- Enthalpies of combustion of 2-iodosobenzoic acid and 4-nitrosophenol: The dissociation enthalpy of the I-O bond
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The standard (po = 0.1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, for crystalline 2-iodosobenzoic acid, (OI)C6H4COOH, and 4-nitrosophenol, (ON)C6H4OH, were measured by rotating-bomb calorimetry and static-bomb calorimetry, respectively. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds. ΔfHom(cr)/(kJ · mol-1) 2-iodosobenzoic acid 2-(OI)C6H4COOH -336.9 ± 2.5 4-nitrosophenol 4-(ON)C6H4OH -70.2 ± 2.1 An indirect method was used for assessing the dissociation enthalpy of the (I-O) bond in the iodoso derivative, Dom(I-O)/(kJ · mol-1) = (264.5 ± 8.1), which is the first value reported for an iodine-oxygen bond in an organic molecule.
- Ribeiro Da Silva, Maria D. M. C.,Matos, M. Agostinha R.,Ferrao, Maria Luisa C. C. H.,Amaral, Luisa M. P. F.,Miranda, Margarida S.,Acree Jr.,Pilcher
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- Decorating of ultra small and recyclable nanoscale zero-valent iron on NH2-SiO2 for enhanced high-performance removal of water pollutants
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The synthesis of nanoscale zero-valent iron (NZVI) with dimensions ranging from 20 to 100 nm has received tremendous attention in the control of environmental pollutants. However, due to strong magnetic attraction and van der Waals forces of NZVI, creating well-dispersed and stable NZVI particles with subnanometre size while avoiding their aggregation and retaining surface activity is a challenge. Here, for the first time, a novel Fe0@NH2-SiO2 nanocomposite was prepared by making SiO2 amino-functionalization in a simple process of hydrolysis polymerization, grafting Fe3+ on NH2-SiO2 nanospheres, and reduction by sodium borohydrid. It was found that the surface of NH2-SiO2 nanospheres (around 200 nm) was uniformly decorated by plentiful of well-defined Fe0 nanoparticles with a diameter of 0 nanoparticles showed a remarkable reduction activity in the application for the removal of water pollutants, and could be recycled easily with the aid of NaBH4.
- Shi, Dongyang,Zhu, Guifen,Zhang, Xia,Cheng, Meng,Wu, Tian,Zhang, Kaige,Fan, Jing
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- Green fabrication of 3-dimensional flower-shaped zinc glycerolate and ZnO microstructures for p-nitrophenol sensing
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The solvent or reaction medium always plays a lead role in synthesis chemistry. Glycerol has been studied as a green solvent for different organic transformations and is also expected to give interesting control in material synthesis. In this study, we use aqueous glycerol to synthesize zinc glycerolate and the corresponding ZnO micro-flower structures with an intention to encourage the utilization of glycerol as a green reaction medium in material synthesis. A zinc ammonium complex is used as a source of zinc, which converts to zinc glycerolate in the presence of glycerol. Glycerol plays a dual role as a reactant to form zinc glycerolate and as a solvent to control the morphology. The unreacted glycerol is recovered after the reaction and reused further. The flower-structured zinc glycerolate and ZnO are then used for the first time to modify a glassy carbon electrode to make a binder-free non-enzymatic amperometric chemical sensor for p-nitrophenol that is a brutal environmental pollutant. The modified electrode is found to be an excellent alternative for the purpose with respect to sensitivity, selectivity and stability.
