Hydro fluorocarbons

Zero-ODP alternatives are the substitutes of choice in many foam-manufacturing applications. However, the use of HCFCs is sometimes necessary in order to meet some product specifications. The viability of liquid hydro fluorocarbon (HFC) isomers in this industry remains to be proved, and hydrocarbon alternatives need to be better qualified, as well. 

K. Kobuch, D.H. Menz, H. Hoerauf, J.H. Dresp, V.P. Gabel, New substances for intraocular tamponades Perfluorocarbon liquids, hydrofluorocarbon liquids and hydro-fluorocarbon-oligomers in vitreoretinal surgery, Graefes Arch. Clin. Exp. Ophthalmol. 239 (2001) 635-642. 

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. 

Carbon dioxide is, by far, the most attractive SCF for many reasons It is inexpensive and abundant at high purity (food grade) worldwide and it is nonflammable, non-toxic, and environment friendly moreover, its critical temperature T = 31 °C) permits operations at near-ambient temperature which avoids product alteration and its critical pressure (= 74 bar) leads to acceptable operation pressure, generally between 100 and 350 bar. In fact, supercritical carbon dioxide behaves as a rather weak nonpolar solvent, but its solvent power and polarity can be significantly increased by adding a polar cosolvent that is chosen among alcohols, esters, and ketones. Ethanol is often preferred because it is not hazardous to the environment, not very toxic, and available pure at low cost. Hydro fluorocarbons (HFCs) are very costly and their specific properties rarely justify their use in the replacement of carbon dioxide. 

On the other hand, Pd catalysts were used, with good results, for the partial dehalogenation of chloro-fluorocarbons to hydro fluorocarbons [9-11], and of chlorobenzenes [12], but at present there are few studies on chlorinated aliphatic substrates like CCI4. 

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. 

Governments have tackled the problem, and most industrialised countries have now banned the use of CFCs. Chemists developed new compounds for fridges and aerosols, such as hydro fluorocarbons (HFCs) for example, CHjFCFj. These non-chlorinated compounds break down more quickly once released into the air because of the presence of hydrogen in their molecules, so they never rise in the atmosphere as far as the ozone layer. There are now signs that the ozone layer is recovering from the effects of CFCs. The hole in the ozone layer is very slowly closing up. 

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." ... 

The interest in catalyst recyclability has led to the development of biphasic catalysts for hydro-boration.22 Derivitization of Wilkinson s catalyst with fluorocarbon ponytails affords [Rh(P (CH2)2(CF2)5CF3 3)3Cl] which catalyzes FIBcat addition to norbornene in a mixture of C6FnCF3 and tetrahydrofuran (TF1F) or toluene (alternatively a nonsolvent system can be used with just the fluorocarbon and norbornene) to give exo-norborneol in 76% yield with a turnover number up to 8,500 (Scheme 4). Mono-, di- and trisubstituted alkenes can all be reacted under these conditions. The catalyst can be readily recycled over three runs with no loss of activity.23... 

Table 12. Toxicities of Various Hydro-/Ch1oro-/Fluorocarbons... 

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

The Ru-red or Ru-brown complex adsorbed in the Nafion membrane is probably present in a microheterogeneous environment imposed by hydro-phobic cluster made of fluorocarbon moiety and by hydrophilic cluster made of sulfonate ions, and the Ru-red or Ru-brown is electrostatically held by the sulfonate ions. In a polymer membrane, the metal complex molecules would be isolated and the microheterogeneous environment would alter the complex-solvent interaction. Such effects are well characterized for macromolecular metal complexes . Since Ru-red and Ru-brown water oxidation catalysts are strong oxidants in their higher oxidation states, they would attack organic ligands of the... 

Pineri et al have performed a series of investi-gations " " " on the structural properties of Nafion polymers and have derived a three-phase model in which fluorocarbon crystallites, ionic hydrophilic clusters, and an amorphous hydro-phobic region of lower ionic content coexist. The microcrystallites can be eliminated by heating the Nafion-Na sample to 330°C, and then quenching it to room temperature." They showed that at high water content (>15wt%) the quenched Nafion membranes are essentially two-phase systems." These phases are rather well separated and most of the water is in the ionic clusters. Samples of lower water content (8 wt %) show deviations from two-phase behavior." ... 

These hydro endcapped liquids (V, n = 1-7) were commercialized by DuPont as the Freon E series fluorocarbons for use as stable fluids, heat-transfer liquids, and dielectric coolants. The acyl fluorides were also converted into inert materials by dimerization with loss of the carbonyl group either electrochemically or photoche-mically (Eq 13.8). Both processes were used to make dimers and mixed dimers to tailor the boiling point of the flnal products. 

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. 

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