Chlorofluorocarbon solvents Freon

Solvents, like contaminants, may be polar or nonpolar. As a general rule, polar solvents dissolve polar residues while nonpolar solvents dissolve nonpolar residues. Thus, ionic residues such as chlorides, salts, acids, acid fluxes, and alkalis are best dissolved and removed with polar solvents such as water, isopropyl alcohol, ethanol, or methylethyl ketone. Greases, oils, silicones, rosin flux, and low-molecular-weight monomers are best dissolved and removed with solvents such as hydrocarbons, Freons , hydrochloro-fluorocarbons, xylene, terpenes, and naphtha. To remove both polar and nonpolar residues, a two-step process using both types of solvents may be used or, more conveniently, an azeotrope mixture of the two solvents can be used in a one-step process. Most of the chlorofluorocarbon solvents (Freons ) and their azeotropes with alcohols, methylene chloride, or ketones are being phased out due to their high ozone-depletion potentials. Solvent blends and azeotropes of hydro-fluoroethers and hydrochlorofluorocarbons (HCFC) are now replacing these solvents. 

A generic name for a group of chlorofluorocarbons used as refrigerants, propellants, and solvents. Freon-12 is CF2C12, and Freon-22 is CHC1F2. (p. 221)... 

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. 

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]. 

In recent years, many of the technologically outdated methods of 40 CFR Part 136 have been upgraded to incorporate the latest advances in instrumental analysis. For example, capillary chromatographic columns with superior compound resolution replaced obsolete packed columns in gas chromatography (GC) and GC/MS analytical methods Freon 113, a chlorofluorocarbon harmful to the environment, was phased out as the extraction solvent in oil and grease analysis and replaced with hexane in Method 1664 (EPA, 1999b). 

The radical that appeared to meet the criteria for X most closely was (CF3)2NO and the desired solvent properties were most closely met by some of the Freons (chlorofluorocarbons). The radical was generated photochemically via reactions... 

Chlorofluorocarbons (CFCs) are chemically inert, nonflammable, nontoxic compounds that are superb solvents and have been used in many industrial processes they are excellent coolants for air conditioners and refrigerators. Two CFCs that have been widely used are Freon-11 and Freon-12 (Freon is a DuPont trade name). 

Strong circumstantial evidence implicates synthetic chlorofluorocarbons (CFCs) as a major cause for ozone depletion. These gases, known commercially as Freons, have been extensively used as cooling fluids in refrigerators and in home and automobile air conditioners, in industrial cleaning solvents, and in the manufacture of some plastic foams. They were once widely used as propellants in aerosol spray cans because of their odorless, nontoxic, and nonflammable properties and because they are chemically inert (Scheme 4.62). 

CFC Phaseout Requirements. The solvent selected for use in the degreasing tank operation is listed as a designated chlorofluorocarbon, the use of which was subjected to the phaseout requirements stipulated under the Clean Air Act of 1990. Since this system is still in the design phase, it is not too late to consider an alternate degreasing solvent that is not a threat to the earth s ozone layer. Note While it is true that the use of Freon 113 is not a particular hazard to personnel or the equipment used in this degreasing process, its use still poses an alleged threat to the earth s environment and, therefore, its identification as a potential hazard is warranted.)... 

The halogenated hydrocarbons are a related class of compounds. These are hydrocarbons, including alkanes, in which one or more of the hydrogen atoms have been replaced by some halogen — normally chlorine or bromine. Halogen substituents are named as chloro-, bromo-, and so on. Members of this class of compound include chloroform, once used as an anesthetic carbon tetrachloride, used at one time in dry cleaning solvent and freons (chlorofluorocarbons, CFCs), elements that have played a major role in the depletion of the ozone layer. See Chapter 18 for a discussion of CFCs and ozone. 

Production of chlorofluoromethanes (and of chlorofluo-roethanes) called chlorofluorocarbons (CFCs) or freons began in 1930. These compounds have been used as refrigerants, solvents, and propellants in aerosol cans. 

There have been a number of subsitutions of chemicals in recent years, many of them driven by environmental concerns and regulations resulting from those concerns. One of the greater of these has been the substitution of hydrochloro-fluorocarbons (HCFCs) and hydrofluorocarbons (MFCs) for chlorofluorocarbons (Freons or CFCs) driven by concerns over stratospheric ozone depletion. Substitutions of nonhalogenated solvents, supercritical fluid carbon dioxide, and even water with appropriate additives for chlorinated hydrocarbon solvents will continue as environmental concerns over these solvents increase. 

Several different solvents have been used. These include petroleum ether, diethyl ether, chloroform, and carbon tetrachloride. Of these, petroleum ether and diethyl ether are highly flammable, whereas chloroform (although a very good solvent) and carbon tetrachloride are toxic. Thus, these solvents are not recommended for use. Currently, 1,1,2 trichloro, trifluoroethane (Freon 113) is used when infrared (IR) absorbance is used for analysis. However, these solvents are being phased out because of potential interference with the ozone layer in the atmosphere. Studies are currently under way to find a replacement solvent. Potential candidates include hexane, cyclohexane, methylene chloride, perchloroethylene, and a commercial hydro chlorofluorocarbon (DuPont 123). When the gravimetric technique is used for analysis, 1,1,1-trichloroethane or dichloroethylene may also be used. 

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