- Sinhamahapatra, Apurba,Bhattacharjya, Dhrubajyoti,Yu, Jong-Sung
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- Investigation of photoelectrocatalytic activity of Cu2O nanoparticles for p-nitrophenol using rotating ring-disk electrode and application for electrocatalytic determination
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A cuprous oxide (Cu2O) nanoparticles modified Pt rotating ring-disk electrode (RRDE) was successfully fabricated, and the electrocatalytic determination of p-nitrophenol (PNP) using this electrode was developed. Cu2O nanoparticles were obtained by reducing the copper-citrate complex with hydrazine hydrate (N2H4·H 2O) in a template-free process. The hydrodynamic differential pulse voltammetry (HDPV) technique was applied for in situ monitor the photoelectrochemical behavior of PNP under visible light using nano-Cu 2O modified Pt RRDE as working electrode. PNP undergoes photoelectrocatalytic degradation on nano-Cu2O modified disk to give electroactive p-hydroxylamino phenol species which is compulsive transported and can only be detected at ring electrode at around 0.05 V with oxidation signal. The effects of illumination time, applied bias potential, rotation rates and pH of the reaction medium have been discussed. Under optimized conditions for electrocatalytic determination, the anodic current is linear with PNP concentration in the range of 1.0 × 10-5 to 1.0 × 10 -3 M, with a detection limit of 1.0 × 10-7 M and good precision (RSD = 2.8%, n = 10). The detection limit could be improved to 1.0 × 10-8 M by given illumination time. The proposed nano-Cu2O modified RRDE can be potentially applied for electrochemical detection of p-nitrophenol. And it also indicated that modified RRDE technique is a promising way for photoelecrocatalytic degradation and mechanism analysis of organic pollutants.
- Gu, Yong-E,Zhang, Yuzhen,Zhang, Fengyuan,Wei, Jinping,Wang, Chunming,Du, Yongling,Ye, Weichun
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- Nitrosation kinetics of phenolic components of foods and beverages
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The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5-5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO+/NO2H2+ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol > phenol ? p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH# against ΔS# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO+/NO2H2+.
- Paz Ferna?ndez-Liencres,Calle, Emilio,Gonza?lez-Mancebo, Samuel,Casado?, Julio,Quintero, Bartolome?
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- Nitrosation products from S-nitrosothiols via preliminary nitric oxide formation
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High yields of N-nitroso-N-methylaniline were obtained from S-nitrosothiols (RSNO) and N-methylaniline in water at pH 7.4. Reactions were completely inhibited by the presence of EDTA and also when oxygen was removed from the solutions. Lower yields of 4-nitrosophenol were obtained from phenol under similar conditions and there was strong evidence of the rapid formation of a nitroso product (absorbance maximum at 390 nm) from uric acid which decomposed more slowly under the reaction conditions and could not be isolated. The results are consistent with prior nitric oxide formation, by the well-known Cu2+-catalysed (in which the active reagent is Cu+) decomposition of the S-nitrosothiol, subsequent oxidation of NO yielding NO2, which reacts further with NO to give N2O3, which then effects conventional electrophilic nitrosation in direct competition with its hydrolysis to nitrite. With phenol as the reactant, higher yields of 4-nitrosophenol were only possible when there was a very large excess of phenol over RSNO, probably due to the more effective relative competition of the hydrolysis reaction, given the lower reactivity in nitrosation of phenol compared with N-methylaniline. Nitrosation of uric acid is unknown, but we were able to observe the fairly rapid build-up of the same absorbance at 390 nm, from uric acid and nitrous acid only at around pH 4, which disappeared more slowly. The results suggest that uric acid behaves as do amides generally in that a nitroso compound is formed, which decomposes by an acid-catalysed route.
- Noble, Darren R.,Williams, D. Lyn H.
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- Nitrosation of phenolic compounds: Inhibition and enhancement
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The nitrosation of phenol, m-, o-, and p-cresol, 2,3-, 3,5-, and 2,6- dimethylphenol, 3,5-di-tert-butylphenol, 2,4,6-trimethylphenol, o- chlorophenol, and o-bromophenol was studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the products at 345 nm. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of an attack on the nitrosatable substrate by NO+/NO2H2+, followed by a slow proton transfer. The finding of an isokinetic relationship supports the idea that the same mechanisms operates throughout the series. The observed sequence of nitrosatable substrate reactivities is explained by (i) the preferred para-orientation of the hydroxyl group for the electrophilic attack of nitrosating agents, (ii) steric hindrance of alkyl substituents, which reduces or prevents attack by nitrosating agents, and (iii) the hyperconjugative effect of the methyl substituent, which causes electronic charge to flow into the aromatic nucleus, as well as the opposite electronic withdrawing effect induced by halogen substituents. The results show that potential nitrosation of widespread environmental species such as chlorophenols is negligible, but more attention should be paid to polyphenols with strongly nucleophilic carbon atoms.
