wakatutu
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Br2 in DCM
Hello everyone! Long-time reader of the forum, I'll get to my introduction later on somewhere else.
On two different occasions, I was experimenting with brominating vanillin in DCM utilizing a biphasic system with strong stirring in the temperature
range of 0-5C in an open beaker covered only by a watchglass. On both occasions I experienced strong respiratory discomfort despite successfully
keeping everything well below the boiling point of anything involved. A fume hood was not in use, but strong ventilation of the work area was
constant. On the second occasion a characteristic of strong bromine exposure was noted, which was a burning sensation in the mouth.
The procedure, as per lab notes:
30.4g Vanillin was dissolved in 250ml DCM. 30g H2SO4 was slowly added to
80ml H2O. This was added with cooling to 22.6g NaBr in 50ml H2O, and the
aqueous and organic solutions were added to the same beaker (not necessarily "combined") and vigorous magnetic stirring was begun. Using a salt-ice
bath, the temperature was kept at around 0-5C. Over the course of 2 hours, 19.3g of 35% H2O2 was added in small pipette loads. Slowly a precipitate formed and the DCM became visibly black-red with Bromine.
My concern is that with the oxidizers present (sulfuric acid, bromine, hydrogen peroxide), there could be a mechanism of oxidizing DCM to the dreaded
phosgene. I have searched extensively but have not been able to find any references to this being a known reaction, with the only indicator that DCM
can be oxidized to phosgene being reported from people using DCM in an enclosed, poorly ventilated space in close proximity to a strong heat source.
The only other possibility I can think of, beside the obvious use of personal protective equipment, is that I have an unusual sensitivity to bromine.
Another interested individual was in vicinity of the reaction and experienced no ill effects, lending some credit to the notion that I am simply very
sensitive to bromine and should avoid its use.
Also, I was under the impression that DCM solutions of bromine are less prone to off-gassing bromine vapours than the halogen itself, and in the past
I have worked with bromine in DCM to affect different bromination reactions, just not with the in-situ generation of the solution.
Any ideas?
Also, complete recovery from the respiratory discomfort the first time took only about 24 hours, but the recovery from the second time was
significantly longer, around 7 days. This supports my theory that I am developing an "allergy" to bromine, and I naturally have no intention of
trying this reaction again! Just wanted to know - bromine or possibly phosgene?
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Tsjerk
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Bromine is nasty stuff, I don't think you are sensitive, everyone is affected by it, you were just closer by than your colleague and got a bigger
whiff. Don't do this stuff without a fumehood!
About the reaction ; I would worry about oxidation of your aldehyde, not that of DCM. I used DCM in brominations to catch the bromine in a separate
reaction first ( in a seperatory funnel), then to add only the DCM layer. Works great in avoiding working with pure bromine and definitly keeps it
from evaporating quite well. I was still doing this in a fumehood though, halogens are nasty stuff to breath in.
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JJay
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Bromine is super nasty and shouldn't be handled indoors outside of a fume hood. Handling it requires protective gear including a lab coat and goggles
or face shield plus thiosulfate on hand for neutralizing spills, not to mention a ready respirator.
Working with DCM doesn't necessarily require a fume hood, but it shouldn't be handled in an unventilated area. I definitely don't suggest distilling
DCM in your kitchen or bedroom unless you like nosebleeds for some reason.
Edit: I should probably add that bromine is actually one of my favorite chemicals to work with, although it definitely does need to be treated with
respect.
[Edited on 23-2-2017 by JJay]
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MrHomeScientist
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Sensitization is definitely a possibility. I've become much more sensitive to smells since getting into home chemistry; for example mopping with
dilute ammonia never used to bother me but now it's instant headache. Recently working with tetralin was not a fun experience either. Anecdotal I
know, but sensitization to chemicals is well known and occurs with many different chemicals.
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Amos
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I'd advise getting yourself some ground glass equipment; adding the hydrogen peroxide via a pressure-equalizing addition funnel in one neck of a
two-neck flask with an efficient condenser on the other should cut down massively on fumes. Or at least drop your H2O2 down a condenser into your
reaction.
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Melgar
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I wonder if there couldn't be some side reaction replacing the chlorine in DCM with bromine. It's possible, especially if there's a catalytic amount
of aluminum present, and the bromine ever takes the form of HBr, which it often does in brominations. I've actually had that with iodine. I tried to
collect iodine precipitate with DCM, since it's heavier than water, but afterwards, it was a dark liquid that only evaporated very slowly. I thought
maybe it was an azeotrope, so I put it in a glass vial with a thin plastic lid, counting on DCM's famous ability to escape through plastic. Well,
whatever I had took an awfully long time to escape the plastic, and it left behind a purplish-brown residue in the plastic as it did. It never
solidified, although I doubt it was pure anyway, whatever it was. My guess is chloroiodomethane with iodine dissolved in it, but really, it could
have been anything.
