Freons and Halons

The (now nearly discontinued) low-molecular-weight, hydrogen-free, so-called chlo-rofluorocarbons (CFCs or freons) are manufactured by the reaction between HF and tetrachloromethane [carbon tetrachloride (CCI4)] in the presence of antimony pentachloride (SbCls) (Equation 7.2). 

Apparently, since their development in the early 1930s by the E.I. duPont Company, the increasing use of these materials has proved to be deleterious to the ozone (O3) present in the upper atmosphere. It is now widely held that the photochemical destruction of the CFCs results in the production of chlorine atoms (-Cl) and chlorofluoromethyl radicals (e.g., CCIF2) (Equation 7.3) and the former, among 

Other reactions, interacts with ozone (O3), to produce chlorine monoxide (CIO) and oxygen (O2) (Equation 7.4). 

A wide search for alternative materials has resulted in the duPont Company suggesting that CFCs be replaced by hydrochlorofluorocarbons (HCFCs) (Equation 7.5). 

When a chlorine ( Cl) or fluorine ( F) in the CFC is replaced by a hydrogen, HCFCs result. Reports of widespread testing of HCFCs appear to indicate that their decomposition in the lower atmosphere will preserve the upper atmosphere ozone (O3). Of course, full-scale use of HCFCs may have unforeseen 

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D. Freons and halons may produce potent irritant gases and vapors (eg, phosgene, hydrochloric acid, hydrofluoric acid, and carbonyl fluoride) when heated to high temperatures, as might happen in a fire or if a refrigeration line Is cut by a welding torch or electric arc. 

Professor of Clinical Medicine, University of California, San Francisco dennis itsa.ucsf.edu Section II Freons and Halons... 

Research continues to find suitable replacements for both groups (Freons and Halons) of materials, which, given what will inevitably be worldwide use, will be benign or, at least, less deleterious to the environment than our previous choices. 

Continuing dissatisfaction amongst fluorine chemists with the cumbersome alphanumeric ASHRAE ( Freon ) codes for fluorocarbons (which contain no provision for branched-chain compounds) has led to interesting proposals recently concerning alternative codes for HFCs and HFEs.10 To be fair to ASHRAE. when its predecessor, ASRE, standardized the so-called Du Pont code in the late 1950s, no one could have foreseen the proliferation of lists of volatile fluorocarbons (and hence coded designations) arising from the impressive commercial drive to locate environmentally acceptable in-kind replacements for C.FCs and Halons.8... 

Trichloroethylene and 1,1,1-trichloroethane are used in correction fluids, dry-cleaning products, degreasing sprays, and solvents and spot removers. Bromochlorodifluoro-methane is a compound found in halon fire extinguishers that is abused. Freon is used for refrigeration and air conditioning systems. Anesthetics include halothane, chloroform, and the local anesthetic ethyl chloride. Methylene chloride is a component of rubber cement, paint strippers, and degreasing agents, and fluorocarbons are present in many types of aerosol sprays. 

Trlfluorobromomefhane (Halon 1301 Freon 13B1 [CAS 75-63-8]) Extremely high air levels (150,000-200,000) can cause CNS depression and cardiac arrhythmias. See also p 209. 1000 ppm 40,000 ppm Colorless gas with a weak ether-like odor at high levels and poor warning properties. Not combustible. 

The discovery of the harmful effect of CFCs on stratospheric ozone resulted in the elimination of CFCs from aerosol spray cans (with the exception of essential medical uses such as asthma inhalers) and refrigeration systems. It was also discovered that similar bromine-containing compounds called halons that were used in fire extinguishers posed the same threat as Freon. 

Chlorofluorocarbons (CFCs), such as dichlorodifluoromethane, commonly called Freons, are volatile 1- and 2-carbon compounds that contain Cl and F bonded to carbon. These compounds are notably stable and nontoxic. They were widely used in recent decades in the fabrication of flexible and rigid foams and as fluids for refrigeration and air conditioning. A related class of compounds, the halons, such as CBrClF2 (Halon-1211), are used in fire extinguisher systems particularly on aircraft. 

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