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EPR Study of Radical Intermediates of H-transfer from Oxygeneous, Carboneous and Nitrogeneous Donors
Marešová, Renata ; Mazúr, Milan (referee) ; Stopka, Pavel (referee) ; Omelka, Ladislav (advisor)
Within the PhD. thesis the problems of H-transfer from selected types of phenols, aromatic secondary amines and compounds with acidic CH bond were investigated. This process was initiated by the action of redox agents, mostly PbO2, in nonpolar solvents. The abstraction of hydrogen atom results in the formation of radical intermediates, which were detected by EPR spectroscopy. Because in most cases, highly unstable radicals were produced, it was neccessary to apply the technique of indirect detection, so called spin trapping. This method enables to interpret the character of generated radicals on the basis of EPR parameters of radical adducts, which are formed by their reaction with suitably chosen compounds, spin traps, which are added to the reaction system. As spin traps, the aromatic nitrosocompounds were preferentially used. Due to the fact that EPR spectra of radical adducts were in most cases very complex, their interpretation was possible only using the computer simulation. Based on this approach, new information about the character of addition of phenoxyl tradicals to aromatic nitrosocompounds, stability of alkyl substituents in methyl substituted phenols and character of C-radicals, generated from substituted coumarines and beta-diketones, was obtained. Simultaneously, the small ability of nitrogen radicals, primary products of the splitting of NH bond, to enter the reaction with spin traps was proved by aromatic secondary amines.
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Radical Reactions of the Decomposition of N-H, O-H and O-O Bonds Initiated by Homogeneous and Heterogeneous Redox Agents
Majzlík, Petr ; Mazúr, Milan (referee) ; Stopka, Pavel (referee) ; Omelka, Ladislav (advisor)
The Ph.D. thesis was focused on EPR study of redox reactions of selected types of phenols, secondary amines and diperoxy coumpounds. Within the study some redox agents were employed in nonpolar, in some special cases also in polar solvents. EPR spectra of generated radical products were interpreted using spectral simulation. Study of radical reactions under participation of phenols was preferentially concentrated on the behavior of para methyl substituted phenols, where the instability of this substituent in relation to the applied redox agents was evaluated. The tendency towards the abstraction of hydrogen from methyl group, representing the paralell mechanism to the hydrogen abstaction from phenolic OH group was proved. The generated benzyl radicals were undirectly detected in the form of adducts with aromatic nitroso compounds. These adducts undergo the consecutive transformations, leading to the formation of new types of phenoxy radicals. The study of the decomposition of NH bonds was performed with substituted N,N´-paraphenylenediamines, 1-anilino-1-phenylpentane-3-ones and amino substituted 1,3-dimethyluracils. By the oxidation with 3-chloroperbenzoic acid the corresponding nitroxyl radicals were prepared. In the case of 1-anilino-1-phenylpentane-3-ones the aminyl radicals were prepared by the oxidation with PbO2, which existence was evidenced by spin trapping method with nitrosobenzene. In the framework of the investigation of the decomposition of -O-O- bonds the oxygen centred radicals, generated from peroxidic compounds of Luperox type using selected redox agents were detected by spin trapping method. The analysis of EPR spectra documented that primary alkoxyl radicals undergo the consecutive fragmentation, which leads in the presence of oxygen to the formation of secondary alkoxyl radicals. The generation of oxygen centred radicals during the decomposition was indirectly proved in the presence of model phenolic compounds, where due to the abstraction of hydrogen from phenolic OH group the phenoxyl radicals are formed.
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EPR Study of Radical Reactions of Secondary Amines in Liquid Phase
Šafaříková, Lenka ; Lehocký,, Marián (referee) ; Mazúr, Milan (referee) ; Omelka, Ladislav (advisor)
In the framework of Ph.D. thesis the evaluation of radical reactions of four groups of secondary amines R1–NH–R2 in the presence of some selected types of agents was performed using EPR spectroscopy. First group was represented by peroxoagents (3-chloroperbenzoic acid, tBuO2 radicals), the second group involved compounds of PbIV+ (PbO2, Pb(OAc)4) functioning as hydrogen-abstracting agents. In the presence of peroxyagents the formation of corresponding aminoxyl radicals R1–NO–R2 was demonstrated. In the case of surplus of tBuO2 radicals these radicals enter the consecutive reactions which products are new types of secondary aminoxyls. By the interpretation of reaction mechanism the intermediary formation of nitrones was assumed. These function in later steps of the reaction as spin traps for tBuO2 radicals. By the study of radical mechanism of amines R1–NH–R2 initiated by PbIV+ agents was proved, that these compounds hydrogen atom not only from –NH– group under formation of aminyl radicals, but also from C–H bonds in substituents R1, R2 (the formation of C-radicals). Because both groups of the radicals formed are characterized by high reactivity, their identification was possible only using spin-trapping method. In the course of the investigation of radical reactions of secondary amines the big amount of experimental EPR spectra was obtained. These exhibited in many cases very high hyperfine structure. Due to this fact it was necessary to perform the detailed evaluation on the basis of spectral simulation. Except of some special cases using this approach the interpretation of majority of registered EPR spectra was interpreted and EPR parameters were summarized in tables.