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wakatutu
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Thanks for the responses!
I do not plan on working with this particular reaction mixture again. The recommendation of doing the reaction in a sealed flask with a
pressure-equalizing addition funnel would be absolutely the bare minimum of safety precautions I would take after my terrifying experience of thinking
"I did it this time!" and suffering pain in my lungs taking a week to resolve.
A respirator is on my shopping list now, and the construction of a fume hood seems a very modest inconvenience when compared to damaging my only set
of lungs. And this is just to minimize my overall exposure to chemicals. It's a fun hobby but I really like being alive and see no reason to
continue it without taking what I now realize are necessary precautions.
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BromicAcid
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There are preparative methods of oxidizing chloroform to phosgene using sulfuric acid and sulfur trioxide and/or dichromate. But I don't know about
the system you present here.
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Amos
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I'm still surprised this was such an issue for the OP. They handed bromine in DCM to college sophomores in my organic lab class two years back to work
with outside of a fume hood. Nobody seemed to encounter any discomfort.
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wakatutu
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I have concluded that I am allergic to bromine. Like I said, my associate was there as well and encountered no problems. Will not be working with
the particular halogen again. A small price to pay for living a healthy happy life. Thank you all for your contributions to my understanding of the
situation.
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Tsjerk
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You do realize that an allergy means your immune system recognizing a compound through a receptor right? I would be highly surprised if your immune
system would react to a halogen specifically.
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wg48
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Quote: Originally posted by Tsjerk  | | You do realize that an allergy means your immune system recognizing a compound through a receptor right? I would be highly surprised if your immune
system would react to a halogen specifically. |
I would be a little surprised too but its not unprecedented some simple compounds combine with some of your own body components to produce antigens.
Then there is zinc fume fever. If you inhale some of the fumes given off by molten zinc you can develop flue like symptoms, probably an immune system
response though it may be the size and reactivity of the particles as opposed to single molecules of the fume (zinc/zinc oxide).
I tried to remeber an example like posion ivy. I found the following on wiki:
Haptens are small molecules that elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also
does not elicit an immune response by itself. (In general, only large molecules, infectious agents, or insoluble foreign matter can elicit an immune
response in the body.)
[Edited on 25-2-2017 by wg48]
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pyro2525
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I would have to agree with the suggestion for using ground glass jointware. I have prepared bromine in DCM in a sep funnel, as Tsjerk mentioned, many
times and it is very possible to do this safely without a fume hood ("good" ventilation or a vent tube leading outside is required).
One issue is the addition of concentrated hydrogen peroxide can lead to production of oxygen gas (Br2 + H2O2), this oxygen production will essentially
cause bromine to vapourize. Ergo, add drip-wise rather than aliquot-wise.
That being said, DCM is just not really a good solvent for making 5-bromovanilin (I wish it was). Glacial acetic acid is Much better than either DCM
or MeOH. Product precipitation is faster and yield is higher in GAA.
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tsathoggua1
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It would not be impossible, methinks, for an intolerance greater than that of the 'background' level of the general population to develop to such a
simple molecule as Br2. Remember that people have become intolerant to H2O. Seems paradoxical, but it happens.
Sounds like it sucks ass too. I know all too well what its like to have something horrid generated in one's own saliva, albeit in my case it was
transient and mercaptan-ish. An intolerance to H2O would be even worse from the sound of it.
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wakatutu
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Thank you again for your concern. The health effects of my bromine exposure have now worn off and I can breathe easy again. I saw a doctor about
it, and after some fairly quick stethoscope action I was told to expect to expectorate and feel occasional pains but not to worry about long-term
damage. The pain dropped off after a couple weeks and the expectoration returned to a normal level for a smoker after a couple more weeks. Be
careful with this stuff!
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Sulaiman
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I'm glad that you have recovered, bromine (or iodine or chlorine) gets right up my nose,
and, I admit, a little in my lungs (especially almost invisible chlorine)
I suspect that you have become psychologically sensitised, a logical self-defence mechanism ..
i.e. your brain is telling you that last time it hurt, so don't do it again 
CAUTION : Hobby Chemist, not Professional or even Amateur
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Panache
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And on a brighter note there are no long term health effects understood for mild exposure to chlorine bromine or iodine, just temporary naseau and
shortness of breath feelings.
Don't worry every day hundreds of people roll up to the emergency wards with exactly the same thing.
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