Hands on experience with DCM method

[vulture]

Recently I've been trying to extract HNO3 using DCM, as mentioned in US patent 3,981,975.

Materials used:
96% H2SO4 technical grade
70% HNO3 technical grade
DCM, technical grade, no information about contaminants
(all OTC material)

I added about 50ml DCM and 30ml HNO3 to my separatory funnel. After that 20ml of H2SO4 were added SLOWLY, as the hydratation energy caused a significant amount of DCM to evaporate, leading to potentially dangerous overpressure.

After vigirous shaking and frequent venting I let the 2 layers separate for a few hours.

The first interesting fact was that the NOx which were present in my yellow HNO3 did not dissolve in the DCM phase, which was now totally clear and colorless.

I drained some 5ml of extract for testing.

The extract started fuming copiously after some time, presumably because most of the DCM had evaporated. Spills which were cleaned up with paper immediatly nitrated the paper, again releasing large amounts of HNO3 vapor.
Also, after prolonged exposure to air, it seemed to attract fair amounts of water.

When I tried using the DCM/HNO3 mixture "as is" in a nitrating mix, I observed that sulfuric acid was mixable with the extract. However, as soon as trace amounts of water are present, the H2SO4 will only dissolve in the aquous phase, possibly because of it's hygroscopic behaviour.

On a side note, I'd like to point out that H2SO4 is still needed for most nitrations, since it does not only dehydratate, but also makes the formation of the necessary NO2+ ion possible:

2H₂SO₄ + HNO₃ ---> H₃O⁺ + NO₂⁺ + 2HSO₄^-

Nitration of cellulose was only partially succesful, but the cellulose was of unknown quality.
A larger batch experienced a horrible runaway.

I left the separatory funnel and it's contents standing for 2 days and when I returned to try an RDX synth (no H2SO4 needed here) a bad surprise was awaiting me.

For some mysterious reason, the DCM/HNO3 and H2SO4/H2O layers mixed! :confused:
Upon careful examination I found out that my PTFE grease (used to lubricate the valve) had become a distinct yellow, but I don't know if it's the one to take the blame here.

Further testing is to be conducted in the future....

I'd like to hear comments/ideas/personal experiences, as this method does seem to be able to produce highly concentrated HNO3 without dissolved NOx.

EDIT: hexamine seems to be slightly soluble in DCM. This should be a good thing for RDX synthesis, because if the 2 reagents are dissolved in DCM, they can't come into contact with H₂O. Furthermore, the DCM will separate any formed H₂O, shifting equilibrium to the right. Atleast that's my theory...

[zeocrash]

where do you get your DCM from, in the UK the only source i've seen is as paint stripper, and the main impurity in this is methanol, this could explain the mixing of the layers.
correct me if i'm talking out my ass but i bleive methanol is miscable with both water and DCM, which could explain some of the mixture mixing

[nbk2000]

The one time I tried it, I used a dry ice/acetone slush to freeze out the NA as crystals. They immediately liquified once I removed the container from the cooling bath, so I wasn't able to filter them out, though I suppose you could use a fine metal mesh like that used for tea filtering and had it cooled in the the acid mixed, you could scoop them out and dump them into something else before they melted.

Or you could distill off the DCM which would leave the NA behind.

Where'd you get your DCM from? Is it a paint stripper or an industrial solvent?

FYI, water is slightly soluble in DCM, though something less than 1%, and DCM is soluble in water at (IIRC) 4%.

I posted about this method elsewhere on here.

[vulture]

I'm not exactly sure about the purity, it comes in an unmarked container. My guess is it comes from bulk industrial stock, I buy it OTC at a shop where I can get all kinds of technical grade chems.

I doubt it was methanol contamination that caused the layers to mix. They only became miscible after 3 days or so.

[zeocrash]

Hmm wouldn't distilation produce some decomposition to NOx.
would it be possible to remove the DCM by bubbling dry air through the acid DCM mix. causing the DCM to evaporate off.

[mongo blongo]

The boiling point of DCM is well below the decomposition temp of HNO3, that's the advantage. :)