Chlorofluorocarbons aerosol propellant

TSCA also placed restrictions on the use of chlorofluorocarbons, asbestos, and fuUy halogenated chlorofluoroalkanes such as aerosol propellants. 

During the 1980s, it became recognized that chlorofluorocarbons (CFCs), widely used as aerosol propellants, are damaging the ozone layer, and aerosol manufacturers were asked to use other propellants. Some... 

The production of chlorofluoro- and hydrochlorofluorocarbons expanded rapidly after 1945, reaching about 1 milbon tons in 1986 despite a drop m production in the late 1970s, when the United States and several other countnes banned the use of chlorofluorocarbons as aerosol propellants In the early 1990s, production and consumpaon are in decline... 

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. 

Ban on chlorofluorocarbons (CFCs) as aerosol propellants react with ozone in the stratosphere, causing an increase in the penetration of ultraviolet sunhght and increase the risk of skin cancer. 

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). 

Freon is a commercial trademark for a series of fluorocarbon products used in refrigeration and air-conditioning equipment, as aerosol propellants, blowing agents, fire extinguishing agents, and cleaning fluids and solvents. Many types contain chlorine as well as fluorine, and should be called chlorofluorocarbons (CFCs) [85,86]. 

Specific bans on chemicals or uses have not been the most important outcome of TSCA. Only one type of chemical, PCBs, was specifically targeted in the original law and they are now outlawed in most of their uses. EPA administration of the law in its early years led to a ban of chlorofluorocarbons as aerosol propellants, restrictions on dioxin waste disposal, rules on asbestos use, and testing rules on chlorinated solvents. It has led to a central bank of information on existing commercial chemicals, procedures for further testing of hazardous chemicals, and detailed permit requirements for submission of proposed new commercial chemicals. 

Currently, the major application of DME is as an aerosol propellant, for example in hairsprays and paintsprays, where it has replaced the formerly used ozone-destroying chlorofluorocarbons (CFCs). 

Third, even where it is clear that a particular type of chemical has caused a particular incident of damage, and we can identify who was causally responsible for the existence of that chemical (if not necessarily its presence in a particular location), the first condition, that the conduct transgressed a norm, is often not met. This is because those norms require only that foreseeable consequences are taken into account one is not responsible for consequences that could not have been foreseen. Thus Du Pont, the main manufacturer of chlorofluorocarbons (CFCs) — non-toxic and non-flammable chemicals that were used as a refrigerant and aerosol propellant for many decades — have not been held to account for the hole in the ozone layer caused by those chemicals because at the time the key decisions to manufacture them were made, in the 1930s, these effects could not have been predicted (Colborn et al, 1996, pp243-245). 

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. 

A number of compressed and liquified gases are used as refrigerants and aerosol propellants. These include nitrous oxide, nitrogen, carbon dioxide, propane, and butane. The use of chlorofluorocarbons (CFCs) is restricted because of environmental pollution leading to health hazards. These have been replaced by hydrogenated fluorocarbons (HFCs), which are less likely to cause environmental pollution. 

Chlorofluorocarbons (CFCs) A family of inert, nontoxic, and easily liquefied chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents and aerosol propellants. Because CFCs are not destroyed in the lower atmosphere, they drift into the upper atmosphere where their chlorine components destroy the ozone. 

Chlorofluorocarbon 12, a freon, was used in refrigeration systems and air conditioners and as an aerosol propellant because of its high stability and low toxicity. Its stability results in environmental problems. It does not decompose until it reaches the upper atmosphere, where ultraviolet light causes the carbon-chlorine bonds to break.The resulting chlorine atoms catalyze the destruction of ozone, resulting in the infamous ozone hole.The use of this and other stable freons has recently been phased out. 

Chlorofluorocarbons such as CFC13 and CF2a2, used as foam-blowing agents, aerosol propellants, and refrigerants, are photochemically decomposed to give Cl atoms, and these catalyze ozone decomposition22 via the mechanism... 

Trichlorofluoromethane is a member of a class of molecules called chlorofluorocarbons or CFCs, which contain one or two carbon atoms and several halogens. Trichlorofluoromethane is an unusual organic molecule in that it contains no hydrogen atoms. Because it has a low molecular weight and is easily vaporized, trichlorofluoromethane has been used as an aerosol propellant and refrigerant. It and other CFCs have been implicated in the destruction of the stratospheric ozone layer, as is discussed in Chapter 15. 

Chlorofluorocarbons (Sections 7.4, 15.9) Synthetic alkyl halides having the general molecular formula CFjrCl4 jt. Chlorofluorocarbons, abbreviated as CFCs, were used as refrigerants and aerosol propellants and contribute to the destruction of the ozone layer. 

Pharmaceutical inhalation aerosols are widely used for treatment of diseases such as asthma and chronic bronchitis. There are three basic types of aerosol products the propellant-driven metered-dose inhalers, the dry powder inhalers, and the nebulizers. Because of the ozone-depleting and greenhouse effects of the chlorofluorocarbon (CFG) propellants, interest in the dry powder aerosols has risen in recent years. 

Pulmonary delivery of drugs is the administration route of choice in respiratory diseases such as chronic obstructive pulmonary disease and asthma. Different devices are available, including metered-dose inhalers, dry powder inhalers, and nebulizers, and nearly 80% of asthmatic patients worldwide use metered dose inhalers (1). Chlorofluorocarbons have been used as an aerosol propellant in metered-dose inhalers however, they deplete the ozone layer and are being replaced by more environment-friendly propellants, even though the contribution of aerosols of this type to the total global burden of chlorofluorocarbons is less than 0.5%. The first chloro-fluorocarbon-free metered-dose inhaler for asthma treatment was approved by the FDA in 1996 (2) and the European Union has set 2005 as a target date for the withdrawal of all chlorofluorocarbon-based inhalers (1). In the USA, prescriptions for chlorofluorocarbon-free medications rose from 16.4 million in 1996 to 33.8 million in 2000 (2). Most of the chlorofluorocarbon-free medications were steroids for nasal use (27.2 million). However, chlorofluorocarbon-containing medications stiU represented two-thirds of all prescriptions and increased from 63.0 to 67.6 million dispensed (2). 

For a discussion of the numerical nomenclature applied to this aerosol propellant, see Chlorofluorocarbons. 

Dichlorodifluoromethane, dichlorotetrafluoroethane, and trichloromonofluoromethane are chlorofluorocarbon (CFC) aerosol propellants used in pharmaceutical formulations. 

Dichlorodifluoromethane is used as an aerosol propellant in metered-dose inhaler (MDI) formulations, either as the sole propellant or in combination with dichlorotetrafluoroethane, trichloromonofluoromethane, or mixtures of these chlorofluorocarbons. Dichlorodifluoromethane may also be used as a propellant in an aerosolized sterile talc used for intrapleural administration and is also used alone in some MDIs containing a steroid. 

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