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Hrvoj Vancik - One of the best experts on this subject based on the ideXlab platform.
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mechanosynthesis of Nitrosobenzenes a proof of principle study in combining solvent free synthesis with solvent free separations
Green Chemistry, 2012Co-Authors: Igor Huskic, Ivan Halasz, Tomislav Friscic, Hrvoj VancikAbstract:Mechanochemical Oxone oxidation of selected para-substituted anilines was used as a rapid and solvent-free route to Nitrosobenzenes; besides avoiding bulk solvents and short reaction times, this method exploits high vapour pressures of Nitrosobenzenes for the solvent-free separation of the product by sublimation, demonstrating an entirely solvent-free route to chemical synthesis and product isolation.
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Dimerization of Nitrosobenzene Derivatives on an Au(111) Surface
The Journal of Physical Chemistry C, 2011Co-Authors: Ivana Biljan, Marko Kralj, Tea Mišić Radić, Vesna Svetličić, Hrvoj VancikAbstract:In this study, we have investigated the ability of C-Nitrosobenzenes to dimerize on an Au(111) surface and form ordered self-assembled bilayers (SABs). Use of scanning tunneling microscopy (STM) revealed that Nitrosobenzene derivatives are able to form both well-ordered monolayers (SAMs) and bilayers (SABs). High-resolution STM images showed that within SAM regions molecules are arranged into hexagonal structures. Moire-type superstructure with a periodicity of 1.5 nm was observed, indicating a 3√3 × 3√3 molecular arrangement. Molecularly resolved STM images showed that within bilayers molecules are also arranged into hexagonally ordered structures at intermolecular spacing of ∼0.4 nm. Furthermore, it was observed that the second layer is better ordered than the first one, probably because of the softer background. Use of atomic force microscopy (AFM), through measured height differences between monolayers and bilayers, further confirmed the formation of SABs. The results of the present study demonstrate ...
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Nitrosobenzene cross-dimerization: Structural selectivity in solution and in solid state
Journal of Molecular Structure, 2010Co-Authors: Ivana Biljan, Gorana Cvjetojevic, Vilko Smrecki, Predrag Novak, Gregor Mali, Janez Plavec, Darko Babic, Zlatko Mihalic, Hrvoj VancikAbstract:Possibility of Nitrosobenzenes to form dimeric molecular structures (azodioxides) is used as a model for intermolecular selectivity investigations in solution as well as in solid state. Cross-dimerization of different combinations of p- and m-substituted Nitrosobenzene pairs was studied by variable temperature 1H NMR, solid-state NMR (CP MAS), IR, and ab initio calculations. It is evident that p-nitroNitrosobenzene behaves nonselectively because it forms dimers with all the studied Nitrosobenzene partners. In contrast, p-methoxyNitrosobenzene in most cases does not form dimers. The evidence that ability to form dimers is different in solution than in the solid state can be explained by influence of molecular arrangements in the crystal lattice
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Nitrosobenzene dimerizations as a model system for studying solid-state reaction mechanisms.
The Journal of organic chemistry, 2004Co-Authors: Hrvoj Vancik, Vesna Simunic-meznaric, Ernest Meštrović, Ivan HalaszAbstract:Thermal dimerization of nitroso compounds in the solid state was investigated by using para-substituted Nitrosobenzenes as model compounds. A mechanism that includes the interplay of topochemical reaction trajectories and phase transfer was proposed on the basis of FT-IR spectroscopic kinetics, time-resolved powder diffraction, and low-temperature X-ray structure determination. From shapes of the kinetic curves analyzed on the basis of the Avrami model, it was found that phase transfer could be triggered by a dimerization reaction of para-substituted Nitrosobenzene to azodioxide, which, in turn, can be caused by different packing factors such as disorder in the starting nitroso monomer crystals. Since the represented model can be extended to a broad series of compounds, we propose it as a general method for investigations of solid-state reaction mechanisms.
Vladimir Ponec - One of the best experts on this subject based on the ideXlab platform.
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An FTIR Spectroscopic Study of the Selective Oxidation of Nitrosobenzene to Nitrobenzene by Metal Oxides
Journal of Catalysis, 1996Co-Authors: S. Meijers, Vladimir PonecAbstract:Catalytic conversion of nitro- into Nitrosobenzene by transition metal oxides is of considerable practical and theoretical interest. Therefore, the surface chemistry of Nitrosobenzene on various metal oxides has been studied using IR spectroscopy. The main products of surface reactions are nitrobenzene and azoxybenzene. Findings of this study are compared with the results of a mass spectroscopic study carried out with Nitrosobenzene on the same oxides. Molecularly adsorbed Nitrosobenzene is found to be coordinated to metal cations by σ-N as well as σ-O bonds. Also thecis-dimer of Nitrosobenzene is detected. As a reference, the spectra of adsorbed Nitrosobenzene were compared with the spectra of monomeric Nitrosobenzene dissolved in benzene and dimeric Nitrosobenzene dissolved in ethanol. Some IR absorptions not reported earlier are assigned to C–N stretching and ring vibrations of σ-O coordinated and dimeric Nitrosobenzene. The coordination modes of Nitrosobenzene observed with the different oxides, and the reverse relationship found between ν(N=O) and ν(C–N) are in agreement with the observations made with nitroso compounds coordinated as ligands in organometallic complexes. A link to the catalytic behavior of Nitrosobenzene on oxides is indicated.