- Gonzalez-Mancebo, Samuel,Garcia-Santos, M. Pilar,Hernandez-Benito, Jesus,Calle, Emilio,Casado, Julio
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- N-Oxidation of arylamines to nitrosobenzenes using chloroperoxidase purified from Musa paradisiaca stem juice
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N-Oxidation of arylamines to their corresponding nitrosobenzenes using a new chloroperoxidase purified from Musa paradisiaca stem juice has been examined. The enzymatic characteristics of the stem chloroperoxidase using 4-chloroaniline as substrate were determined. The Km values for 4-chloroaniline and H2O2 were 770 μM and 154 μM respectively, while the pH and temperature optima were 4.4 and 30°C respectively. The substrate specificities of the enzyme for the arylamines 3,4-dichloroamine, p-aminobenzoic acid, p-toluidine, p-anisidine, m-anisidine, p-aminophenol, o-aminophenol and m-aminophenol have been characterized. The feasibility of using concentrated M. paradisiaca stem juice for the specific conversion of 4-chloroaniline to 4-chloronitrosobenzene has been demonstrated. This enzyme can be used for the N-oxidation of other arylamines.
- Yadav, Pratibha,Sharma, Jitendra K.,K. Singh, Vinod,Yadav, Kapil D. S.
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- Tungstate-supported silica-coated magnetite nanoparticles: a novel magnetically recoverable nanocatalyst for green synthesis of nitroso arenes
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Tungstate ion was heterogenized on the silica-coated magnetite nanoparticles and applied for the selective oxidation of anilines to nitroso arenes—with hydrogen peroxide/urea as oxidant in dimethyl carbonate as solvent—in moderate–good yields (40–96%). The catalyst was characterized using different techniques including Fourier-transform infrared spectroscopy, X-ray powder diffraction, vibrating sample magnetometry, scanning electron microscopy, energy dispersive X-ray and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The catalyst was easily recovered using an external magnet and reused for six times.
- Jadidi Nejad, Masoume,Yazdani, Elahe,Kazemi Miraki, Maryam,Heydari, Akbar
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p. 1575 - 1583
(2019/09/09)
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- Synthesis of Di(hetero)arylamines from Nitrosoarenes and Boronic Acids: A General, Mild, and Transition-Metal-Free Coupling
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The synthesis of di(hetero)arylamines by a transition-metal-free cross-coupling between nitrosoarenes and boronic acids is reported. The procedure is experimentally simple, fast, mild, and scalable and has a wide functional group tolerance, including carbonyls, nitro, halogens, free OH and NH groups. It also permits the synthesis of sterically hindered compounds.
- Roscales, Silvia,Csák?, Aurelio G.
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supporting information
p. 1667 - 1671
(2018/03/23)
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- Nitric Oxide Is Reduced to HNO by Proton-Coupled Nucleophilic Attack by Ascorbate, Tyrosine, and Other Alcohols. A New Route to HNO in Biological Media?
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The role of NO in biology is well established. However, an increasing body of evidence suggests that azanone (HNO), could also be involved in biological processes, some of which are attributed to NO. In this context, one of the most important and yet unanswered questions is whether and how HNO is produced in vivo. A possible route concerns the chemical or enzymatic reduction of NO. In the present work, we have taken advantage of a selective HNO sensing method, to show that NO is reduced to HNO by biologically relevant alcohols with moderate reducing capacity, such as ascorbate or tyrosine. The proposed mechanism involves a nucleophilic attack to NO by the alcohol, coupled to a proton transfer (PCNA: proton-coupled nucleophilic attack) and a subsequent decomposition of the so-produced radical to yield HNO and an alkoxyl radical. (Graph Presented).
