ABSTRACT
The availability of chlorine by electrolysis made the production of chlorinated hydrocarbons possible on an industrial scale. These included chlorinated methanes, ethanes, and ethylenes. These compounds became widely used as solvents and chemical intermediates. Their advantages included relatively high chemical stability and low flammability. Extended use, however, revealed health hazards and resulted in restriction on exposure and use. The discovery of 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)ethane (DDT) in 1939 opened a new era in insect control and contributed to the elimination of malaria in many parts of the world. However, DDT and several related chlorinated insecticides were found to be persistent in the environment and to be detrimental to some species of birds, amphibians and fish. Most uses have been banned by international agreement. Chlorofluoro derivatives of methane and ethane, known as chlorofluorocarbons were found to have excellent properties as refrigerants and aerosol propellants. These, too, turned out to be persistent for decades in the atmosphere and stratosphere and to lead to polar ozone depletion. They were phased out under the Montreal Protocols adopted in 1987. They were replaced by hydrochlorofluorocarbons, which have much shorter half-lives, but contribute to atmospheric warming. They are scheduled to be replaced by 2020.
