Chloroform, also known as trichloromethane, is a colorless, sweetly scented liquid with the chemical formula CHCl3. It is best known for its historical use as a general anesthetic, although this has since been abandoned due to safety concerns. Today, trichloromethane is used in a variety of industrial processes, including the manufacture of plastics, refrigerants, and solvents. It is found in small quantities in water and the atmosphere; most of this comes from natural sources. Chloroform is toxic and rapidly releases vapor when exposed to the air, so it should be handled with care.
This compound was originally made by the reaction of ethanol or acetone with bleaching powder — calcium hypochlorite. In modern times, however, it is manufactured industrially by combining methane with chlorine. Small amounts of the chemical are produced naturally by marine life, such as seaweeds, and by the decomposition of plant remains in the soil. The main human sources in the environment are from the use of chlorine as a bleaching agent in paper mills, and the chlorination of drinking water. The chlorine reacts with various organic compounds to produce trichloromethane, but the amounts present in chlorinated water are tiny and are not thought to pose any risk to human health under normal circumstances.
The use of chloroform as an anesthetic dates from 1847, but concerns were soon raised about its safety. In 1848, a patient died because her heart beat because rapid and irregular while she was anesthetized, and continued use only cemented the link between the chemical and cardiac events. By the early 20th century, the use of chloroform was in decline, and it was abandoned in favor of safer and cheaper alternatives by around 1940. Today, safer anesthetics such as halothane, isoflurane, and sevoflurane, and others are used. When a less expensive alternative is required, as is the case in some impoverished nations, ether, an older anesthetic, is often preferred.
Today, the biggest use of chloroform is in the production of polytetrafluoroethylene (PTFE), a relatively heat-resistant plastic best known for its use as a non-stick coating for pots and pans. The compound is first reacted with hydrogen fluoride to form chlorodifluoromethane, a compound used as a refrigerant and a propellant for aerosol cans. This use has been phased out in many countries, due to its effects on the ozone layer, but its production is still an important step in the manufacture of PTFE.
In the laboratory, trichloromethane is often used as a solvent, as it is stable, relatively unreactive, and dissolves many organic compounds. It is very effective in extracting substances from plant material and is used in this way in the pharmaceutical industry for extracting drugs and drug precursors from plants. It may also be employed in analytical chemistry to isolate compounds from samples and is used in the synthesis of many organic chemicals.
The anesthetic effects of chloroform are well known and are due to inhibition of central nervous system activity. Inhalation of the vapor can quickly bring about unconsciousness, but a very high dose can be fatal. The chemical also affects the activity in other major organs, including the heart, which makes it dangerous as an anesthetic. It is considered moderately toxic — in terms of acute effects — if swallowed, but a dose of 0.35 fluid ounces (10 milliliters) can be fatal in humans.
Long-term exposure to relatively low concentrations of trichloromethane can have a number of adverse effects, especially on the liver and kidneys. There may be a cancer risk associated with exposure to this chemical. Although there is no conclusive evidence of a cancer link in humans, tests on animals have shown chloroform to cause liver and kidney tumors, and in the US, the Environmental Protection Agency (EPA) has classified it as a “probable human carcinogen.” Exposure is most likely to occur in an industrial or laboratory setting, but small amounts of it are present in the atmosphere and in water. Since it does not react with many naturally occurring substances, it can take a long time to break down and may build up in groundwater.
Another potential risk in the handling and storage of chloroform is the formation of the highly toxic gas, phosgene, which was used as a chemical weapon during World War I. In the presence of light, trichloromethane reacts with oxygen in the air to produce this gas. For this reason, it is stored in dark glass bottles.