- Suarez, Sebastián A.,Neuman, Nicolás I.,Mu?oz, Martina,álvarez, Lucía,Bikiel, Damián E.,Brondino, Carlos D.,Ivanovi?-Burmazovi?, Ivana,Miljkovic, Jan Lj.,Filipovic, Milos R.,Martí, Marcelo A.,Doctorovich, Fabio
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supporting information
p. 4720 - 4727
(2015/04/27)
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- Reactions of p-substituted phenols with nitrous acid in aqueous solution
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The reaction of phenols with nitrite (nitrous acid HONO, or its conjugated base, NO2-) is of importance in stomach fluids (low pH) and in atmospheric hydrometeors (mild acid and basic pH). The initial reaction associated with the oxidation/nitration of 4-substitued phenols promoted by HONO/NO2 depends on the pH of the solution. At low pH, the initial step involves the reaction between HONO and phenol, whereas at basic conditions this involves an electron transfer from the phenoxy anion to nitrogen dioxide (NO2) producing the nitrite anion. The rate of both processes is determined by the donor capacity of the substituent at the 4-position of the phenol, and the data obtained at pH 2.3 follow a linear Hammett-type correlation with a slope equal to -1.23. The partition of the gaseous intermediates (NO and NO2) makes the rate of HONO-mediated oxidation dependent on their gas-liquid distribution. At low pH, the main process is phenol oxidation, even in oxygen-free conditions, and the presence of any 4-substituted phenol decreases the rate of HONO auto-oxidation.
- Rubio, Maria A.,Lissi, Eduardo,Olivera, Nicol,Reyes, Jael L.,Lopez-Alarcon, Camilo
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p. 143 - 150
(2014/02/14)
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- Synthesis and characterization of azoxy based mesogenic diols
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Azoxy based rigid mesogenic diols have been synthesized using two steps. Phenol/cresol is used as starting material. Synthesized diols are characterized by IR, 1H and 13C NMR, and mass spectroscopic methods. Thermal properties have been determined by thermo gravimetric analysis method and crystallinity patterns have been obtained by wide angle X-ray diffractogram. Substituted phenol (methyl) is used to study the effect of substitution on physical and thermal properties of rigid azoxy mesogenic diol. The detailed characterization of azoxy based rigid diols is reported in this communication, which is highly useful for fundamental and applied research, particularly in liquid crystals and liquid crystalline polymers. The experimental results reveal that phenol based rigid mesogenic diols have high thermal stability and degree of crystallinity than methyl substituted rigid mesogenic diols.
- Mulani, Khudbudin B.,Ganjave, Nitin V.,Chavan, Nayaku N.
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p. 359 - 362
(2014/05/06)
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- NO2/H3BO3 as an effective nitrosonium source for electrophilic aromatic nitrosation under MW-promoted solvent-free conditions
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[Bmim]NO2/H3BO3 was used as a nitrosonium source for the efficient synthesis of nitrosoarenes. The reaction was accomplished under MW irradiation at 60 W in a solventless system. Side processes such as oxidation or dealkylation were not observed during the nitrosation of alkyl phenyl ethers in the presence of this new reagent. The satisfactory results were obtained with very short reaction time, simplicity in the experimental procedure and good to excellent yields.
- Valizadeh, Hassan,Gholipour, Hamid
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experimental part
p. 963 - 966
(2012/04/23)
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- New nitrite ionic liquid (IL-ONO) and nanoparticles of organosilane-based nitrite ionic liquid immobilized on silica as nitrosonium sources for electrophilic aromatic nitrosation
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An improved method for the synthesis of nitrosoarenes has been developed using a new nitrite ionic liquid (IL-ONO) and immobilized nitrite ionic liquid. These ionic liquids play as nitrosonium sources for electrophilic aromatic nitrosation of active aromatics at 0-5 °C. Their action was accomplished in water and the satisfactory results were obtained under the mild conditions in short reaction time.
- Valizadeh, Hassan,Amiri, Mohammad,Shomali, Ashkan
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experimental part
p. 1103 - 1108
(2012/03/10)
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- Selective N-oxidation of aromatic amines to nitroso derivatives using a molybdenum acetylide oxo-peroxo complex as catalyst
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The molybdenum acetylide oxo-peroxo complex obtained in situ by the treatment of the corresponding molybdenum acetylide carbonyl complex, CpMo(CO)3(C{triple bond, long}CPh); Cp = η5-C5H5 with H2O2, has been used as an efficient catalyst for selective N-oxidation of primary amines to nitroso derivatives. Excellent amine conversion (up to 100%) and very high selectivity for nitroso compounds (99%) have been obtained using 30% hydrogen peroxide as an oxidant. The oxo peroxo Mo(VI) complex has also been found to be very active for the oxidation of various substituted primary aromatic amines with electron donating as well as electron withdrawing substituents on the aromatic ring.
