Trichloromethane (Chloroform)

Uses

Trichloromethane, $\text{CHCl}_3$, is universally known as chloroform. Chemically it serves as a solvent for fats, alkaloids, iodine, and a range of other substances. Today its biggest industrial use is as a feedstock in making the refrigerant freon R-22.

Chloroform has an older claim to fame: it was once widely used as a general anaesthetic during surgery. It has since been replaced by safer, less toxic anaesthetics such as ether, precisely because of the toxic effects described below.

Toxicity

Being an anaesthetic, chloroform vapour depresses the central nervous system when inhaled — that is exactly what made it useful as an anaesthetic in the first place, but it also makes it dangerous with unsupervised or prolonged exposure.

• Breathing air containing roughly 900 parts per million of chloroform for even a short time can bring on dizziness, fatigue, and headache.
• Chronic exposure can damage the liver (where chloroform is metabolised to phosgene) and the kidneys.
• Some people develop skin sores when the skin is immersed in chloroform.

Slow oxidation to phosgene, and how it is stored

Left in air and light, chloroform is slowly oxidised into an extremely poisonous gas, carbonyl chloride, better known as phosgene:

$2\text{CHCl}_3 + \text{O}_2 \xrightarrow{\text{light}} 2\text{COCl}_2 + 2\text{HCl}$ …