Chloro-fluorocarbons

Entries on new materials, including re-cyclate plastics, fullerenes, hard-surfaced polymers, dendrimers, transflective materials, rapid prototyping materials, silicone nitride, supercritical fluids, bulk molding compounds, conversion coatings, folic acid, replacements for chloro-fluorocarbons ... 

Soon, as Midgley put it, Everything looked right. Within a few hours, they had identified a whole new class of potential compounds the chloro-fluorocarbons, later nicknamed CFC s, and trademarked Freon by Du Pont. 

Sudden deaths from sniffing aerosols have been associated with a number of chloro-fluorocarbons. The deaths are thought to be due to ventricular fibrillation following cardiac sensitization. ... 

Oxides, halides and oxide halides of a variety of metals are used as catalysts for disproportionation reactions. The choice of catalyst depends on the reaction conditions and the chloro-fluorocarbons used for disproportionation. Table 1 lists the principal compounds. 

Apart from these synthetically impractical examples of hydrolysis of chloro-fluorocarbons, there are useful applications converting some chlorofluorocarbons to fluonnated carboxylic acids. As an alternative to the use of the highly corrosive fuming sulfuric acid, normally used in batch processes, a continuous hydrolytic process for converting 1,1,1-trichlorotrifluoroethane (CFC-113a), available by isomerization of CFC-113 [44], to trifluoroacetic acid has been developed [45] (equation 45). It uses metal chloride catalysts deposited on high-surface-area supports Unreacted CFC-113a can be recycled. 

In this way an equilibrium is maintained between the three forms of oxygen, O, 02 and 03. This equilibrium can be upset by chemical species which are carried to the upper atmosphere, specifically nitrogen oxides and chloro-fluorocarbons. 

Z. Ainbinder, L.E. Manzer, M.J. Nappa, Catalytic routes to hydro (chloro) fluorocarbons, Environ. Catal. (1999) 197-212. 

Since the introduction of metered-dose inhalers, nasal solutions have increasingly been formulated as nasal sprays. Initially, aerosol-based systems containing chloro-fluorocarbons were employed however, the Montreal Protocol put an end to this. Thereafter, mechanical pumps or actuators were employed to deliver nasal formulations as sprays. These devices, using actuators, can precisely deliver as little as 25 pL and as much as 200 pL of a formulation. However, various factors must be considered in formulating the spray these include viscosity, particle size, and surface tension, all of which may affect the accuracy of the dose administered. 

Specific product orientation L. E. Manzer and V. N. M. Rao describe catalytic pathways to the modern product challenge of alternatives to chloro-fluorocarbons. 

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). 

Although hydrocarbon aerosol propellants are relatively inexpensive, nontoxic, and environmentally friendly (since they are not damaging to the ozone layer and are not greenhouse gases), their use is limited by their flammability. While hydrocarbon propellants are primarily used in topical aerosol formulations, it is possible that butane may also be useful in metered-dose inhalers as a replacement for chloro-fluorocarbons. 

The global presence of radioactive fallout from the nuclear bomb tests of the 1950s and 1960s clearly illustrated the capacity of the atmosphere to distribute chemicals around Earth. Global transport has been demonstrated for a large number of chemicals that do not rapidly degrade or settle out of the atmosphere. Examples are methane (CH4), nitrous oxide (N20), and chloro-fluorocarbons (CFCs), all of which have half-lives in the atmosphere ranging from years to decades. 

Exposure to 2,2-dichloro-l,l,l-trifluoroethane (HCFC-123) produces reversible liver lesions in laboratory animals. When exposure to HCFC-123 was coupled with ethanol ingestion, liver toxicity was markedly increased. The increase, due to CPY2E1 induction, greatly enhanced the metabolism of HCFC-123 to compounds that are toxic to the liver. 14 HCFC-123 is a widely used substitute for banned ozone-depleting chloro-fluorocarbons. This study strongly suggests that exposure to HCFC-123 can lead to toxic end points in individuals who chronically consume ethanol. 

See fluorocarbon. Note Many types contain chlorine, as well as fluorine, and should be called chloro-fluorocarbons. 

The discovery of the ECD dates back to a sensitive anemometer based on ions generated from a radioactive source made from radium extracted from the luminous dials of discarded aircraft instruments. This device was very sensitive but its response was perturbed by cigarette smoke. This was a drawback in the device and to discover its source, other compounds, such as halocarbons were tested. However, in 1948, this was something to merely note for the future. Looking back I realized that the key to invention is need. We did not at that time need a device to detect low levels of chloro-fluorocarbons and so the electron capture detector was in a sense prematurely invented. [2]... 

Dimethyl ether has been increasingly used as a propellant in aerosol formulations to replace chloro-fluorocarbons, which are found to destroy the ozone layer of the atmosphere. Dimethyl ether is nontoxic and easily degrades in the troposphere. Although about 90% of the major current U.S. aerosol industry uses hydrocarbon-based propellants (mostly isobutane and propane), DME could become a more widely used propellant in the coming years. Several aerosol-based... 

Methane is not as important as C02 in the greenhouse effect since the C02 percentage is much greater in the earth s atmosphere. Chloro-fluorocarbons (CFCs) are even more effective greenhouse gases, but are only about 20% of the C02 greenhouse gases. They are involved in the destruction of stratospheric ozone. 

The biggest use of carbon tetrachloride (90%) is the production of chloro-fluorocarbons (CFCs) [144], Carbon tetrachloride reacts with hydrogen fluoride to produce freon ... 

Nature cannot be subjected to increasing concentrations of man-made substances that natural systems will not purge. Example The emissions of pesticides, PCBs, mercury, chloro-fluorocarbons, mine wastes, and innumerable other toxics and cancer-causing substances have contaminated food supplies, drinking water, ecosystems, and every human body on the planet. 

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