tell me anything about the alternative method of using dry ice to freeze out the nitric acid?
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Chisholm
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Nobody?
[Edited on 5-3-2017 by Chisholm]
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Sulaiman
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DCM will evaporate quite quickly at room temperature
or slowly at 0oC !
https://en.wikipedia.org/wiki/Dichloromethane_(data_page)
https://upload.wikimedia.org/wikipedia/commons/f/f8/LogMethy...
EDIT: I don't know how quickly the anhydrus HNO3 absorbs H2O and CO2 from the atmosphere though.
[Edited on 3-5-2017 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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Dr.Bob
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This just sounds like a dangerous prep that requires some experience and proper equipment to safely do, which is not very common, so no one wants to
give you bad advice that might lead to your injury. I would guess that "anhydrous nitric acid" might well explode upon contact with nearly anything
organic, including DCM. There are numerous web sites that describe the synthesis and properties along with information on the hazards and issues, I
would try Googling it and look at some.
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Chisholm
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Quote: Originally posted by Dr.Bob  | | This just sounds like a dangerous prep that requires some experience and proper equipment to safely do, which is not very common, so no one wants to
give you bad advice that might lead to your injury. I would guess that "anhydrous nitric acid" might well explode upon contact with nearly anything
organic, including DCM. There are numerous web sites that describe the synthesis and properties along with information on the hazards and issues, I
would try Googling it and look at some. |
According to the patent for the process, the DCM extract won't hold more than ~15 grams of HNO3 per 100ml DCM; there's not enough oxygen to start
anything unless you did something stupid like set it on fire. I've boiled off DCM from these extracts to get HNO3 before without incident; however the
product is still yellow and I'm still out a quantity of a hard-to-find reagent. Plus, DCM fumes are quite unpleasant; a method that relied on cold
rather than heat would be easier on the ducts.
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phlogiston
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Your answer suggests that you are not aware that HNO3, being a strong oxidiser itself, can react violently with organic materials even in the absence
of oxygen. Moreover, mixtures of concentrated anhydrous HNO3 and organic materials are often hypergolic (ie. they spontaneously self-ignite).
I have never tried the method you describe, but please make sure you know what you are doing. This could potentially be very hazardous.
[Edited on 4-5-2017 by phlogiston]
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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Elemental Phosphorus
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If you have a distillation apparatus but no vacuum pump, simply distill the fuming nitric acid at room temperature. Decomposition is an issue at
atmospheric pressure distillation, but not that much of one. If you have no distillation apparatus, it will be hard to get fuming nitric acid. The
problem with boiling DCM and fuming nitric acid is that partially chlorinated organics tend to produce phosgene when oxidized, and while a ruaway
oxidation seems unlikely, that would be very bad. Champlayer made a video on the mononitration of toluene using nitric acid in DCM, but he didn't boil
the DCM, he let it evaporate. Using this as a way to produce nitric acid would be very wasteful of DCM, and honestly I think you'd be better off
buying a distillation apparatus. You can find complete ones from China for 40 dollars. Distilling concentrated sulfuric acid and an anhydrous nitrate
salt will give you about 98+ percent nitric acid, especially if you use an excess of sulfuric acid. As for the freezing out method, I have no idea.
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chemplayer...
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Be careful - the reports we read were that the DCM and nitric acid mixture above a certain (fairly low) concentration could detonate. Definitely
wouldn't want to distill this mixture, and would recommend mixing any reaction mixture with a lot of water before working up (and evaporating off the
DCM) in order to get rid of any residual nitric acid in the solvent.
Also consider that nitric acid even at low temperatures is fairly volatile. On distilling or evaporating off the DCM under reduced pressure you will
inevitably end up with a mixture of DCM and nitric acid vapour, which doesn't sound like a combination...
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Eyeborg
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Chisholm, in my opinion, if you wanted to get anhydrous nitric acid, it would be much easier to react the azeotropic nitric acid with a base, like
sodium bicarbonate, then react the sodium bicarbonate with concentrated sulfuric acid to get nitric acid. No need for DCM and dry ice.
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Melgar
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There would be no need to mess around with sodium bicarbonate, since that's an effective way to get anhydrous nitric acid all by itself. You have to
distill the nitric acid off afterwards in either case. You could try "El Cheapo" nitric acid distillation, and get a glass or aluminum pot (aluminum
is, surprisingly, the best choice of metal here, although glass is better because you can see through it) then put a goblet in the middle of it. Pour
your 68% nitric acid in the pot, along with whatever desiccant you plan to use (note that if your desiccant is sulfuric acid, you obviously cannot use
an aluminum vessel), then secure a layer of thick polyethylene to the top of the pot, such that it droops down in the center, and the lowest point is
directly above the goblet. Then fill the polyethylene with ice and pour whatever cheap chloride salt you have on the ice. Put the heat on, and the
vapors will collect on the cold plastic and drip down into the goblet. The only tricky part here is that you have to maintain a collection rate
that's fast enough that that it will keep the nitric acid in the goblet significantly colder than the nitric acid in the bottom of the pot. However,
it does work quite well if the goal is just a small quantity of fuming nitric acid. This works especially well if you have a beaker large enough to
hold a goblet with room at the top for the polyethylene and ice. However, it can work with a large pickle jar as well.
[Edited on 5/7/17 by Melgar]
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