Chlorofluorocarbons compounds

C04-0158. CF3 CH2 F (HFC-134a) has replaced chlorofluorocarbon compounds for use as refrigerants. HFC-134a is produced from trichloroethylene by the following reactions ... 

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). 

Chlorine can be substituted by hydrogen fluoride and boron trifluoride to yield chlorofluorocarbon compounds. This process is applied for producing 1,1-dichloro-l-fluoroethane (14), which is considered as a replacement for trichlorofluoromethane as a blowing agent for plastic foam.18... 

There have been extensive investigations into the kinetics of disproportionation reactions involving chlorofluorocarbon compounds.4-6 Phase equilibrium constants in relation to contact time and temperature have been determined and reported in various publications.1-3... 

Chou, C.C., Milstein, R.J., Smith W.S., Vera Rutz, H., Molina M.J. and Rowland, F.S. (1978) Stratospheric photodissociation of serveral staruated perhalo chlorofluorocarbon compounds in current technological use (Fluorocarbons -13, -113, -114, and -115), J.Pkys.Chem. 82,1-7. 

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. 

Loss of CFC-113 from tissues is rapid during the postexposure period with virtually 100% clearance within 24 h of exposure. Freons are eliminated entirely by the respiratory tract. Chlorofluorocarbon compounds partition preferentially into lipid-rich tissues and are poorly metabolized. Significant accumulation occurs in brain, liver, and lung tissues compared to blood levels. 

Chlorofluorocarbon compounds are cardiac sensitizing agents. Pulmonary edema, bronchial constriction, and lung irritation may also occur following inhalation exposure to high chlorofluorocarbon concentrations. 

Ozone (O3) exists in the atmosphere, 20-40 km above sea level. Ozone absorbs UV radiation which would otherwise harm living things. The effects of ozone loss could include increased human cataracts and skin cancer, reduction of plankton in ocean waters and destruction of plants, including crops. Ozone layer destruction in the Antarctic was reported in 1985 a major cause of this was believed to be the release of chlorofluorocarbon compounds, such as CCI2F2 (CFCs). These compounds are chemically unreactive, non-toxic and odourless, properties which at one time caused them to be used as solvents, aerosol propellants, refrigerant fluids and blowing agents for expanded plastic foams. They are so stable, however, that they persist in the atmosphere for years and eventually enter its upper layers, where they are broken down by the powerful UV radiation emitted by the sun. Their decomposition products can then destroy ozone ... 

Ozone depletion potential represents the potential of depletion of the ozone layer due to the emissions of chlorofluorocarbon compounds and other halogenated hydrocarbons. 

Fluorine compounds have many uses. One of the most notable of these is the manufacture of chlorofluorocarbon compounds known by the trade name Freon. These are chemical combinations of chlorine, fluorine, and carbon, an sample of which is dichlorodifluoromethane, CI2CF2. These compounds used to be widely employed as refrigerant fluids and blowing agents to make foam plastics they were also once widely used as propellants in aerosol spray cans. Uses of chlorofluorocarbons have now been phased out because of their role in destroying stratospheric ozone (discussed with oxygen, above). 

Chlorofluorocarbons Compounds formed when some or all of the hydrogen atoms in a hydrocarbon (typically an alkane) have been replaced with chlorine and fluorine.They are inert substances that have been used widely as refrigerants and as propellants in aerosol cans. Their use is being discontinued as they have been implicated in the destruction of the ozone layer above the Earth and have contributed to the greenhouse effect. 

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