Stephan Rüdiger

Persistent fluorocarbon radicals generated by elemental and electrochemical fluorination

Abstract Stable fluorocarbon radicals ware obtained by fluorination of branched fluoro-olefins and unsaturated partially fluorinated tertiary amines. As a fluorine source, elemental fluorine as well as the electrochemical fluorination process (ECF) in anhydrous hydrogen fluoride (AHF) were used. The persistent radicals were investigated by ESR spectroscopy concerning their structure and stability. ECF-generated fluorocarbon radicals give some evidence of intermediately formed atomic fluorine as a key factor of the AHF-based electrochemical process. These findings favour and electrofluorination mechanism similar to that of elemental fluorine. Because of their unusual stability, the radicals can be used as spin markers and to obtain 2D images by using an ESR tomographic technique. Stabilized with emulsifiers, they form stable aqueous emulsions.

On reactions of carbon disulfide induced by “naked” fluoride Part 3. Cyclization of carbon disulfide

Abstract The tetramethylammonium salt of trithiocarbonic acid 3,5-dithione-1,2-dithiol-4-yl (1) is formed upon reaction of CS 2 with tetramethylammonium fluoride (TMAF) in dimethylformamide (DMF), probably via intermediate formation of FCS - 2 . The crystal structure of 1 was determinated by X-ray structural analysis.

Methods for forecasting the usefulness of perfluorocarbons for blood substitutes

Abstract It is shown that the development of more efficient perfluorocarbon (PFC) emulsions for blood substitution depends mainly on the application of improved PFCs, the most important PFC-properties being emulsion stability and excretion rate. As a basis for synthesis strategy the estimation of the latter, from the structural formulas alone, has already been reported. for the prediction of the emulsion stability, quantitative structure-stability relationships of several PFCs have now been investigated. It was found that the molar volumes of the PFCs, estimated by means of Lawsons group additivity system, correlate well with their emulsion stability (high molar volume corresponds to high emulsion stability). These findings support Ostwald-ripening as being the main process of PFC-emulsion deterioration.

Studies on the conversion of 1,1,1-trichlorotrifluoroethane, chloro-2,2,2-trifluoroethane, and 1,1,1-trifluoroethane by catalytic oxidation, hydrolysis and ammonolysis

Catalytic hydrolysis and ammonolysis of CF3CCl3 (CFC-113a) and CF3CH2Cl (HCFC-133a) and oxidation of CF3CH3 (HFC-143a) were studied as possible routes to produce trifluoroacetic acid (TFA), trifluoroethanol (TFE) or trifluoroethylamine (TFEA), respectively. Catalysts employed in this study included oxides/halides of Fe, Pd, Cs, Cu, Sn, supported on carbon, Al2O3, ZrO2, TiO2, sulfated zirconia and fluoride supports like β-AlF3, and MgF2, as well as modified lanthanum phosphates. The reaction temperatures were varied from 100 to 450 °C, under these conditions CF3CCl3 and CF3CH2Cl could be hydrolysed giving trifluoroacetic acid or trifluoroethanol, respectively, in moderate yields, however all other reactions yielded predominantly CF2CHCl. Optimum conditions were identified for obtaining TFA over Fe/C catalyst by hydrolysis of CFC-113a, and for TFE by hydrolysis of HCFC-133a over alkaline modified lanthanum phosphate.

On reactions of carbon disulphide induced by ‘naked’ fluoride Part 2: Reactions with 2-H-heptafluoropropane, hexafluoropropene, and bis (2,2,2-trifluoroethyl) amine

Abstract The reaction of CS 2 and tetramethylammonium fluoride (TMAF) with 2- H -heptafluoropropane (R227) leads to 2,4-bis(hexafluoroisopropylidene)-1,3-dithietane as well as to the tetramethylammonium salt of heptafluorodithioisobutyric acid. The latter anion resulted also from the reaction of CS 2 and CsF with hexafluoropropene (HFP), whereas CS 2 , TMAF and HFP reacted to compounds derived from HFP dimerization. N,N -bis(2,2,2-trifluoroethyl)dithiocarbamic acid anion was obtained from bis(trifluoroethyl)amine reacted with CS 2 and TMAF.

ON THE FORMATION OF SURFACE ACTIVE BY-PRODUCTS DURING THE ELECTROCHEMICAL FLUORINATION OF TERTIARY AMINES

Abstract The electrochemical fluorination (ECF) of 2-phenyl-3,4-dimethylmorpholine led to the solubilization of the perfluoro products and HF foaming, which may be traced back to the formation of partially fluorinated, HF-soluble compounds which exhibit surface activity in HF. Some of the perfluoro products contain an asymmetric carbon atom attached directly to a cyclohexyl ring. This asymmetric centre leads to the non-equivalence of the fluorines bound to carbon atoms 2 and 6, respectively, of the cyclohexyl ring allowing them to be distinguished in the 19 F NMR spectra.

Asymmetric lamellar phospholipid aggregates bearing fluorocarbons

Abstract Phospholipid-encapsulated fluorocarbons form vesicle-like aggregates. Because of the lipophilic nature of fluo-rocarbons in the core, the number of surrounding lipid layers is consequently uneven. The lamellar structures of droplet coating have been confirmed by physical methods such as NMR spectroscopy, optical and cryo-electron microscopy, zeta potential, etc. The observed line broadening of signals in the 1H NMR spectra has been shown to be a result of hindered segmental motions in PFC-saturated lamellar structures. The existence of a negative surface charge as supported by the zeta potential contributes to an increase in the dispersion stability. Whereas light microscopy confirmed the isotropic nature of the dispersion, cryo-electron micrographs allowed the film thickness of the lamellae to be measured. The conditions under which such particles are prepared, especially the nature of the phospholipids used, are described. In addition, some new applications based on these aggregates are discussed.

Aspects of chemical and physical properties of perfluorochemicals and their emulsions

Abstract Perfluorochemicals (PFCs) dissolve ca. 40–50 vol % of oxygen and ca. 100–150 vol % of carbon dioxide. According to experiments and calculations, the physical solubility of oxygen cannot exceed 60 vol %. Emulsions of perfluorochemicals are used as oxygen carriers instead of blood. The surfactant most frequently used is Pluronic F-68, often with adjunction of yolk phospholipids, as in the case of Fluosol DA. These emulsions are difficult to formulate, it requires a high amount of energy, ultrasonic vibrations or pressure homogenization for instance, and a certain concentration of free surfactant. Even then stability is not assured, and the emulsions must be stored frozen. PFCs containing heteroatoms, especially in cyclic molecules form more stable emulsions. Therefore tailor-made PFCs are of interest. The possibilities for synthesis of these compounds are limited. By application of more effective surfactants emulsions can be prepared with contents of PFCs up to 50 vol %. These emulsions enable a better O 2 -delivery and have lower viscosities and smaller particle sizes.

Electrochemical fluorination as a route to perfluorocarbons useful for blood substitution

Abstract Perfluorocarbons (PFCs) useful for blood substitution have to meet the following requirements: very low toxicity, high oxygen solubility, good emulsifying properties, low vapour pressure, and high excretion rate. Therefore, a screening programme for new PFCs has to cover a great variety of candidates, very promising are those containing nitrogen. Among the methods for preparing selected PFCs, the electrochemical fluorination (ECF) plays the most important role. Very often ECF results in PFCs having the same carbon skeleton as the starting materials, especially in case of heteroatom containing substances. Charakteristically, there is a formation of splitting and rearrangement products as well, sometimes they become the only fluorination products. Examples are given for the ECF of heteroatom containing substrates together with an attempt to interpret the experimental data.