Chlorinated Hydrocarbons

A very large and diverse group of organic molecules are chlorinated hydrocarbons. Hydrocarbons are molecules composed entirely of hydrogen and carbon atoms, often derived from carbon-based fossil fuels like petroleum oils and coal. Chlorinated hydrocarbons are specific hydrocarbon molecules that also have atoms of the element chlorine chemically bonded to them. The number of chlorine atoms bonded to a specific chlorinated hydrocarbon determines, in part, the properties of the molecule. The number of carbon atoms and how they are arranged in three-dimensions also determines the chemical and physical properties of chlorinated hydrocarbons. Because there is such an immense number of possible forms of chlorinated hydrocarbons, this class of useful compounds has a wide set of applications that are of great economic and practical importance. For example, chlorinated hydrocarbons produced from the refinement of crude oil comprise such things as synthetic rubbers used in automobile tires and tennis shoes. They also create plastics used in packaging, and products like fluid pipes, furniture, home siding, credit cards, fences, and toys, to name just a few. Chlorinated hydrocarbons can also be used as anesthetics, industrial solvents, and as precursors in the production of non-stick coatings like Teflon. Chlorinated hydrocarbons are some of the most potent and environmentally persistent insecticides, and when combined with the element fluorine, they function as refrigerants called chlorofluorocarbons, or CFCs. Because of their wide array of uses, chlorinated hydrocarbons are among the most important industrial organic compounds. Since they are derived from distillates of petroleum fossil fuels, however, the depletion of global oil and coal reserves looms as a concern for the future.

Chloroform

Chloroform is a colorless liquid at room temperature and is very volatile. Characterized as having a heavy sweet odor somewhat like ether, chloroform is actually sweeter than cane sugar. Chloroform cannot mix well with water. Like salad oil in water, chloroform separates into a layer. However, it does mix well with other hydrocarbons, so one of its uses is as a solvent or cleaner to dissolve other organic substances like gums, waxes, resins, and fats. Also, chloroform is used in the industrial synthesis of the non-stick coating called Teflon (polytetrafluoroethylene), which is an organic polymer. However, in the past, the primary use for chloroform was as a general anesthetic.

General anesthetics are drugs that cause the loss of consciousness in order to avoid sensations of extreme pain, such as those encountered during surgery. First synthesized in the laboratory in 1831, chloroform was used as a general anesthetic for the first time in 1847 by British physician Sir James Simpson during an experimental surgical procedure. Before the discovery of chloroform's utility as a general anesthetic, drugs such as opium, alcohol, and marijuana were used to dull the pain of medical procedures. However, none were effective enough to allow pain-free surgery within the body. Other substances, like ether and nitrous oxide, were also used as general anesthetics around that same time. Because it was used for Queen Victoria of England's labor pain during childbirth in 1853, chloroform became very popular. It was soon discovered that chloroform can cause fatal cardiac paralysis in about one out of every 3,000 cases, and therefore is seldom used as an anesthetic today.

Carbon tetrachloride

Carbon tetrachloride, like chloroform, is a clear, organic, heavy liquid. Consisting of one carbon atom and four chlorine atoms, carbon tetrachloride has a sweet odor and evaporates very easily and so is most often encountered as a gas. The compound does not occur naturally. Rather, it is manufactured industrially in large amounts for use as a solvent to dissolve other organic materials, or as a raw material in the production of chlorofluorocarbons (CFCs) used as aerosol propellants and refrigeration fluids. For many years, carbon tetrachloride was used as a cleaning agent to remove greasy stains from carpeting, draperies, furniture upholstery, and clothing. Also, prior to 1960, carbon tetrachloride was used in fire extinguishers since it is inflammable. Because it is an effective and inexpensive pesticide, before 1986 carbon tetrachloride was used to fumigate grain. These applications, however, have been discontinued since the discovery that the compound is probably carcinogenic, or cancer causing. Given its potential to cause cancer in humans, carbon tetrachloride is especially dangerous since it does not break down in the environment very easily. It can take up to 200 years for carbon tetrachloride to degrade fully in contaminated soil. Fortunately, the carcinogenic effects seen in laboratory experiments were due to very high levels of exposure that are not characteristic of the levels encountered by most people. Currently, it is not known what long-term low levels of exposure might have on human health.

The chlorinated hydrocarbons discussed above are considered to be simple because they contain only one carbon atom in their molecules. Many chlorinated hydrocarbon substances, however, are much larger than this. Having molecules consisting of numerous carbon atoms, some of the most important examples of complex chlorinated hydrocarbons are polymers and biologically active compounds that act as poisons.