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Radical products of the oxidation of selected phenols and amines
Holubcová, Petra ; Mazúr, Milan (referee) ; Omelka, Ladislav (advisor)
In the framework of diploma thesis, radical products of the oxidation of selected paramethyl phenols and secondary amines were investigated. In the case of para-methyl phenols using EPR spectroscopy the reaction mechanism was proved, where the abstraction of hydrogen from para-methyl group is involved. In this way benzyl radicals are formed, which can be identified by spin-trapping technique using nitroso compounds. The adducts formed undergo the consecutive rearrangement, which leads to the formation of the corresponding nitrones. In addition to phenols, the radical products of the oxidation of some secondary amines using peroxy radicals and peroxy acids were studied. In both cases new types of nitroxyle radicals were generated and the EPR parameters were determined by spectral simulation.
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Radical intermediates generated by the splitting of X-H bond in different types of H-donors
Šafaříková, Lenka ; Mazúr, Milan (referee) ; Omelka, Ladislav (advisor)
In the frame of submitted diploma thesis dealing with the radical products of the decomposition of different X-H bonds, primary attention was focused on the detection of radical intermediates from decomposed N-H bonds. This access was realized with secondary amines of N-alkylaniline group, as well as with other structures R1-NH-R2. The aim was to confirm the formation of unstable aminyl radicals R1-N•-R2, which is possible by using spin-trapping method. In the series of experiments, where the compounds of lead and cobalt, as well as stable radical DPPH were applied as initiators of the decomposition, the unambiguous evidence for aminyl radicals was found only in the case of N-alkylanilines. With other secondary amines the detection of aminyl radicals is an open problem, because their adducts with nitrosobenzene are in very low concentration. Besides the study of the decomposition of N-H bonds also the products of the decomposition of phenolic O-H bonds, as well as products of the decomposition of C-H bonds in alkylsubstituents in phenols was studied.
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Application of Quantitative Electron Paramagnetic Resonance (EPR) and Commercially Available EPR Standards for Electrochemical Study of the Subsituted Tetrathiafulvalene Oxidation.
Habániková, Shannelle Diana ; Tarábek, Ján (advisor) ; Mazúr, Milan (referee)
Tetrathiafulvalene derivatives are remarkable molecules, with various application, reported relatively recently. The radical cation of these compounds has very inter- esting optical, electronic, electrocatalytic superconducting and magnetic properties that have been intensively studied recently. Quantitative in-situ EPR voltammetric spectroelectrochemistry studies of 2-(2-hydroxyethylsulfanyl)-3-(benzylsulfanyl)-6,7- bis(octadecylsulphanyl)tetrathiafulvalene (TTF-Der3) have been carried out with the aim to confirm the oxidation sites, follow-up reactions (after the first electron transfer), and electrochemical behaviour. The diffusion process was confirmed by the depen- dence of current on the square root of the scan rate. It was claimed that the ratio of the number of generated radicals to transferred charge (electrons) for two representative TTF derivatives was determined to 5.5:500 for and 7:500 for TTF, indicating the follow- up reactions. Experiments were performed using the commercially available EPR standards, calibrated for this method (experimental setup). The latter was validated by quantitative EPR with standard 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl radical concentration (1·10−4 mol dm−3). For the ratios the confidence interval was reported for the first time for TTF-Der3 it was...
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EPR Study of Radical Reactions of Secondary Amines in Liquid Phase
Šafaříková, Lenka ; Lehocký,, Marián (referee) ; Mazúr, Milan (referee) ; Omelka, Ladislav (advisor)
In the framework of Ph.D. thesis the evaluation of radical reactions of four groups of secondary amines R1–NH–R2 in the presence of some selected types of agents was performed using EPR spectroscopy. First group was represented by peroxoagents (3-chloroperbenzoic acid, tBuO2 radicals), the second group involved compounds of PbIV+ (PbO2, Pb(OAc)4) functioning as hydrogen-abstracting agents. In the presence of peroxyagents the formation of corresponding aminoxyl radicals R1–NO–R2 was demonstrated. In the case of surplus of tBuO2 radicals these radicals enter the consecutive reactions which products are new types of secondary aminoxyls. By the interpretation of reaction mechanism the intermediary formation of nitrones was assumed. These function in later steps of the reaction as spin traps for tBuO2 radicals. By the study of radical mechanism of amines R1–NH–R2 initiated by PbIV+ agents was proved, that these compounds hydrogen atom not only from –NH– group under formation of aminyl radicals, but also from C–H bonds in substituents R1, R2 (the formation of C-radicals). Because both groups of the radicals formed are characterized by high reactivity, their identification was possible only using spin-trapping method. In the course of the investigation of radical reactions of secondary amines the big amount of experimental EPR spectra was obtained. These exhibited in many cases very high hyperfine structure. Due to this fact it was necessary to perform the detailed evaluation on the basis of spectral simulation. Except of some special cases using this approach the interpretation of majority of registered EPR spectra was interpreted and EPR parameters were summarized in tables.
