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Artemus Gordon
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DCM storage
I bought a pint of dichloromethane (methylene chloride) about 9 months ago from Elemental Scientific. It arrived in a soft plastic (PVC, I think)
bottle with a plastic screwtop with vinyl adhesive tape wrapped around the cap/bottle seam. I did not unseal it and I placed it where I store all of
my lab equipment, in an unused bedroom at the northeast corner of my house. Yesterday, while looking for another chemical, I fount my DCM bottle
collapsed and completely empty. So it appears that at some point during the summer the DCM had boiled and forced it's way past the lid.
That room is the coolest one in my house. it doesn't get direct sunlight except in the very last part of the afternoon, and I keep the curtains drawn.
However, I don't have A/C, so the whole house can get to 100 degF in the summer.
Obviously, a PVC bottle is no good for storing DCM under these conditions, but would a glass bottle be safe, or would I risk it exploding? I could
store my DCM in the refrigerator, but I don't like the idea of keeping lab chemicals with my food.
I did try to UTFSE, both here and Google in general, but nothing specific came up about DCM and warm rooms.
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gdflp
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The boiling point of DCM is 103°F, so I would expect the vapor pressure got too high and the bottle exploded. I would use caution storing it in
glass, you might have shards of glass all over right now instead of an empty bottle. DCM is a carcinogen with a high vapor pressure, so I wouldn't
store it in a refridgerator with food as you will risk contamination. The best way to store it would be to buy a lab freezer and store it in there,
or just distill some from paint stripper as needed.
[Edited on 12-1-2014 by gdflp]
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DraconicAcid
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When we bought dichloromethane for the lab, it regularly came in brown glass bottles. On a really warm day, they'd hiss when opened, but you'd have
to get it really hot for a bottle to explode.
I would be very hesitant to store any organic solvent in any plastic bottle long-term.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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forgottenpassword
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DCM has NOT been proven to be a carcinogen. It is suspected to be a carcinogen by
analogy with chloroform; which nevertheless was extremely-widely used to completely anaesthetise people by direct inhalation without causing everyone
(or in fact practically no-one) who received anaesthesia to develop cancer.
[Edited on 1-12-2014 by forgottenpassword]
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gdflp
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It is classified as Cat. 2, or R40 which means "Limited evidence of a carcinogenic effect". Other compounds in this class include cobalt salts and
lead salts. Therefore I would classify this as a carcinogen, even though DCM isn't necessarily a strong carcinogen. And a carcinogen is not
classified as instant cancer on exposure. Even confirmed potent carcinogens MAY cause cancer on exposure. So just saying that "everyone who received
anesthetic didn't develop cancer so it's not a carcinogen" is meaningless.
[Edited on 12-1-2014 by gdflp]
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forgottenpassword
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Fair enough. I'm talking about the real risk of handling and using it. I can't deny that it MAY cause cancer. Water MAY cause cancer too; so let's
call that a carcinogen, shall we? There is a non-zero probability that everything is a carcinogen. What IS meaningless is to ignore the fact that
millions of people were completely anaesthetised by long-duration inhalation of chloroform over decades without later-developing cancer. The
cancer-risk is not the reason that chloroform was removed from the anaesthesiologists table -- rather the invention of superior agents caused it to be
replaced. Besides, we are talking of DCM, not chloroform. If the cancer-risk of chloroform is so-low, that of DCM must be practically negligible.
As regards storage: I have some chloroform stored in a stainless steel bottle. I'm sure that DCM may be stored similarly. Wrap the screw top with some
PTFE plumbers tape to seal the screw-threads, and prevent the vapour from escaping.
[Edited on 1-12-2014 by forgottenpassword]
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gdflp
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Different carcinogens are more or less potent, it's all about what the likelihood is that a certain mutation will occur causing cancer. Water may
cause cancer, but the chance is minute. When a compound is classified as R40, or IARC Cat. 2, it's because studies or data have shown that the chance
of a mutation occuring is higher than a certain threshold. The threshold that generally classifies a carcinogen is "Will exposure to this compound
cause a statistically significant higher risk of cancer than an identical organism not exposed to it?" If this correlation is small, or there
isn't enough data a compound is classified as "suspected of causing cancer", but this doesn't mean than the compound has not been
proven in some studies to be a carcinogen, or that it doesn't carry a higher risk of causing cancer.
And how can you relate chloroform and dichloromethane? They are in the same class and have completely different effects. Benzene is a carcinogen
because of the metabolic pathway, but replace one of the hydrogens with a bromine atom and it ceases to be a carcinogen. You can't compare the
carcinogenic properties of even the most similar molecules can have different effects. Even enantiomers can have opposing carcinogenic properties.
