alking
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Handling possible nitrogen trichloride/dichloramine contaminated DCM
I found a bottle of dichloromethane I set aside to later recover which is contaminated with ammonia. It has been sitting for a number of months,
likely less than a year, but I can't say for sure how long. I'm concerned some nitrogen trichloride has formed in it and I don't want to mess with it
until I can be assured I can do so safely. I have not opened it even as I'm not sure just how sensitive it may be.
Now I know I need to neutralize it with a mineral acid, but what is the safest way to go about doing so? Is there a risk from simply opening it?
Should I dilute it with water to minimize any combustion risks before introducing the acid? Should I drop the temperature before doing anything to
lower its reactivity? Am I just being paranoid and there's no danger at all? There are some kind of solids in the bottle clumped in the bottom, but
that's probably some trash as I really don't know what was in the DCM:NH3 other than it was likely some type of extraction and thus other junk can be
expected to be present anyway.
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Sigmatropic
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Unless chlorine or other oxidizing agents were used chloramines are not to be expected. Partial ammonolysis of dcm yields formaldehyde and/or
hexamine. But I must admit I have no sources for this. If one wants te be sure treat it with reducing agents such as those used to destroy peroxides
in ethers, Wikipedia mentions Mn(II), Fe(II) or PPh3. My bet would be on a bisulfite wash. http://pubs.acs.org/doi/abs/10.1021/ie50654a005?journalCode=...
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alking
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Well that sounds much safer/little to worry about then. Whatever might have formed, if anything, I need to process it if only to recover my reagent
bottle, I just want to make sure I'm not doing anything dangerous in the process. I do value my fingers and all.
I do not normally leave bottles of unrecovered solvent or post rxn mixtures sitting for extended periods of time to have to worry about such things,
but this one snuck past me. I'll wait to make sure others agree and if so I'll go ahead and work it up as suggested. Thanks.
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JJay
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It could contain some amount of phosgene. Definitely make sure you have good ventilation.
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Sigmatropic
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Phosgene can be present in unstabilized chloroform, I've heard of no such reports with DCM. A quick search yields some 1960 reports about gas burners
used in an atmosphere high in Dcm producing symptoms similar to phosgene poisoning. It seems this is irrelevant in the case of storing DCM containing
NH3. Nonetheless adequate ventilation should be used when handling DCM, and any other volatile organic compound for that matter.
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Melgar
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I've wondered before if chloroform and ammonia react under any conditions to give HCl and HCN. Seems unlikely, but possible.
In this case, if they did react, it'd probably just go to chloromethylammonium chloride, then fall out because amine salts aren't soluble in DCM.
Formaldehyde could form if a molecule of DCM reacted twice with an ammonia molecule, forming the imine, which water could then hydrolyze. I don't see
how phosgene could form though, other than free-radical reactions like it catching fire.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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JJay
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Quote: Originally posted by Sigmatropic  | | Phosgene can be present in unstabilized chloroform, I've heard of no such reports with DCM. A quick search yields some 1960 reports about gas burners
used in an atmosphere high in Dcm producing symptoms similar to phosgene poisoning. It seems this is irrelevant in the case of storing DCM containing
NH3. |
DCM from chemical suppliers is usually stabilized with amylene or a short chain alcohol to prevent phosgene from slowly forming in it (see here: http://www.sciencemadness.org/talk/viewthread.php?tid=5294). It can react with air to form phosgene on contact with light or metal. It's usually
safe to handle, but you don't want to breathe even the tiniest amounts of phosgene. Of course, you're correct in assuming that if there's any ammonia
left, it would react with the phosgene as it forms. Likely there is still some ammonia in it, but if not, you really don't want to get a nasty
nosebleed that doesn't show up for 24 hours.
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Dr.Bob
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We use solutions of ammonia in DCM and CHCl3 (most often with 10-20% MeOH) routinely at work, have not seen any issues with them. Simply washing the
DCM with 1.0 n HCl or NaHSO4 would remove most NH3, then dry and distill or use as is, if purity is not an issue. If you are concerned, you could
distill the bulk of it, just don't heat it to dryness if you have any fears, rotovap or low vacuum distillation would also work, but yields will be
low if you don't cool it very well.
[Edited on 7-8-2017 by Dr.Bob]
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woelen
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Nothing to worry about. It certainly will not ignite or explode.
If you want to dispose of it, just let it evaporate in contact with air. Add a little more 5% ammonia (e.g. 20% of its original volume), swirl so that
it mixes, and then put all of it in a plate so that the DCM evaporates. What remains behind is mainly water with some ammonia left in it. If there
were any peroxides (which I strongly doubt) then they will be harmless due to all the water present. If there were any phosgene (which I also strongly
doubt) then it will be destroyed by the ammonia.
If you want to keep the DCM, add a little dilute H2SO4 or a little dilute H3PO4 (both acids are non-volatile) so that any ammonia is bound to the
aqueous layer as ammonium ion. Next, add a tiny amount of ethanol (e.g. 0.5 ml for each 100 ml of DCM) just to be sure that no phosgene survives.
Swirl the mix and then distill out your DCM. What remains behind is an aqueous liquid containing acid and most of the ethanol. Your recovered DCM may
look somewhat cloudy, because you always will get a little water in it with the distillation. It will, however, be free of acid if H2SO4 or H3PO4 is
used for neutralizing ammonia and it will be free of ammonia, because all of that is bound to the aqueous layer as ammonium ion. The cloudiness can be
removed by drying with MgSO4 or CaCl2.
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alking
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Thanks guys, so it doesn't sound dangerous at all fortunately. I'll wash it with some H2SO4:H2O to neutralize any NH3 and remove any possible alcohols
(can't remember what I used this for after all and MeOH could be present), then vacuum distill it with a bit of H2SO4:H2O on the chance there are any
harmful side products present and so that I can recover it all, dry over whatever, and I'm done.
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