Perfluorocarbons, preparation

Polymer Solvent. Sulfolane is a solvent for a variety of polymers, including polyacrylonitrile (PAN), poly(vinyhdene cyanide), poly(vinyl chloride) (PVC), poly(vinyl fluoride), and polysulfones (124—129). Sulfolane solutions of PAN, poly(vinyhdene cyanide), and PVC have been patented for fiber-spinning processes, in which the relatively low solution viscosity, good thermal stabiUty, and comparatively low solvent toxicity of sulfolane are advantageous. Powdered perfluorocarbon copolymers bearing sulfo or carboxy groups have been prepared by precipitation from sulfolane solution with toluene at temperatures below 300°C. Particle sizes of 0.5—100 p.m result. 

The preparation of perfluorinated compounds is largely based on the exhaustive fluorination of the corresponding hydrocarbon species and three synthetic procedures have been widely used. Two of these processes, electrochemical fluorination [27] (ECF), successfully used for the preparation of perfluoroacids (3M), and fluorination by high valent metal fluorides [28] such as cobalt trifluoride (itself prepared from cobalt difluoride and fluorine), used for the preparation of perfluorocarbons (Flutec fluids, BNFL), have been reviewed elsewhere. The third major process for the preparation of perfluorinated compounds involves direct fluorination. 

In addition analogous monofunctional and difunctional perfluorocarbon products containing multiple ether linkages may be routinely prepared on multikilogram scales in very high yield.20... 

Perfluorocarbons. In 1966, it was demonstrated (27) that a laboratory mouse could survive total immersion in a perfluorochemical (PFC) solution. This material, similar to commercial Teflon, is almost completely inert and is insoluble in water. A water-soluble emulsion was prepared that could be mixed with blood (28), and in 1968 (29) the blood volume in rats was completely replaced with an emulsion of perfluorotributylamine [311-89-7], C12F27N. The animals survived in an atmosphere of 90—100% 02 and went on to long-term recovery. However, the 02 content of the perfluorochemicals has a linear dependence on the partial pressure of oxygen, P, as can be seen in Figure 1. The very high 02 tension required to transport physiologic amounts of 02 (12) and the propensity of the perfluorocarbon to be taken up by the reticuloendothelial cells were considered to be severe limitations to the development of clinically useful perfluorocarbon blood substitutes (30). 

Liquid fluorocarbon was used as continuous phase by Perez-Moral and Mayes [19] as well. They proposed a new method for rapid synthesis of MIP beads, in that they prepared 36 polymers imprinted for propranolol and morphine with different amounts of EDMA as a cross-linker and different functional monomers (MAA, acrylic acid, hydroxyethyl methacrylate, 4-vinylpyridine) directly in SPE cartridges. The properties of MIP microspheres prepared by this method were very similar in terms of size, morphology and extent of rebinding to microspheres prepared by conventional suspension polymerisation in perfluorocarbons as well as to bulk polymers prepared in the same solvent. The most notable advantages of this method are no waste production (no transfer of beads during washing steps) and possible direct use for a variety of screening, evaluation and optimisation experiments. 

One of the technically and commercially most important cation-exchange membranes developed in recent years is based on perfluorocarbon polymers. Membranes of this type have extreme chemical and thermal stability and they are the key component in the chlorine-alkaline electrolysis as well as in most of today s fuel cells. They are prepared by copolymerization of tetrafluoroethylene with perfluorovinylether having a carboxylic or sulfonic acid group at the end of a side chain. There are several variations of a general basic structure commercially available today [11]. The various preparation techniques are described in detail in the patent literature. 

Because the supply exceeds demand, the HCI generated often cannot be sold or reused even after purification. Although electrochemical fluorinations have been practiced commercially for many years, the main products of the reactions are typically perfluorocarbons since C-H bonds rarely survive. New methods, which avoid the need to feed chlorine and disposal of HCI are needed to prepare HCFCs and HFCs are obviously desirable. 

Another potential application of perfluorocarbons is their use as bulking agents where the volume of conventional solvent is reduced by replacement with a perfluorocarbon. Although the halex reaction is a successful industrial process, there are problems recovering the toxic dipolar aprotic solvents. Chambers [80] has shown that, on a preparative scale, up to 75% of the sulfolane can be replaced in the halex reaction by an equivalent volume of perfluorohydrophenanthrene (b. pt. = 215°C). On cooling the reaction mixture, it is a simple matter to separate off the fluorous solvent at the end of the reaction for recycling. 

Although perfluorocarbons are extremely thermally stable compounds, pyrolysis at elevated temperatures can lead to useful preparations of some simple alkenes [20] (Figure 7.6). 

Hammerschmidt, D.E. Vercellotti, G.M. Limitation of complement activation by perfluorocarbon emulsions superiority of lecithin-emulsified preparations. Biomat. Artif Cells Artif Organs 1988, 16, 431 38. 

Oxygen carriers can be divided into two classes hemoglobin-based oxygen carriers, prepared from hemoglobin of human or bovine origin, and synthetic perfluorocarbons. 

Interest in the use of reducing agents to activate C-F bonds was revived when systems that enabled selective removal of fluoride from perfluorocarbons were discovered in contrast to the complete (destructive) removal of halides as in sodium fusion reactions employed in methods for halogen analysis [31]. (Interest in this latter area has also had resurgence in the search for methods capable of destroying chlorofluorocarbons [32].) The key breakthrough was the report by MacNicol and Robertson that hexakis(thiophenoxy)napthalene can be prepared by treatment of perfluorodecalin with excess sodium phenylthiolate for 10 days at 70°C in DMF [33]. 

Ultraviolet irradiation of perfluorocarbons in the presence of (C5Me5)2Fe and Li03SCF3 as a fluoride acceptor provides an exceptionally mild system [80] to prepare perfluoroalkenes from perfluoroalkanes and the chemistry can be made catalytic with respect to iron by using zinc to reduce [(C5Me5)2Fe]+(Scheme 6). 

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