Question

Explain the following:

A small amount of ethanol should be added to chloroform before its packaging.

Answer 1

1. Chloroform slowly oxidises on exposure to air, light or impurities to form phosgene (COCl₂), a highly poisonous gas.
2. A small amount of ethanol is added as a stabiliser because it reacts with any phosgene as it forms.
3. The trapping reaction converts phosgene into an organic chloroformate and HCl (e.g. \[\ce{COCl2 + C2H5OH -> C2H5OCOCl + HCl}\]).
4. Only a very small fraction of ethanol is used (typically a few tenths of a percent up to ≈0.5–1% v/v).
5. This amount is enough to prevent dangerous phosgene buildup without materially changing the solvent’s properties.
6. Ethanol also helps quench reactive intermediates, slowing further oxidative decomposition.
7. This measure reduces the storage hazard but does not make chloroform safe hazards remain.
8. Even stabilized chloroform must be stored cool, dark and tightly closed and handled in a fume hood with PPE.
9. Never store chloroform contaminated with acetone or alkali, and dispose of old or suspect stocks as hazardous waste.
10. Ethanol is added to trap phosgene and slow oxidation, thereby lowering but not eliminating the danger of stored chloroform.