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The Role of the Mars and Van Krevelen Mechanism in the Selective Oxidation of Nitrosobenzene and the Deoxygenation of Nitrobenzene on Oxidic Catalysts
Journal of Catalysis, 1995Co-Authors: E.j. Grootendorst, Y. Verbeek, Vladimir PonecAbstract:The role of lattice oxygen atoms in the oxidation of Nitrosobenzene to nitrobenzene has been established by using isotopically labeled oxides and, in other experiments, 18O2 as oxidant. It appeared that with the most active catalyst, α-Mn3O4, the Mars and van Krevelen mechanism (oxidation by lattive oxygen atoms) is the most important mechanism. On γ-Fe2O3 and γ-Al2O3, disproportionation of Nitrosobenzene prevails.
Stanislav Biskupič - One of the best experts on this subject based on the ideXlab platform.
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EPR study of photoinduced reduction of nitroso compounds in titanium dioxide suspensions
Journal of Photochemistry and Photobiology A-chemistry, 2003Co-Authors: Vlasta Brezová, Peter Tarábek, Dana Dvoranová, Andrej Staško, Stanislav BiskupičAbstract:Abstract The radical intermediates produced upon UV irradiation of deoxygenated alcoholic titanium dioxide suspensions of Nitrosobenzene, nitrobenzene, 2-nitrosotoluene, 2,3,5,6-tetramethylNitrosobenzene, 3,5-di-bromo-4-Nitrosobenzenesulfonate (sodium salt), 2,4,6-tri-t-butyl-nitroso-benzene, and 2-methyl-2-nitrosopropane were investigated using in situ EPR technique. Nitrosobenzene is efficiently photoreduced in TiO2 suspensions (toluene/alcohol, 1:1 (v/v)) forming exclusively one stable radical intermediate corresponding to C6H5N OH species. The formation of this radical species is consistent with the proposed photocatalytic reduction mechanism, occurring from the primary generated Nitrosobenzene mono-anion by the hydrogen abstraction from surroundings. The origin of hydrogen added to the nitroso group was demonstrated by the photocatalytic experiments using deuterated methanol, where the production of C6H5N OD was established. Additionally, an identical radical C6H5N OH was detected, when nitrobenzene was reduced under analogous experimental conditions. The photoinduced electron transfer from TiO2 to nitroso compounds is accompanied by alcohol oxidation via the photogenerated titanium dioxide valance band holes forming alkoxy and hydroxyalkyl radicals. Production of hydroxyalkyl radicals ( CH2OH, CH(OH)CH3, C(OH)(CH3)2) with redox potentials suitable for a direct electron transfer to nitroso compounds represents an alternative reaction pathway for their reduction. On the other hand, the investigated nitroso derivatives are efficient spin-trapping agents, therefore, formation of nitroxyl radical spin adducts was observed in the photocatalytic experiments. The EPR spectra monitored upon irradiation of substituted Nitrosobenzene derivatives in alcoholic TiO2 suspensions reveal the correlation between Nitrosobenzene derivative first step reduction potentials and yield of radical species produced.
