Hydro chlorofluorocarbons

Tuazon, E. C., and R. Atkinson, Tropospheric Reaction Products and Mechanisms of the Hydrochlorofluorocarbon-141b, Hydro-chlorofluorocarbon-142b, Hydrochlorofluorocarbon-225ca, and Hydrochlorofluorocarbon-225cb, Enriron. Sci. Technol., 28, 2306-2313 (1994). 

The impact of deposition on global distribution has been noted for the CFC replacements hydro-chlorofluorocarbons (HCFCs), the chlorinated solvents tetrachloroethene (PCE), and trichloro-ethene (TCE), as these compounds undergo gas phase oxidation and photochemical degradation, resulting in the formation of carbonyl halides (e.g., CCI2O) and haloacetyl halides (e.g., bromo-, chloro-, and fluoroacetates). As these compounds are polar and water soluble, they are transported via aerosols, rain, and fog, which impacts their tropospheric lifetime and depositional fluxes (Rompp et al., 2001 de Bmyn et al., 1995). It is not clear whether and to what extent there is evidence of latitudinal fractionation of these compounds. 

Scheme 2.14 Lewis acid-assisted halogen exchange of chloroalkanes to (hydro)chlorofluorocarbons (CFC and HCFC).

The production of many solvents traditionally used to clean for oxygen service is being phased out. The cost of these solvents and their disposal is rapidly increasing as a result. However, many new solvents are being developed specifically for cleaning and are becoming commercially available. These include terpenes, aliphatic hydrocarbons, alcohols, esters, hydro-chlorofluorocarbons, hydrofluorocarbons, and silicone-based solvents. Solvents must be tested for material compatibility, particularly with regard to any polymer components in the equipment to be cleaned. 

While less harmful to the environment than CFCs, hydro-chlorofluorocarbons (HCFCs) are stiU ozone-depleting (they are classified as Class II ozone-depleters) and will be phased out by 2020. Hydrofluorocarbons appear to have little or no ozone-depleting effect and are replacing CFCs and HCFCs in refrigerants and aerosol propellants. 

In order to enable the fast discontinuation of the production and use of fully halogenated CFCs, hydro-chlorofluorocarbons were introduced in industry as a transition stage. The atmospheric fate and impact of these hydrochlorofluorocarbons and chlorinated solvents are described in [387]. The authors come to the conclusion, that these compounds, with the exception of 1,1,1-trichIoroethane, make a small or insignificant contribution to the stratospheric ozone depletion, global warming, photochemical smog , acid rain or chloride and fluoride levels in precipitations. The ozone depletion potentials are 10 to 50 times lower than that of CFCll or CFC12, mainly as a consequence of their shorter atmospheric lifetime—some months to 10 years—due to destruction in the atmosphere. 

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. 

States would spend 160 billion per year on pollution control. In 1996 Ben Lieberman, an environmental research associate with the Competitive Enterprise Institute, estimated that in the United States the cost of the phaseout of chlorofluorocarbons (CFCs) in accordance with the 1987 Montreal Protocol on Substances That Deplete the Ozone Layer could reach 100 billion over the next ten years. Indeed chemical manufacturers had to develop eco-friendly substitutes such as hydrochlorofluorocarbon (HCFC) and hydro-fluorocarbon (HFC), which are more costly to make, and hundreds of millions of pieces of air-conditioning and refrigeration equipment using CFCs had to be discarded. 

Pbarmaceutical PropeUants Many inhaled medications used to treat asthma contained chlorofluorocarbon (CFC). However, the Montreal Protocol called for a ban ofCFCs as a propellant in pharmaceutical products by 2008. Two hydro-fluoroalkanes (HFAs) appear to be effective in delivering asthma medications to the lungs. However, the medication dosage had to be cut in half with the new HFA propellents. 

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. 

The replacement of chlorofluorocarbons (CFC) with environmentally more benign chemicals, as recently mandated by the Montreal Protocol and subsequent revisions, has caused a reduction of the insulation efficiency of the PU foams, since the new blowing agents available, like hydrocarbons, hydro-fluorocarbons (HFC) or carbon dioxide have worse gas thermal conductivity properties. 

Stones are protected from deleterious effects of water and pollution by application of amorphous fluoropolymer solution." Solvent is selected from the group consisting of acetone, methyl-ethyl ketone, ethyl acetate, t-butyl acetate, hydrochlorofluorocarbons, chlorofluorocarbons, hydro fluorocarbons and perfluorocarbons." Another method uses epoxy-modified silane in hydrophilic solvent." ... 

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