Chemical reactivity chlorofluorocarbons

Another important mutagen is ultraviolet light. Recent concern about the depletion of the atmospheric ozone layer by chlorofluorocarbon compounds (CFCs) is due to the role of the ozone in absorbing UV radiation before it can cause mutations in the organisms at the earth s surface. All the DNA bases efficiently absorb UV and become chemically reactive as a result. The formation of pyrimidine dimers from adjacent thymidine residues in DNA interferes with replication and transcription of DNA. See Figure 8-14. 

Air pollution (qv) problems are characteri2ed by their scale and the types of pollutants involved. Pollutants are classified as being either primary, that is emitted direcdy, or secondary, ie, formed in the atmosphere through chemical or physical processes. Examples of primary pollutants are carbon monoxide [630-08-0] (qv), CO, lead [7439-92-1] (qv), Pb, chlorofluorocarbons, and many toxic compounds. Notable secondary pollutants include o2one [10028-15-6] (qv), O, which is formed in the troposphere by reactions of nitrogen oxides (NO ) and reactive organic gases (ROG), and sulfuric and nitric acids. 

Chemical plant safety, 68 Chemical stability/reactivity assessment, 68 Chemical vapour deposition (cvd), 69 Chlorinated paraffins, 69 N-chlorinated phosphorus amides, 69 Chlorinated poly(dimethylsiloxanes), 69 Chlorinated rubber, 69 Chlorine-containing systems, 70 Chlorite salts, 70 Chlorofluorocarbons, 71 N-Chloronitroamines, 71 Chlorophyll, 71... 

Some halogen compounds have been too reactive for the health of people and the planet. They can destroy healthy cells and attack the Earths atmosphere in the same active way that they kill germs or break down wood into paper. For instance, chlorofluorocarbon (or CFC) compounds used to be popular cooling chemicals in refrigerators and air conditioners and in the gas that pushed hairspray and deodorant out of aerosol cans. CFCs are now widely banned because they destroy Earths atmosphere. Chlorine is also part of the insect killer DDT, a dry cleaning fluid, and the compounds called PCBs. All of these products are now banned or used rarely because they have been linked to pollution and health problems like cancer and liver disease. 

Of all the elements, fluorine is the most reactive and the most electronegative (a measure of tendency to acquire electrons). In its chemically combined form, it always has an oxidation number of -1. Fluorine has numerous industrial uses, such as the manufacture of UF6, a gas used to enrich uranium in its fissionable isotope, uranium-235. Fluorine is used to manufacture uranium hexafluoride, SF6, a dielectric material contained in some electrical and electronic apparatus. A number of organic compounds contain fluorine, particularly the chlorofluorocarbons used as refrigerants and organofluorine polymers, such as DuPont s Teflon. 

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