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Radical Reactions of the Decomposition of N-H, O-H and O-O Bonds Initiated by Homogeneous and Heterogeneous Redox Agents
Majzlík, Petr ; Mazúr, Milan (referee) ; Stopka, Pavel (referee) ; Omelka, Ladislav (advisor)
The Ph.D. thesis was focused on EPR study of redox reactions of selected types of phenols, secondary amines and diperoxy coumpounds. Within the study some redox agents were employed in nonpolar, in some special cases also in polar solvents. EPR spectra of generated radical products were interpreted using spectral simulation. Study of radical reactions under participation of phenols was preferentially concentrated on the behavior of para methyl substituted phenols, where the instability of this substituent in relation to the applied redox agents was evaluated. The tendency towards the abstraction of hydrogen from methyl group, representing the paralell mechanism to the hydrogen abstaction from phenolic OH group was proved. The generated benzyl radicals were undirectly detected in the form of adducts with aromatic nitroso compounds. These adducts undergo the consecutive transformations, leading to the formation of new types of phenoxy radicals. The study of the decomposition of NH bonds was performed with substituted N,N´-paraphenylenediamines, 1-anilino-1-phenylpentane-3-ones and amino substituted 1,3-dimethyluracils. By the oxidation with 3-chloroperbenzoic acid the corresponding nitroxyl radicals were prepared. In the case of 1-anilino-1-phenylpentane-3-ones the aminyl radicals were prepared by the oxidation with PbO2, which existence was evidenced by spin trapping method with nitrosobenzene. In the framework of the investigation of the decomposition of -O-O- bonds the oxygen centred radicals, generated from peroxidic compounds of Luperox type using selected redox agents were detected by spin trapping method. The analysis of EPR spectra documented that primary alkoxyl radicals undergo the consecutive fragmentation, which leads in the presence of oxygen to the formation of secondary alkoxyl radicals. The generation of oxygen centred radicals during the decomposition was indirectly proved in the presence of model phenolic compounds, where due to the abstraction of hydrogen from phenolic OH group the phenoxyl radicals are formed.
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EPR Study of Radical Intermediates of H-transfer from Oxygeneous, Carboneous and Nitrogeneous Donors
Marešová, Renata ; Mazúr, Milan (referee) ; Stopka, Pavel (referee) ; Omelka, Ladislav (advisor)
Within the PhD. thesis the problems of H-transfer from selected types of phenols, aromatic secondary amines and compounds with acidic CH bond were investigated. This process was initiated by the action of redox agents, mostly PbO2, in nonpolar solvents. The abstraction of hydrogen atom results in the formation of radical intermediates, which were detected by EPR spectroscopy. Because in most cases, highly unstable radicals were produced, it was neccessary to apply the technique of indirect detection, so called spin trapping. This method enables to interpret the character of generated radicals on the basis of EPR parameters of radical adducts, which are formed by their reaction with suitably chosen compounds, spin traps, which are added to the reaction system. As spin traps, the aromatic nitrosocompounds were preferentially used. Due to the fact that EPR spectra of radical adducts were in most cases very complex, their interpretation was possible only using the computer simulation. Based on this approach, new information about the character of addition of phenoxyl tradicals to aromatic nitrosocompounds, stability of alkyl substituents in methyl substituted phenols and character of C-radicals, generated from substituted coumarines and beta-diketones, was obtained. Simultaneously, the small ability of nitrogen radicals, primary products of the splitting of NH bond, to enter the reaction with spin traps was proved by aromatic secondary amines.
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Radical intermediates generated by the splitting of X-H bond in different types of H-donors
Šafaříková, Lenka ; Mazúr, Milan (referee) ; Omelka, Ladislav (advisor)
In the frame of submitted diploma thesis dealing with the radical products of the decomposition of different X-H bonds, primary attention was focused on the detection of radical intermediates from decomposed N-H bonds. This access was realized with secondary amines of N-alkylaniline group, as well as with other structures R1-NH-R2. The aim was to confirm the formation of unstable aminyl radicals R1-N•-R2, which is possible by using spin-trapping method. In the series of experiments, where the compounds of lead and cobalt, as well as stable radical DPPH were applied as initiators of the decomposition, the unambiguous evidence for aminyl radicals was found only in the case of N-alkylanilines. With other secondary amines the detection of aminyl radicals is an open problem, because their adducts with nitrosobenzene are in very low concentration. Besides the study of the decomposition of N-H bonds also the products of the decomposition of phenolic O-H bonds, as well as products of the decomposition of C-H bonds in alkylsubstituents in phenols was studied.
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