Sciencemadness Discussion Board

Anhydrous HNO3 from DCM and dry ice

Chisholm - 23-4-2017 at 04:15

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?

Chisholm - 3-5-2017 at 09:52

Nobody?


[Edited on 5-3-2017 by Chisholm]

Sulaiman - 3-5-2017 at 10:04

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]

Dr.Bob - 3-5-2017 at 11:02

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.

Chisholm - 3-5-2017 at 18:37

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.

phlogiston - 4-5-2017 at 02:26

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]

Elemental Phosphorus - 4-5-2017 at 04:37

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.

chemplayer... - 4-5-2017 at 06:18

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...

Eyeborg - 6-5-2017 at 08:47

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.

Melgar - 7-5-2017 at 02:16

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]