Elektrochemische synthesen—XXI. Cyclovoltammetrische und epr-spektroskopische untersuchung des redoxverhaltens des [S4N5]−-ions

Whilst the anodic oxidation of (Bu₄N) [S₄N₅] in 0,15 M (Bu₄N) [BF₄]/CH₂Cl₂ yielded no detectable radical species, the cathodic reduction at ?40°C and at room temperature leads to epr spectra, which can be assigned to [S₄N₅]^2? and [SN₂]^? plus a species containing one N atom—possibly NS^.₂.     

Elektrochemische Umwelttechnik

Electrochemical processes in environmental protection. Electrochemical processes can contribute considerably to environmental protection by means of waste purification processes and production integrated waste minimization. In the field of waste purification, electrochemical gas purification, purification of metal containing waste waters, and the electrolytic decomposition of neutral salt solutions will be illustrated by examples. As examples of production-integrated environmental protection, this article considers fluidized bed electrolysis, membrane process for alkali chloride electrolysis, and electroreduction of dichloroacetic acid.     

Elektrochemische Energiespeicherung

Electrochemical storage of energy. Besides energy density, performance density, and lifetime, the overall efficiency represents a very important criterion for electro-chemical energy storage systems and influences the costs significantly. The system electrolyser – hydrogen storage – fuel cell exhibits an overall efficiency of about 1/3, half as much as an accumulator. On the other hand, it favours long term storage of energy. Organic liquids, especially methanol which can be synthesised by CO₂ hydrogenation, seem to be the most promising mode of storing hydrogen. No optimal system is available yet for the short- or mid-term storage of photovoltaic solar energy in buildings. Connection to the public mains will be the best approach. For special purposes like emergency power sources or load levelling systems the lead accumulator is still interesting. However, electrochemical storage systems exhibit the most promise for energy saving as mobile power sources such as improved accumulators or in the longer term as fuel cells, e. g. for electrically driven vehicles. Some relevant options are outlined.     

Elektrochemische Reduktion von Trichloracetaldehyd-Olefin-Additionsprodukten

Electrochemical Reduction of Trichloroacetaldehyde-Olefin-Addition-Products Trichloroacetaldehyde reacts with different olefins forming addition products. In most cases this reaction results in 1, 1, 1-trichloro-2-hydroxy compounds (2a–d) . But also a different route of reaction is possible. Thus 2, 3-dimethylbut-1-ene (1e) forms 4-trichloro-1, 1, 2-tetrahydroxy-furane (2e) and cyclohexene (1f) forms 3-trichloromethyl-2-oxabicyclo-2, 2, 2-octane (2f) . All addition products are suitable starting materials for electrochemical conversions. In acidic electrolytes, on lead cathodes the electrochemical reduction results in a simultaneous cleavage of a C Cl and a C O bond to form the CHCCl₂-group (3a-f) . In neutral electrolytes, on mercury cathodes, however, a reductive conversion of a CCl₃ – group to a CHCl₂-group takes place ( 4c , 4f ).     

Elektrochemische Carboxylierung substituierter Vinylketone

Electrochemical Carboxylation of Substituted Vinyl Ketones α-Chlor-β-acyl-vinylsulphides ( 1a–f ) and keten-S, N-acetales ( 3a,b ) are reduced in the presence of CO₂ at the cathode to yield the corresponding acids ( 4a–f resp. 5). Whereas the carboxylation of 1 proceeds via elimination-addition mechanism, the reduction of 3 is similar to the keten-S, S-acetales described earlier an EC (addition) EC (elimination) sequence.     

Elektrochemische Adamantylierung von Styrylpyridinen

Electrochemical Adamantylation of Styrylpyridines The reaction between electrochemically generated anion radicals of the 4-(4-styryl)-pyridines 1–6 and 1-bromoadamantane gives, in solvents of low proton availability as N, N dimethylformamide via an electron transfer in solution and formation of 1-adamantyl-radicals, monoadamantylated pyrid-4-yl-phenylethanes. The major product results from an anion radical/radicalcoupling in the 2(β)- next the 1(α)-position. A competing pathway of the electrohydroadamantylation is the hydrogeneration of the  CHCH double bond, whose importance increases with the water content of the solvent. Based on cyclic-voltammetric evidence and product distribution, the mechanism of the reductive coupling of 1–6 in the presence of 1-bromoadamantane in discussed in terms of indirect electrolysis.     

Elektrochemische Energieumwandlung in Brennstoffzellen

Electrochemical energy conversion in fuel cells. With the exception of high temperature fuel cells, fuel cells burn hydrogen fuel exclusively at low temperature giving energy conversion efficiencies of 40 to 60%. Alkaline cells, phosphoric acid cells, and membrane cells operate at low temperatures, whereas molten carbonate cells and zirconium dioxide membrane cells are designed as high temperature cells. The alcaline fuel cell has so far been used only for special purposes, such as space missions and miltary applications. The phosphoric acid cell is suitable for modular heating plant between 0.5 and 5 MW which are fueled with natural gas. It has demonstrated its technical reliability in a large-scale field test in the USA and an economical breakthrough is expected in the next few years. The two high temperature cells face a longer development phase, yet hold promise of better econmic performance thanks to their greater efficiency.     

Elektrochemische Darstellung von organischen Diseleniden

Electrochemical Preparation of Organic Diselenides By the method of electrosynthesis a number of organic diselenides can be prepared simply and without danger. The cathodic polarisation of a special selenium electrode in aprotic solutions gives rise to polyselenideanions, which react with electrophilic compounds to the corresponding diselenides of the general formula RSeSeR ( 2a–e ) with R = benzyl, 2-nitrophenyl, cyclohexyl, isopropyl, 4-cyanophenyl.     

Radiochemische untersuchung der austauschgeschwindigkeit von harzaustauschern

The determination of half life times for the exchange on resins using labelled strontium ions and two different methods shows the influence of cross-linking, grain size and porosity. The big pores of the macroporous resins effect the exchange in the inner parts of the grains to be approximately as fast as in the outer parts.     

Elektrochemische Adamantylierung von reduktiv dehalogenierbaren Chinolinen

Electrolytic Adamantylation by Reductive Coupling of Quinolinylhalides in the Presence of 1-Bromoadamantane Electrochemically generated anion radicals of a number of halogen-substituted quinolines 1 a–g dehalogenate in N,N-dimethylformamide to halogen anions and radicals, which may stabilize by hydrogen abstraction from the solvent. In the presence of 1-bromoadamantane the fragments of reductive dehalogenation may be used synthetically for indirect generation of 1-bromoadamantane-radicals, which react predominantly to cross-coupled 2- and 7-monoadamantylated dihydroquinoline- and quinoline-structures, independent of the original halogen position. If C-2 is blocked, adamantylation takes place in the carbocyclic ring. Product distribution and cyclic-voltammetric results are discussed in terms of mechanism.