August 2020: A laboratory worker opened a bottle containing ~3L un-stabilized chloroform on the bench top. Upon opening, a noticeable vapor cloud was released from the bottle. Suspecting that the vapor cloud may be phosgene, the laboratory worker immediately closed the bottle and placed it in the chemical fume hood. Upon carefully reading the bottle label, which was very faded (see adjacent photo), it was determined that the chloroform expired in 1990.
Phosgene is a toxic gas that can be formed when chloroform is exposed to oxygen in the presence of UV light (or other catalytic contaminants), especially in the absence of stabilizers (e.g. ethanol). It is often characterized as having a “fresh cut hay or grass” odor. While the laboratory worker did not detect this odor, and the exact composition of the vapor cloud was not determined, the presence of phosgene was presumed given the age of the chemical.
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