- Biradar, Ankush V.,Kotbagi, Trupti V.,Dongare, Mohan K.,Umbarkar, Shubhangi B.
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p. 3616 - 3619
(2008/09/19)
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- The mechanism by which 4-hydroxy-2,2,6,6-tetramethylpiperidene-1-oxyl (tempol) diverts peroxynitrite decomposition from nitrating to nitrosating species
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Tempol is a stable nitroxide radical that has been shown to protect laboratory animals from the injury associated with conditions of oxidative and nitrosoactive stress. Tempol's protective mechanisms against reactive oxygen species have been extensively studied, but its interactions with reactive nitrogen species remain little explored. Recently, it has been shown that tempol is a potent inhibitor of peroxynitrite-mediated phenol nitration while it increases phenol nitrosation by a complex mechanism [Carrol et al. (2000) Chem. Res. Toxicol. 13, 294]. To obtain further mechanistic insights, we reexamined the interaction of peroxynitrite with tempol in the absence and presence of carbon dioxide. Stopped-flow kinetic studies confirmed that tempol does not react directly with peroxynitrite but levels off the amount of oxygen (monitored with an oxygen electrode) and nitrite (monitored by chemiluminescence) produced from peroxynitrite in the presence and absence of carbon dioxide to about 30% and 70% of the initial oxidant concentration at pH 5.4, 6.4, and 7.4. Tempol inhibited phenol nitration while increasing the amounts of 4-nitrosophenol, that attained yields close to 30% of the peroxynitrite in the presence of carbon dioxide at pH 7.4. Fast-flow EPR experiments showed detectable changes in the instantaneous tempol concentration (maximum of 15%) only in the presence of carbon dioxide. Under these conditions, the instantaneous concentration of the carbonate radical anion was reduced by tempol in a concentration-dependent manner. The results indicate that tempol is oxidized by peroxynitrite-derived radicals (·OH and CO3·-, in the absence and presence of carbon dioxide, respectively) to the oxoammonium cation which, in turn, is reduced back to tempol while oxidizing peroxynitrite to oxygen and nitric oxide. The latter reacts rapidly with peroxynitrite-derived nitrogen dioxide to produce the nitrosating species, dinitrogen trioxide. Overall, the results support a role for peroxynitrite and its derived radicals in the tissue pathology associated with inflammatory conditions.
- Bonini, Marcelo G.,Mason, Ronald P.,Augusto, Ohara
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p. 506 - 511
(2007/10/03)
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- Nitrosation of phenolic compounds: Effects of alkyl substituents and solvent
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Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water/acetonitrile were studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO+/NO2H2+ followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron donating substituents, and a good Hammett correlation was observed with ρ=-6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH≈3, decreasing strongly for higher pH values. The study in water/acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant.
- Gonzalez-Mancebo, Samuel,Lacadena, Javier,Garcia-Alonso, Yolanda,Hernandez-Benito, Jesus,Calle, Emilio,Casado, Julio
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p. 157 - 166
(2007/10/03)
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- N-Arylhydroxamic acids as novel oxidoreductase substrates
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N-Arylhydroxamic acids (AHAs) are promising novel N-OH mediators for oxidoreductase catalysis. They are electrochemically active compounds with a redox potential of 0.31-0.41 V vs. SCE. Representative oxidoreductases, e.g. fungal peroxidase from Coprinus
- Kulys, Juozas,Deussen, Heinz-Josef,Krikstopaitis, Kastis,Lolck, Rikke,Schneider, Palle,Ziemys, Arturas
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p. 3475 - 3484
(2007/10/03)
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- An exceptionally stable Ti superoxide radical ion: A novel heterogeneous catalyst for the direct conversion of aromatic primary amines to nitro compounds
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A matrix-bound superoxide radical anion, generated by treating Ti(OR)4 (R =iPr, nBu) with H2O2, is a selective heterogeneous catalyst for the oxidation of anilines to the corresponding nitroarenes with 50 % aqueous H2O2 [Eq. (1)]. Yields of 82-98 % are obtained, even with anilines bearing electron-withdrawing substituents (R = NO2, COOH).
