Hasso Meinert

Über die eigenionisation der halogenfluoride

Zusammenfassung Es wird eine Vorstellung fur die Eigenionisation der Halogenfluoride am Beispiel des BrF 3 entwickelt. Daneben werden die Beweise fur eine Eigenionisation dieser Verbindungen kritisch diskutiert. Aus den eigenen Arbeiten mit BrF 5 glauben wir, das gemas de 18 F-Austauschreaktionen, der elektrochemischen, spektroskopischen und chemischen Untersuchungen BrF 5 nur unwesentlich dissoziiert vorliegt, wobei das Ionengleichgewicht fur chemische Reaktionen belanglos ist. Die Halogenfluoride reagieren mit Lewissauren und -basen als molekulare Verbindungen im Sinne von Donator-Akzeptor-Reaktionen.

Über synthesen von difluoraminopyrimidinen

Zusammenfassung Es wird uber Synthesen von Difluoraminopyrimidinen berichtet. Bei der Direktfluorierung der Aminoderivate worden die entsprechenden Difluoraminoverbindungen neben weiteren Fluorierungsprodukten erhalten. Im Falle der Alkylierung von Difluoramin durch protonierte Pyrimidine wird die Bildung der Difluoraminoverbindungen diskutiert.

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.

ESR-Measurements on radicals generated in perfluorocarbons

Abstract Perfluorocarbons (PFC) are well-known as compounds useful as blood substitutes. Because of immiscibility in water PFC can only be used as O/W- emulsions. Therefore emulsions stable over a long period of time are necessary. For this reason attempts to determine structure-property relationships and the chemical behaviour are required. An interesting class of compounds which should be included are highly fluorinated olefines like 1 and 2 . According to Riess [1] these compounds are supposed to belong to the second generation of blood substitutes. CF3(CF2)nCF2CHCHCF2(CF2)nCF3 n = 2 and 4 1 and 2 The existence of the double bond, perhaps comparible to a heteroatom, appears to favour emulsion stability. The lack of chemical inertness of the double bond, however, could effect toxicity in medical application. Therefore chemical reactions of 1 and 2 were investigated, which had been started by -radiation and UV-irradiation, respectively. Different mechanisms have to be taken into account for variable conditions e.g. temperature from 77 to 300 K, presence of oxygen. The following radicals were detected by ESR: primary radicals of 1 and 2 , different types of peroxyradicals and of aggregates. Under UV-excitation at 300 K the concentration of paramagnetic species observed by cw-ESR depends strongly on experimental conditions: wavelength of excitation, exposure time and the presence of an sensitizing agent. Consequences of the above-mentioned questions are discussed.

Determination of particle size distribution in perfluorocarbon emulsions

Abstract The application of oil/water-emulsion of perfluorocarbons (PFC) as oxygen-carrying media for medical purpose requires the consideration of several prerequisities. For instance, the emulsion must not contain particles with a diameter larger than 400 nm. Otherwise, the reticuloendothelial system is blocked quickly by larger particles showing toxic effects. Therefore, a method is desirable which makes possible a fast determination of particle size and size distribution. Measurements of PFC-emulsions have shown that the desired informations can be obtained from dynamic light scattering. The experimental autocorrelation function yields a mean particle diameter and some information about the polydispersity of the emulsion. Moreover, performing the inverse Laplace transformation of the autocorrelation function by the method of Provencher (1), the size distribution of the scattering particles in the emulsion can be evaluated. In this connection, a model for light scattering of PFC-particles with surfactants like Pluronic F-68 was developed, which is based on PFC-spheres enveloped by a surfactant layer. The thickness of this layer can be assumed to be in the range from 5 to 1O nm. The above-mentioned technique has been used for the characterization of several PFC-emulsions. The influence of temperature, time of storage and additives have been investigated. First conclusions of conditions which influence floculation and coalescence, respectively, are drawn. The results are compared with others known from literature.

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.

New surfactants for preparing perfluorocarbonemulsions

Abstract For the preparation of finedispersed stable emulsions the following prerequisites in regard to the emulsifier have to be noticed seriously from the viewpoint of surface chemistry: • Surface and interface tensions σ, γ. • Time dependence of γ as to judge diffusion rates. • Wetting and spreading on a low energy surface proved by contact angle ⊖. • Mechanical-rheological stability of adsorbed films on droplets examined by light absorption (optical density vs time) at 540 nm. In this respect the commonly used emulgator Pluronic F 68 has been investigated in comparison with the novel PFC-modified polyol emulgator prepared it ourselves [1]. Synthesis is done by reacting fluoroolefins and fluorinated carboxylic acid derivates, respectively with oligomer polyols according to

Incandescent lamps with a fluorine cycle and filaments of tungsten or carbon

Abstract Tungsten-bromine or iodine lamps are now approaching the maximum performance that can be expected from commercially available tungsten wire and within the accuracy of present filament making equipment. To date, the development of a defect-healing tungsten-fluorine cycle holds the greatest promise for the immediate future, and with the innovation of a fluorine and fluoride resistant coating to protect the lamp envelope, the protection of the cooler regions of the filament, the prevention of the disproportionation blackening of lower tungsten fluorides and the control of the quantity of free fluorine throughout the life of the lamp, the principal technological problems seems to be solved. Although alternative materials with a higher melting point than that of tungsten are available, as yet, none satisfies the additional essential criteria for a filament material, especially of low vapour pressure. This means that under the same operating conditions, the bulb wall of a tungsten filament lamp does not blacken nearly as quickly as that of a carbon-filament lamp. Nethertheless, the carbon-filament lamp does have its virtues. Much more information is now available about the various kinds of carbon. Also there is the question of possible shortage of materials; there is some risk of this with tungsten, but not with carbon. Therefore we used the chemical transport reactions between elementary carbon and carbon fluorine species to retransport the carbon evaporated from the filament. These processes are discussed and compared with the tungsten fluorine cycle in an incandescent lamp.