[Edited on 12-1-2014 by gdflp]
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DraconicAcid
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Carcinogenic or not, I loathe the smell of DCM, and would be revolted at the idea of of storing it in a fridge with food.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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forgottenpassword
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Quote: Originally posted by gdflp  | And how can you relate chloroform and dichloromethane? They are in the same class and have completely different effects. Benzene is a carcinogen
because of the metabolic pathway, but replace one of the hydrogens with a bromine atom and it ceases to be a carcinogen. You can't compare the
carcinogenic properties of even the most similar molecules can have different effects. Even enantiomers can have opposing carcinogenic properties.
[Edited on 12-1-2014 by gdflp] |
Ok, good point! Have you seen evidence to suggest to you that it is a carcinogen? I was always under the impression that it was considered a "safer
form of chloroform". In fact, that is how it was presented to me. Perhaps that is wrong, and I would be better handling chloroform? As explained
above, I am (personally) satisfied that chloroform poses only a minimal risk to health.
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gdflp
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I have seen studies that suggest that both are mild carcinogens. DCM is generally considered safer due to lower acute, rather than chronic, toxicity.
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woelen
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DCM can be stored safely very well in a glass bottle with a tightly sealed cap. I have DCM stored in a brown glass bottle with a sturdy plastic cap
for many years and no noticeable amount of DCM escaped from the bottle. In summer the room can well go above 35 C (it is under a roof without airco)
and in winter the temperature can go as low as 5 C (only weak heating, preventing freezing). No problems for storing DCM.
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Chemosynthesis
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I have seen DCM in both glass reagent bottles and smaller commercial metal containers. The metal cannisters are often for solvent use (bathroom
refinishing, fiberglass resins, etc.). I can't recall if I have encountered DCM specifically in this next manner, but I have seen many solvents in
large capacity metal drums when running columns or the doing industrial scale syntheses. They do not leak (normally).
Let's not be silly comparing DCM to water; DCM is a confirmed animal carcinogen, mostly due to correlative inhalational studies on mice and rats, and
it is genotoxic to cells which include human cell lines, making it a probable human carcinogen. It is not merely presumed from extrapolating
toxicology data from other chlorinated hydrocarbons such as chloroform.
[Edited on 1-12-2014 by Chemosynthesis]
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Artemus Gordon
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| Quote: Originally posted by woelen | | DCM can be stored safely very well in a glass bottle with a tightly sealed cap. I have DCM stored in a brown glass bottle with a sturdy plastic cap
for many years and no noticeable amount of DCM escaped from the bottle. In summer the room can well go above 35 C (it is under a roof without airco)
and in winter the temperature can go as low as 5 C (only weak heating, preventing freezing). No problems for storing DCM. |
Thanks, woelen!
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careysub
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| Quote: Originally posted by gdflp | | I have seen studies that suggest that both are mild carcinogens. DCM is generally considered safer due to lower acute, rather than chronic, toxicity.
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DCM is considered safer for chronic toxicity as well.
A good rule of thumb about making comparisons like this (since they already crunched all the data) is to compare the OSHA TWA PEL limits (averaged
permissible vapor concentration for an 8 hr working day).
For benzene it is 1 ppm
For chloroform it is 2 ppm
For DCM it is 25 ppm
It is worth noting that although benzene has been shown to be associated with cancer risk in occupational settings, neither chloroform nor DCM has
ever shown any detectable cancer hazard in human populations. This means of course that the hazard is small enough to fall below the limits of
detectability, not that it does not exist, but is a useful reference point nonetheless.
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macckone
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Benzene is a known carcinogen which is a different class from suspected carcinogens. Even so, low exposure may not be a risk. The assumption is that
there is no safe exposure to carcinogens when in fact the body may be capable of dealing with some level. Since human experimentation is banned, we
will likely never know.
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careysub
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The issue of setting safety levels for carcinogens is more a policy question than a scientific one. Some policy decisions that have been made in this
area proved difficult to implement, or defend.
The nominal standard that safety agencies have wanted to implement is to keep the hazard to a one-in-a-million level, which is really, really safe -
but also arbitrary.
When applied to radiation this standard immediately runs into a serious problem. The hazard level due to natural, unavoidable radiation is at least
100 times higher than this, the one-in-ten thousand level. Natural variation (even excluding isolated natural very hot spots) is several times larger
than this baseline.
Furthermore the natural incidence of the disease caused by carcinogens - namely cancer - occurs in 1/3 of the population anyway. Unless it is a
particular type of rare cancer, tied to a specific carcinogen (e.g. mesothelioma and asbestos) it is impossible to detect small incremental increases
in cancer risk.
NIOSH adopted a standard back in the early 1970s that there was no acceptable exposure level to any known or suspected human carcinogen and that all
such exposures should be kept to "the lowest feasible level" - with the cost of that feasibility left unspecified.