- Dewkar, Gajanan K.,Nikalje, Milind D.,Ali, Iliyas Sayyed,Paraskar, Abhimanyu S.,Jagtap,Sudalai
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p. 405 - 408
(2007/10/03)
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- Phenol photonitration upon UV irradiation of nitrite in aqueous solution I: Effects of oxygen and 2-propanol
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Nitrophenols are formed in aqueous solution upon UV irradiation of phenol and nitrite. The formation of nitrophenols is enhanced by dissolved oxygen and inhibited by the addition of 2-propanol. The mechanism of phenol photonitration involves both NO2 (or N2O4), reacting with phenol, and 4-nitrosophenol, which is oxidised to 4-nitrophenol. A reaction scheme is proposed based on experimental results.
- Vione, Davide,Maurino, Valter,Minero, Claudio,Pelizzetti, Ezio
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p. 893 - 902
(2007/10/03)
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- Phenol photonitration upon UV irradiation of nitrite in aqueous solution II: Effects of pH and TiO2
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Phenol photonitration and photonitrosation were studied both in homogeneous and in heterogeneous phase in the presence of TiO2 particles. The effect of pH as well as of the semiconductor particles on the kinetics and products of the reaction was observed. Formation of nitrophenols is enhanced at acidic pH, due to thermal processes initiated by nitrous acid, as well as in the presence of TiO2, due to the photocatalytic oxidation of nitrite.
- Vione, Davide,Maurino, Valter,Minero, Claudio,Pelizzetti, Ezio
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p. 903 - 910
(2007/10/03)
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- 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) inhibits peroxynitrite-mediated phenol nitration
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Peroxynitrite (PN), a very reactive oxidant formed by the combination of superoxide and nitric oxide, appears to play a role in producing tissue damage in a number of inflammatory conditions. Pharmacological scavenging and decomposition of PN within these areas has therapeutic value in several tissue injury models. Recently, we have been interested in nitroxide free radical-containing compounds as possible scavengers of PN decomposition products. Nitroxides can undergo redox reactions to the corresponding hydroxylamine anion or oxo-ammonium cation in biological systems as shown by its ability to react with superoxide, leading to the formation of hydrogen peroxide and molecular oxygen. We found that 4-hydroxy-2,2,6,6- tetramethylpiperidine-1-oxyl (Tempol) inhibits PN-mediated nitration of phenolic compounds in the presence of a large molar excess of PN, suggesting a catalytic-like mechanism. In these experiments, Tempol inhibited PN- mediated nitration over the pH range of 6.5-8.5. This inhibition was specific for nitration and had no effect on hydroxylation. After the inhibition of PN- mediated nitration, Tempol was recovered from the reaction mixtures unmodified. In addition, Tempol was effective in protecting PC-12 cells from death induced by SIN-1, a PN-generating compound. The exact mechanism of Tempol's interaction with PN is not clear; however, we propose that an intermediate in this reaction may be a nitrogen dioxide radical - Tempol complex. This complex could react with water to form either nitrite or nitrate, or with a phenol radical to produce nitrophenol or nitrosophenol products and regenerate the nitroxide.
- Carroll, Richard T.,Galatsis, Paul,Borosky, Susan,Kopec, Karla K.,Kumar, Vikram,Althaus, John S.,Hall, Edward D.
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p. 294 - 300
(2007/10/03)
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- Nitrosation of anisole, stability constants of complexes of the nitrosonium ion with aromatic nitroso compounds, and NMR studies of restricted rotation in the complexes
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Anisole can be nitrosated in good yield under the acidic and anaerobic conditions previously reported for methylbenzenes. The product, 4-nitrosoanisole, is slowly converted into 4-nitrosophenol in acetic-sulfuric acid mixtures. The decrease in the rate constant for this reaction with increasing concentration of nitrosonium ion leads to an estimate of the stability constant of the complex between 4-nitrosoanisole and nitrosonium ion. Stability constants for the similar complexes formed by 4-nitrosotoluene and 1,3-dimethyl-4-nitrosobenzene with nitrosonium ion in trifluoroacetic acid have been determined by UV spectroscopy. Restricted rotation about the bond between nitrogen and aromatic carbon is evident from the 1H NMR spectra of the complexes; activation parameters for the rotation are reported and compared with similar data in the literature for restricted rotation in uncomplexed aromatic nitroso compounds.