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EPR study of photoinduced reduction of nitroso compounds in titanium dioxide suspensions
Journal of Photochemistry and Photobiology A-chemistry, 2003Co-Authors: Vlasta Brezová, Peter Tarábek, Dana Dvoranová, Andrej Staško, Stanislav BiskupičAbstract:Abstract The radical intermediates produced upon UV irradiation of deoxygenated alcoholic titanium dioxide suspensions of Nitrosobenzene, nitrobenzene, 2-nitrosotoluene, 2,3,5,6-tetramethylNitrosobenzene, 3,5-di-bromo-4-Nitrosobenzenesulfonate (sodium salt), 2,4,6-tri-t-butyl-nitroso-benzene, and 2-methyl-2-nitrosopropane were investigated using in situ EPR technique. Nitrosobenzene is efficiently photoreduced in TiO2 suspensions (toluene/alcohol, 1:1 (v/v)) forming exclusively one stable radical intermediate corresponding to C6H5N OH species. The formation of this radical species is consistent with the proposed photocatalytic reduction mechanism, occurring from the primary generated Nitrosobenzene mono-anion by the hydrogen abstraction from surroundings. The origin of hydrogen added to the nitroso group was demonstrated by the photocatalytic experiments using deuterated methanol, where the production of C6H5N OD was established. Additionally, an identical radical C6H5N OH was detected, when nitrobenzene was reduced under analogous experimental conditions. The photoinduced electron transfer from TiO2 to nitroso compounds is accompanied by alcohol oxidation via the photogenerated titanium dioxide valance band holes forming alkoxy and hydroxyalkyl radicals. Production of hydroxyalkyl radicals ( CH2OH, CH(OH)CH3, C(OH)(CH3)2) with redox potentials suitable for a direct electron transfer to nitroso compounds represents an alternative reaction pathway for their reduction. On the other hand, the investigated nitroso derivatives are efficient spin-trapping agents, therefore, formation of nitroxyl radical spin adducts was observed in the photocatalytic experiments. The EPR spectra monitored upon irradiation of substituted Nitrosobenzene derivatives in alcoholic TiO2 suspensions reveal the correlation between Nitrosobenzene derivative first step reduction potentials and yield of radical species produced.
G Pilcher - One of the best experts on this subject based on the ideXlab platform.
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enthalpies of combustion of 2 2 6 6 tetraethylazobenzenen n dioxide 2 4 6 tri 1 1 dimethylethyl Nitrosobenzene and 2 4 6 tri 1 1 dimethylethyl nitrobenzene
The Journal of Chemical Thermodynamics, 1995Co-Authors: William E Acree, Simon G Bott, Sheryl A Tucker, Maria Ribeiro D M C Da Silva, M A R Matos, G PilcherAbstract:The standard (p∘= 0.1 MPa) molar enthalpies of combustion at the temperatureT= 298.15 K were measured by static-bomb calorimetry for crystalline 2,2′6,6′-tetraethylazobenzeneN,N-dioxide, { 2,6-(C2H5)2C6H3N(O)·}2; 2,4,6-tri(1,1-dimethylethyl)Nitrosobenzene, 2,4,6-{CH3C(CH3)2}3C6H2NO; and 2,4,6-tri(1,1-dimethylethyl)nitrobenzene, 2,4,6-{ CH3C(CH3)2}3C6H2NO2. The standard molar enthalpies of sublimation atT= 298.15 K of the tri(1,1-dimethylethyl) compounds were measured by microcalorimetry. [Table] The standard molar enthalpy of decomposition of {2,6-(C2H5)2C6H3N(O)·}2to form 2,6-(C2H5)2C6H3NO(g) atT= 298.15 K was measured by microcalorimetry: ΔdecHom/kJ·mol−1) = (200.6 ± 5.6). Application of group-additivity schemes applied to Nitrosobenzene and nitrobenzene derivatives shows that 2,4,6-tri(1,1-dimethylethyl)Nitrosobenzene is unstrained whereas the corresponding nitrocompound shows considerable strain in accord with an X-ray structure analysis demonstrating that steric hindrance prevents dimerization of the nitrosoderivative.
Ivan Halasz - One of the best experts on this subject based on the ideXlab platform.
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mechanosynthesis of Nitrosobenzenes a proof of principle study in combining solvent free synthesis with solvent free separations
Green Chemistry, 2012Co-Authors: Igor Huskic, Ivan Halasz, Tomislav Friscic, Hrvoj VancikAbstract:Mechanochemical Oxone oxidation of selected para-substituted anilines was used as a rapid and solvent-free route to Nitrosobenzenes; besides avoiding bulk solvents and short reaction times, this method exploits high vapour pressures of Nitrosobenzenes for the solvent-free separation of the product by sublimation, demonstrating an entirely solvent-free route to chemical synthesis and product isolation.
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Nitrosobenzene dimerizations as a model system for studying solid-state reaction mechanisms.
The Journal of organic chemistry, 2004Co-Authors: Hrvoj Vancik, Vesna Simunic-meznaric, Ernest Meštrović, Ivan HalaszAbstract:Thermal dimerization of nitroso compounds in the solid state was investigated by using para-substituted Nitrosobenzenes as model compounds. A mechanism that includes the interplay of topochemical reaction trajectories and phase transfer was proposed on the basis of FT-IR spectroscopic kinetics, time-resolved powder diffraction, and low-temperature X-ray structure determination. From shapes of the kinetic curves analyzed on the basis of the Avrami model, it was found that phase transfer could be triggered by a dimerization reaction of para-substituted Nitrosobenzene to azodioxide, which, in turn, can be caused by different packing factors such as disorder in the starting nitroso monomer crystals. Since the represented model can be extended to a broad series of compounds, we propose it as a general method for investigations of solid-state reaction mechanisms.
