Chlorofluorocarbons common

Chemicals that possess a common structural feature are called congeners. Some common examples are polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), poly-brominated diphenylethers (PBDE) and chlorofluorocarbons (CFC). The common features... 

Nontoxic chlorofluorocarbons, 24 188 Nontronite (iron smectite), 6 664, 696 structure and composition, 6 669 Nonuniqueness, 24 446 Nonvessel operating common carriers (NVOCC), 25 328 Nonvolatile compounds, as taste substances, 11 566 Nonvolatile food components,... 

Unlike petroleum hydrocarbons, organic compounds in general followed a different evolutionary path. Chlorinated solvents are a common group of organic compounds, and are also the most frequently encountered contaminant in groundwater. Common industrial chemicals that are characterized as chlorinated solvents include trichloro-ethene (TCE), 1,1,1-trichloroethane (TCA), tetrachloroethene (PCE) or perchloro-ethylene, chlorofluorocarbon (Freon)-113 (i.e., 1,1,2-trichloroethane or 1,2,2-tri-fluoroethane), and methylene chloride. In 1997, the EPA reported the presence of TCE and PCE in 852 of 945 groundwater supply systems throughout the United States and in 771 of 1420 Superfund sites. 

The chemical structure for common chlorinated solvents is shown in Figure 4.5. Chlorinated solvents such as TCE and PCE are composed of double-bonded carbon or ethylene structures with three and four chlorine atoms, respectively. The ethane derivative 1,1,1-TCA has three chlorine atoms. Freon is a chlorofluorocarbon and is also an ethane derivative with four chlorine atoms and three fluoride atoms. 

Amorphous fluoropolymers have many applications in the areas of advanced materials where they are used in applications requiring thermal and chemical resistance. Their manufacture is hindered by their low solubility in many solvents. Many fluoropolymerizations cannot be carried out in hydrocarbon solvents because the radical abstraction of hydrogen atoms leads to detrimental side reactions. Chlorofluorocarbons (CFCs) were thus commonly used, but their use is now strictly controlled due to their ozone depleting and greenhouse gas properties. Supercritical carbon dioxide is a very attractive alternative to CFCs and it has been shown that amorphous fluoropolymers can be synthesized by... 

The chlorofluorocarbon compounds of methane and ethane are collectively known as freons. They are extremely stable, unreactlve, non-toxic, non-corrosive and easily liquefiable gases. Freon 12 (CCI2F2) Is one of the most common freons In Industrial use. It Is manufactured from tetrachloromethane by Swarts reaction. These are usually produced for aerosol propellants, refrigeration and air conditioning purposes. By 1974, total freon production In the world was about 2 billion pounds annually. Most freon, even that used In refrigeration, eventually makes Its way Into the atmosphere where It diffuses unchanged Into the stratosphere. In stratosphere, freon Is able to Initiate radical chain reactions that can upset the natural ozone balance (Unit 14, Class XI). 

When some of the chlorines are replaced by hydrogens, CFCs become HCFCs, the now more common nomenclature for those chlorofluorocarbons containing hydrogen. The numbering is the same. When more than one isomer is possible, the most symmetrically substituted compound has only a number letters a and b are added to designate less symmetrical isomers. 

In the early 1970s, Mario Molina (b. 1943) of the Massachusetts Institute of Technology, F. Sherwood Rowland (b. 1927) of the University of California, Irvine, and Paul J. Crutzen (b. 1933) of the Max Planck Institute in Germany, all shown in Figure 17.16, recognized the potential threat to stratospheric ozone posed by chlorofluorocarbons (CFCs). Because CFCs are inert gases, they were once commonly used in air conditioners and aerosol propellants. Two of the most frequently used CFCs are shown in Figure 17.17. 

CARBON TETRACHLORIDE. [CAS 56-23-5], CCL, formula weight 82.82. heavy, colorless, nonflammable, noncombustible liquid, nip - 23°C. bp 76.75 C. sp gr 1.588 <2S C/25lC). vapor density 5.32 (air = 1.00). critical temperature 283.2cC. critical pressure 661 atmospheres, solubility 0.08 g in 100 g H 0. odor threshold 80 ppm. Dry carbon tetrachloride is noncorrosive to common metals except aluminum. When wet. CCL hydrolyzes and is corrosive to iron, copper, nickel, and alloys containing those elements About 9091 of all CCL manufactured goes into the production of chlorofluorocarbons ... 

Techniques used to study fast reactions all monitor concentration spectroscopically, as described in Major Technique 2. For instance, suppose we were studying the effect of a chlorofluorocarbon on the concentration of ozone, a blue gas. We could use a spectrometer to monitor the absorption responsible for the color and interpret the intensity of absorption in terms of the molar concentration of 03 molecules. In the stopped-flow technique, solutions of the reactants are forced into a mixing chamber very rapidly and the formation of products is observed spectroscopically (Fig. 13.3). This procedure is commonly used to study biologically important reactions. 

Roy Plunkett did not set out to invent Teflon. He discovered this polymer by accident while working in a lab in 1938. Plunkett was trying to make a new chlorofluorocarbon (CFC)—a chemical compound that contains chlorine, fluorine, and carbon and used to be a common ingredient in aerosol spray propellants, degreasing agents, foam packing material, and refrigerants. 

Hydrochlorofluorocarbons (HCFCs) are now being produced in very large quantities as substitutes for ozone-depleting chlorofluorocarbons (CFCs). The two most common HCFCs are 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-l-fluoroethane (HCFC-141b) ... 

Common uses for the fluorocarbons are as refrigerants, foam-blowing agents, solvents, and fluoropolymers. Recent environmental legislation has restricted or banned the use of chlorofluorocarbons. 

Halocarbons, a class of polar solvents, are hydrocarbons with an attached halogen. There are commonly three types of halocarbon solvents those based on chlorine, fluorine, and a combination of the two. They are all powerful degreasing materials and can be particularly effective in removing polar contaminants from glass. The chlorofluorocarbons are currently under review because they cause environmental damage to the ozone layer.1... 

Clenil-Modulite contains HFA-134a, ethanol and glycerol. The propellant 1,1,1,2-tetrafluoroethane (HFA-134a) is a non-chlorofluorocarbon (CFC). Ethanol is commonly used in pharmaceutical formulations as a solvent and can act as a preservative and skin penetrant. Glycerol acts as a humectant, preservative and increases formulation viscosity. 

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