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FOX-7 - Study of Reduction Products of Spectroelectrochemical Methods
Šimková, Ludmila ; Dmitrieva, E. ; Klíma, Jiří ; Dunsch, L. ; Ludvík, Jiří
A new energetic material 2,2-dinitroethene-1,1-diamine (FOX-7) is recently broadly tested because of its high performance and very low sensitivity. On the other hand, its electrochemical and redox properties have not been studied yet. Our results show that FOX-7 is reduced in aprotic solvents only by two one-electron steps up to -2.9 V. The color changes during reduction of FOX-7 and reversibility of the redox process indicate the presence of radical intermediates. Therefore in situ UV-vis-NIR and ESR spectroelectrochemical investigations were performed. The products after exhaustive electrolyses were separated by HPLC and are identified by mass spectrometry. The possible formation of gaseous products was followed online EC-GC.
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Electrochemical and spectrometric study of FOX-7 in aprotic solvents
Šimková, Ludmila ; Ludvík, Jiří ; Klíma, Jiří
2,2-Dinitroethene-1,1-diamine (FOX-7) is a recently developed and broadly tested energetic material with high efficiency and low sensitivity. Generally, explosion is based on thermally initiated chain of intramolecular redox reactions. Recently it has been found that electrochemical reduction in aqueous solutions is also able to provoke the chain of follow-up processes leading to total decomposition of the parent substance yielding gaseous products analogously like during explosion. Similarly, results from reductive electrolysis of FOX-7 in aprotic solvents show analogous course of degradation. The first transferred electron activates the molecule and initiated the formation of colored radical intermediates that have been spectroscopically characterized
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Carbon nanotubes - material for carbon paste electrodes, possibilities of preparation and characterization
Mikysek, T. ; Stočes, M. ; Švancara, I. ; Ludvík, Jiří
In this article, some new approaches to characterize the carbon paste mixtures and the respective carbon nanotube paste electrodes (CNTPEs) are presented, discussed. Particular attention has been paid to the changes of the ohmic resistance, relative to the dependence on composition of the CNTPE, the materials used, the time. Four types of carbon nanotube pastes were examined, and for the interpretation of experimental data. Some problems connected with homogeneity and stability of carbon pastes, their storage, or eventual aging effects are also discussed.
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Strange Redox Behavior of 1,1-Diamino-2,2-dinitroethene
Šimková, Ludmila ; Ludvík, Jiří ; Klíma, Jiří
The expected product of polarographic reduction of 1,1-diamino-2,2-dinitroethene (FOX-7) in aqueous buffered solutions is ethan-1,2-diamine. But exhaustive electrolysis did not show this product. The main products are gases. Due to combination of electrochemistry and GC and with MS analysis were found following gaseous products: N-2, NO, N2O, H2O. However, no carbon containing gaseous product was found. A part of products remains probably in the water solution as inorganic ions. The degradation process accompanying the exhaustive electrolysis seems to be analogous to the reactions during explosion, but under very low concentration, cooled and slowed down by the solvent.
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Electrochemistry of halogenated benzenonitrils
Sokolová, Romana ; Pospíšil, Lubomír ; Hromadová, Magdaléna ; Ludvík, Jiří
Autoprotonation in reduction mechanism of 3,5-dihalogeno-4-hydroxy-benzonitriles was studied in dimethylsulfoxide by electrochemical methods. The overall one electron reduction process was found. Aryl radical formed by the cleavage of halogenide undergroes further electron transfer in EC type reaction. The anion is protonated by parent molecule resulting in total consumption of two electrons per two starting molecules. Addition of stronger proton donor increases the height of reduction wave up to two electrons per molecule. The addition of potassium hydroxide causes the decrease of the reduction wave. The reduction products were identified by GC/MS analysis in the absence and presence of strong proton donor.
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Some New Approaches to the Characterization of the Carbon Paste Electrodes
Mikysek, T. ; Švancara, I. ; Ludvík, Jiří ; Vytřas, K. ; Kalcher, K.
Uhlíkové pastové elektrody mají dvě hlavní výhody: jejich povrch lze snadno reprodukovatelně obnovovat a dále, je možné je modifikovat v objemu za účelem získání specifických senzorů. Příprava těchto elektrod však závisí jednak na použitých materiálech, tedy na uhlíkovém prášku i na olejovém médiu, jednak na jejich vzájemném poměru. To umožňuje velikou variabilitu vlastností, současně ale otázka charakterizace těchto elektrod je velmi významná. Bylo zjištěno, že graf závislosti odporu elektrody na jejím složení je ve tvaru dvou protínajících se přímek. K vysvětlení této závislosti byl navržen, testován a diskutován model vycházející z představy těsně uspořádaných koulí (známé z krystalografie). Další způsob charakterizace těchto elektrod je založen na interpretaci cyklických voltamogramů nějakého dobře reverzibilního systému. Obě tyto metody jsou kompatibilní, navíc umožňují vysvětlení dalších jevů spojených s morfologií a se stárnutím těchto elektrod.
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Intramolekulární elektronová interakce dvou typů dikarbonylových slouočenin a jejich derivátů – elektrochemická a kvantově chemická studie
Ludvík, Jiří ; Celik, H. ; Jirkovský, Jaromír ; Zuman, P.
In the frame of studies of molecules with two redox centers, two isomeric monooximes derived from aryl-alkyl 1,2-diketones were electrochemically investigated. Whereas 1-phenyl-2-oxo-1-oximinopropane is reduced in acidic media according to the mechanism typical for oximes, that means by fou electrons yielding aminoketone, which is further reduced bielectronically under splitting of ammonia, its isomer 1-phenyl-1-oxo-2-oximinopropane is reduced to the stable 1-hydroxy-2-aminoolefine (enol form) and this corresponds to the reduction mechanism of benzil. It is surprising that the unsymmetric molecule behaves like the symmetric one. Basing on the electrochemical data and their correlation with quantum chemical calculations it was possible to explain this phenomenon.
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Electrochemical investigation of intramolecular electronic interactions in substituted nitrobenzens
Liška, A. ; Ludvík, Jiří
This research represents the first part of the electrochemical study of nitrocalixarenes. The title compounds represent thus the "monomeric" fragments and their models. The electrochemical reduction of aromatic nitrocompounds in non-aqueous media proceeds generally in two steps: one-electron reversible formation of radical anion and three-electron reduction to the hydroxylamine. In this work, however, four other different mechanisms of electroreduction of aromatic nitrocompounds are presented and the influence od p-substituents on the reduction pattern are discussed.
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