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EPR study of radical reactions initiated by the decomposition of selected types of peroxy compounds
Krkošková, Petra ; Kučerík, Jiří (referee) ; Omelka, Ladislav (advisor)
The products of the decomposition of selected types of peroxo compounds in the presence of redox agents (Pb and Co compounds) were investigated by EPR method. Besides some commercial peroxides the study was performed with peroxo compounds of Luperoxide group (Luperox 101, Luperox 256, Luperox 531). For the detection of the decomposition products the technique of spin-trapping using nitrosobenzene was applied. EPR spectra of radical adducts formed by the reaction of the reactive oxygenous radicals with nitrosobenzen having the character of stable nitroxyl radicals were analyzed. Their EPR parameters were obtained by simulation method. Besides the addition to nitrosobenzene the generated oxygen centered radicals were proved also on the basis of their reaction with model compounds (Santonox R; 2,6–ditercbutyl–4–methylphenol; diphenylamine).
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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 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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Spin-trapping of radical products of H-transfer from oxygeneous donors
Šafaříková, Lenka ; Polovka, Martin (referee) ; Omelka, Ladislav (advisor)
Within the bachelor thesis the evaluation of experimental material focused on EPR study of spin-trapping of phenoxyl radicals on aromatic nitrosocompounds was performed. It was found that phenoxyl radicals from unhindered phenols add to nitrosogroup in the ortho-position. As a result, the nitroxyl radicals are formed. According to the structure of nitrosocompounds this nitroxyl radicals have the character either of phenoxazinoxyl radicals in the case of nitrosobenzene or derivatives of diphenylnitroxyl radical in the case of nitrosoduren. In the work is also documented the specific behavior of some phenols containing methyl group as the para substituent.
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Spin-trapping of radical products of H-transfer from carboneous donors
Krkošková, Petra ; Polovka, Martin (referee) ; Omelka, Ladislav (advisor)
On example of special type of a coumarine derivatives and also compounds with character of esters and diesters, which have an –CHR- group between two carbonyl groups or between carbonyl and imino group, the possibility of detection of C-radicals resulting from the homolytic splitting of the C-H bond of a methylene group was studied. PbO2 was used as an appropriate compound, on which surface the coumarine derivatives and the other compounds are decomposed. C-radicals were investigated by means of technique of spin-trapping and by comparison of experimental and simulated EPR spectra.
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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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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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EPR study of radical reactions initiated by the decomposition of selected types of peroxy compounds
Krkošková, Petra ; Kučerík, Jiří (referee) ; Omelka, Ladislav (advisor)
The products of the decomposition of selected types of peroxo compounds in the presence of redox agents (Pb and Co compounds) were investigated by EPR method. Besides some commercial peroxides the study was performed with peroxo compounds of Luperoxide group (Luperox 101, Luperox 256, Luperox 531). For the detection of the decomposition products the technique of spin-trapping using nitrosobenzene was applied. EPR spectra of radical adducts formed by the reaction of the reactive oxygenous radicals with nitrosobenzen having the character of stable nitroxyl radicals were analyzed. Their EPR parameters were obtained by simulation method. Besides the addition to nitrosobenzene the generated oxygen centered radicals were proved also on the basis of their reaction with model compounds (Santonox R; 2,6–ditercbutyl–4–methylphenol; diphenylamine).
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