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Chloroform.
Phosgene could be lurking in the bottle
Legal requirements
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I am grateful to Frank Sugar for highlighting the Danger
of Phosgene generation from Unstabilized Chloroform link and to Mike
Threadgill for additional information.
Not a lot of people know
this;
IF
you are using chloroform which is older than about 6 months OR
which is NOT stabilised with ethanol OR has been dried (with e.g.
P2O5)
then you should be aware that Phosgene (used as a gas in World
War I) can accumulate in the bottle as a breakdown product of chloroform.
Mike Threadgill (former University Chemical Safety Adviser)
writes;
The danger of phosgene forming in chloroform is known to old-fashioned
chemists but is probably news to most people.
As I understand it, there is no problem with chloroform that has been
stabilised in the old-fashioned way, by addition of 1% of ethanol. All
chloroform supplied up to a few years ago was stabilised in this way (unless
you specified otherwise to the supplier). This stabilisation worked in
two ways. Firstly, the ethanol inhibited the formation of phosgene. Secondly,
the ethanol reacts with the phosgene to form diethyl carbonate (which
is relatively harmless).
More recently, chloroform has been supplied either without any stabiliser
or with 2-methylbut-2-ene, which is much less effective than ethanol but
is much less of a nuisance in chemical experiments.
So, if your chloroform has been stored for 2 years
and contains no ethanol, it may well contain some phosgene. If you are
using it in the fume cupboard (as you should be!), then there is probably
not much additional risk from the phosgene, when compared with the risk
from the chloroform vapour. However, your experiment may not like it!
Chloroform should ALWAYS be stored in the dark
and in securely closed bottles.
If you remove the ethanol stabiliser (e.g. by "drying" the chloroform
with P2O5),
then phosgene will be formed fairly rapidly (over a period of a few weeks).
March 2005.
I am also indebted to Dr Michael Wilson, Duncan Technology Center,
Oklahoma for this;
A co-worker and I were recently exposed to phosgene that had formed in
a wash bottle of chloroform. After several minutes of painful coughing
we did a little spectral analysis and realized that it was indeed phosgene
and not some other acid chloride.
During our internet search we ran across the safety article posted by
you where Mike Threadgill warns of possible phosgene contamination. I
am one of the old-fashioned chemists that Mike Threadgill refers to, so
I remembered some cautions about phosgene formation in chloroform. I copied
that article for our Safety Manager, so she could close a "near miss"
hazard investigation.
This chloroform was from a bottle of ethanol stabilized
chloroform, and it was not very old, BUT the plastic wash bottle was
a transparent fluorocarbon type and this particular sample may have been
sitting in the light (in the fume cupboard) for a period of months. Ultraviolet
light will accelerate the formation of phosgene.
A tip for NMR users of chloroform -d (which has no stabilizers): a few
bits of mossy zinc metal in the bottle will help reduce the formation
of unwanted phosgene and HCL.
J. Michael Wilson, Ph.D. Environmental Technical Excellence
Leader. Halliburton. Duncan Technology Center.
2600 S. Second St. Duncan, OK 73536-0438. USA
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