This policy could not survive indefinitely as more and more data on weak carcinogens accumulated, detection techniques got better and better, and more
efficient and expensive control technologies developed. It was inevitable that NIOSH (as the EPA always did) would have to set an actual hazard level
and balance costs against it, rather than simply declaring "no carcinogens ever". They finally sent out a draft of a revised policy last year.
The new standard is "NIOSH will set RELs to keep exposures below the 95% lower confidence limit estimate of the dose expected to produce 1 in 1,000
excess risk of cancer as a result of a 45-year working lifetime exposure. Although NIOSH recommends keeping occupational carcinogen exposures below
the concentrations that produce a working lifetime risk of 1 in 1,000, this should be considered the minimum level of protection. Controlling
exposures to lessen risk is always warranted. A risk near 1 in 1,000 is at least an order of magnitude higher than the cancer risk permitted in the
United States for the general public."
In doing so they abandoned the hopelessly unrealistic one-in-a-million standard. It appears that the reality of natural radiation exposure has
informed this standard: the 1 in 10,000 risk permitted the general public is the same as the background radiation risk in a low radiation area. The 1
in a 1,000 occupational risk is just a bit higher than the radiation risk from living in certain areas of New England or Colorado.
| Quote: | | Benzene is a known carcinogen which is a different class from suspected carcinogens. |
True - it means we actually know the risk magnitude rather well, instead of just having an upper bound.
One reason that we know benzene is a human carcinogen is that it promotes one particular type of rare cancer: acute myeloid leukaemia.
| Quote: | | Even so, low exposure may not be a risk. The assumption is that there is no safe exposure to carcinogens when in fact the body may be capable of
dealing with some level. |
This does appear to be the case with benzene (exposures below 50 ppm in air may not be a hazard), but this can't be said to be a general rule.
For radiation current risk assessment practices assume a linear no-threshold model. There isn't good data to dispute this assumption - knowledge of
mechanisms and processes tends to support it.
| Quote: | | Since human experimentation is banned, we will likely never know. |
Human experimentation wouldn't help. Many worker populations, with tens or even hundreds of thousands of individuals ("natural experiments"), are too
small to detect cancer hazards from many carcinogens proven in animal models.
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NexusDNA
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Hey! Summoning this from the dead while there are still some earthworms.
I've just bought 1 liter of DCM which came in a amber glass bottle with a cap from sigma (the bottle is 90-95% full). While it's still closed I'm
keeping it in the freezer, because outside it gets easily to 40ºC. Inside a cupboard I think it can get up to 35ºC. Can it be stored safely or will
the cap pop out?/any suggestions?
Bromine, definitely bromine.
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Chemosynthesis
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http://www.solvaychemicals.com/Chemicals%20Literature%20Docu...
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Zombie
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Why not buy a Mini fridge for volatile chemicals?
That is on my to do list...
They are as low as 80 bucks...
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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gdflp
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I would opt for a small freezer rather than a fridge. Typically, I find that chilling something to -20°C is much more useful than chilling something
to 0°C, which can be accomplished with an ice bath.
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MrHomeScientist
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That's what I did, Zombie. Very very handy thing to have in the lab, and pretty inexpensive. A lab freezer would be great too, or the
fridge-with-a-freezer that is pictured above would be ideal. Mine doesn't have a freezer compartment unfortunately. The next handy appliance I'm
looking forward to including in the lab is a toaster oven. I got a new one for my birthday, and the old one still works great so it's on its way to
the lab for drying and dehydration duty!
Edit: to be more on topic, I also have DCM (distilled from paint stripper) that I keep in this fridge. I think it is very slowly leaking out (mild
smell), so a freezer would be a better choice.
[Edited on 3-5-2015 by MrHomeScientist]
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Sulaiman
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According to Wikipedia,
DCM has a vapour pressure of 1 atmosphere at 40.7C
so it should not be difficult to contain.
http://en.wikipedia.org/wiki/Dichloromethane_%28data_page%29
[Edited on 5-3-2015 by Sulaiman]
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NexusDNA
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Ok! Yeah, when i build a proper lab I'll buy a freezer, but right now I don't have the money (though i do have a toaster oven  ). I'll try to leave it out of the freezer during the afternoon to see if it the cap
can handle the pressure.
Those Schott bottles with blue cap (like this one) have a tight seal or are leaky?
Bromine, definitely bromine.
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Chemosynthesis
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Woops. Left out the other value you'd need for Clausius Clapeyron. Way to go copy and pasting skills.
Those bottles seal pretty tightly from my experience.
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Molecular Manipulations
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If you're worried about about something exploding from pressure buildup, use a ground glass reagent bottle with a GG stopper. That's what I use for
very volatile substances. If the pressure gets too high it'll just lift the stopper enough to let some pressure out. Now there's no need for this with
DCM, but for more volatiles this works great. I've stored liquid dinitrogen tetroxide like this (in my lab fridge).
-The manipulator
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