Chemistry chlorofluorocarbons

F. S. Rowland and M. Molina showed that man-made chlorofluorocarbons, CFCs, could catalytically destroy ozone in the stratosphere (Nobel Prize for Chemistry, with P. Crutzen, 1995). 

Chemistry (Continued) polyimide, 287-300 polyurethane, 222-236, 546 transition metal coupling, 483-490 Chiral conjugated polymers, 479-480 Chlorinated solvents, 91 Chlorofluorocarbons (CFCs), 201, 205 Chloroformate endgroups, 87 Chloromethylation, 354 Church, A. Cameron, 431 Circular dichroism, 490 Classical catalysts, 433 Clean Air Act of 1990, 201, 205 Clearcoat, 240... 

A typical example of the interaction between hypothesis and experiment is the story of the work that resulted in worldwide concern over the depletion of the ozone layer in the stratosphere. These studies led to the awarding of the 1995 Nobel Prize for Chemistry to Paul Crutzen, Mario Molina, and F. Sherwood Rowland. Figure FT provides a schematic view of how this prize-winning research advanced. It began in 1971 when experiments revealed that chlorofluorocarbons, or CFCs, had appeared in the Earth s atmosphere. At the time, these CFCs were widely used as refrigerants and as aerosol propellants. Rowland wondered what eventually would happen to these gaseous compounds. He carried out a theoretical analysis, from which he concluded that CFCs are very durable and could persist in the atmosphere for many years. 

Until recently, chlorofluorocarbons (CFCs) for refrigeration were major end products of HF chemistry, but these compounds are being phased out in accord with the Montreal Protocols because of their effect on the ozone layer (see Chapter 15). 

Elliott AJ (1994) Chlorofluorocarbons. In Organofluorine Chemistry Principles and Commercial Applications (Eds RE Banks, BE Smart, and JC Tatlow), pp. 145-157. Plenum Press, New York. 

Terrence Collins is the Thomas Lord Professor of Chemistry at Carnegie Mellon University who contends that the dangers of chlorine chemistry are not adequately addressed by either academe or industry, and alternatives to chlorine and chlorine processors must be pursued. He notes, Many serious pollution episodes are attributable to chlorine products and processes. This information also belongs in chemistry courses to help avoid related mistakes. Examples include dioxin-contaminated 2,4,5-T, extensively used as a peacetime herbicide and as a component of the Vietnam War s agent orange chlorofluorocarbons (CFCs) polychlorinated biphenyls (PCBs the pesticides aldrin, chlordane, dieldrin, DDT, endrin, heptachlor, hexachlorobenzene, lindane, mirex, and toxaphene pentachlorophe-... 

Figure 12.45 summarizes the most important chemistry of bromine in the stratosphere, both gas phase and heterogeneous (shown as the darker lines). Once the bromine-containing organics reach the stratosphere, they absorb light and photolyze in a manner analogous to the chlorofluorocarbons. As seen in... 

Hayman, G. D., M. E. Jenkin, T. P. Murrells, and C. E. Johnson, Tropospheric Degradation Chemistry of HCFC-123 (CF,CHCI2) —A Proposed Replacement Chlorofluorocarbon, Atmos. Environ., 28, 421-437 (1994). 

Over the past several decades, there has been increasing recognition in a number of areas of the environmental impacts, both realized and potential, of human activities not only on local and regional scales but also globally. This is particularly true of changes to the composition and chemistry of the atmosphere caused by such anthropogenic activities. One example, for which there is irrefutable evidence, is stratospheric ozone depletion by chlorofluorocarbons, discussed in detail in Chapters 12 and 13. 

Ko, M. K. W., N. D. Sze, and G. Molnar, Global Warming from Chlorofluorocarbons and Their Alternatives Time Scales of Chemistry and Climate, Atmos. Environ., 27A, 581-587 (1993). 

In 1974, F. Sherwood Rowland and Mario Molina, who shared the 1995 Nobel Prize in Chemistry with Crutzen, showed that chlorine from photolyzed chlorofluorocarbons (CFCs) such as CF2C12 and CFCI3, which were used as supposedly inert refrigerants, solvents for cleaning electronic components, plastic foam blowing agents, and aerosol spray propellants, can also catalyze ozone loss. Subsequently, the chlorine monoxide molecule CIO, which is involved in the chlorine-catalyzed ozone destruction cycle, has been shown to be present in the holes in the ozone layer and to correlate inversely with... 

F. S. Rowland, Chlorofluorocarbons and the depletion of stratospheric ozone Am. Sci. 77, 36-45 (1989) T.-L. Tso, L. T. Molina, and F. C.-Y. Wang, Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride and ice release of active chlorine. Science 238, 1253-1260 (1987) J. G- Anderson, D. W. Toohey, and W. H. Brune, Free radicals within the Antarctic vortex the role of CFCs in Antarctic ozone loss. Science 251, 39-46 (1991) P. S. Zurer, Complexities of ozone loss continue to challenge scientists. Chem. Eng. News June 12, 20-23 (1995). 

R. S. Stolarski, The Antarctic Ozone Hole, Scientific American, January 1988. The 1995 Nobel Prize in Chemistry was shared by Paul Crutzen, Mario Molina, and F. Sherwood Rowland for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone. Their Nobel lectures can be found in P. J. Crutzen, My Life with 03, NO, and Other YZO Compounds, Angew. Chem. lnt. Ed. Engl. 1996,35, 1759 M. J. Molina, Polar Ozone Depletion, ibid., 1779 F. S. Rowland, Stratospheric Ozone Depletion by Chlorofluorocarbons, ibid., 1787. 

Sensors or analyzers exist for some of the priority analytes, such as 09, pH, and N03 . The challenge in these cases is to improve sensor stability, response rates, or lifetime. However, for most of the priority analytes, there is no existing sensor or analyzer system that will operate for long time periods without operator intervention. The development of sensors for most of these analytes, such as chlorofluorocarbons or dissolved iron, must circumvent the difficulties posed by low analyte concentrations or interference from other dissolved material. Development of specific sensing chemistry is the ultimate means of circumventing these problems. 

For many years chlorofluorocarbons (CFCs) were manufactured in huge quantities by Swarts-type processes but, after the introduction of the Montreal Protocol legislation, these compounds were superseded by non-ozone depleting HFCs (see Chapter 1). Fortunately, much of the chemistry developed for the manufacture of the CFCs can be adapted for the production of HFCs [7, 12-15]. 

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