- Atherton, John H.,Moodie, Roy B.,Noble, Darren R.
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p. 229 - 234
(2007/10/03)
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- A study of the reaction of different phenol substrates with nitric oxide and peroxynitrite
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The reactivity of different phenol substrates with nitric oxide and peroxynitrite was investigated. In general, nitration is the major reaction with peroxynitrite, while reactions with aqueous solutions of nitric oxide led to mixtures of nitro and nitroso derivatives depending upon the phenol. Nitrosation occurs on phenol substrates bearing a free para- position with respect to the OH group with the exception of 1-naphthol, which afforded a 1:1 mixture of the 2- and the 4-nitroso derivatives. Chromans 7 and 8 showed the highest reactivity with peroxynitrite, which suggests that they can act as efficient scavengers of this toxic intermediate. In both cases the corresponding 5-nitro derivative was the only reaction product detected. Finally, the fact that chroman 8 reacts with nitric oxide to afford the p- quinone derivative 22a in 90% yield suggests that this antioxidant could also be of potential use as specific nitric oxide tracer in biological tissues.
- Yenes, Susana,Messeguer, Angel
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p. 14111 - 14122
(2007/10/03)
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- 4-acylaminopiperidin-N-oxyle
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4-Acylaminopiperidine N-oxides Ia where A1 is hydrogen or an organic radical and B1 is a radical IIa STR1 where R1 -R4 are each C1 -C4 -alkyl and R1 and R2, on the one hand, and R3 and R4, on the other hand, may furthermore be bonded to form a 5-membered or 6-membered ring, R5 is H or C1 14 C4 -alkyl and R6 is H or C1 -C18 -alkyl, are used for stabilizing organic materials against the harmful effect of free radicals, particularly in the distillation of monomers which undergo free radical polymerization, especially styrene.
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- Additional pathways of S-conjugate formation during interaction of 4- nitrosophenetole with glutathione
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The rapid reactions of nitrosoarenes with cellular SH groups have proved to be main metabolic conversions during detoxication. Interactions of the phenacetin metabolite 4-nitrosophenetole with glutathione have been investigated in detail during the last years, revealing a complex pattern of products depending on the stoichiometry of the reactants and reaction conditions. Eight metabolites have been identified hitherto, and the present work extends this medley by six additional products. Three metastable sulfenamides, 4-ethoxy-2,N-bis(glutathion-S-yl)-aniline, N4-(glutathion-S- yl)-4-amino-4'-ethoxydiphenylamine, and N-(glutathion-S-yl)-4-aminophenol, as well as the N-sulfenylquinonimine N-(glutathion-S-yl)-l,4-benzoquinonimine were characterized by chemical reactivity, chromatographic behavior, UV/vis absorption, 1H NMR, and FAB-MS data. The structure of the sulfenamide 2,N4- bis(glutathion-S-yl)-4-amino-4'-ethoxydiphenylamine could not be proved unequivocally, but is strongly suggested due to the chemical reactivity, chromatographic behavior, and UV/vis absorption of the compound. Finally, traces of 4-aminophenol were detected. A reaction scheme is presented explaining the formation of all identified metabolites via a central sulfenamide cation. Molecular orbital calculations for this sulfenamide cation have been performed, corroborating the proposed reaction mechanisms on the basis of Klopman's generalized perturbation theory.
- Gallemann, Dieter,Anke Greif, Peter Eyer,Wagner, Hans-Ulrich,Sonnenbichler, Johann,Sonnenbichler, Isolde,Schaefer, Wolfram,Buhrow, Ingrid
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p. 1411 - 1422
(2007/10/03)
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- Reactivity of phenolic nucleophiles towards nitroso compounds. Part 2. Reaction with alkyl nitrites (O-nitroso compounds)
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Second-order rate constants, k, have been measured for the reaction of substituted phenolate ions with alkyl nitrites in aqueous solution at 25 deg C. The final products of this reaction were identified as aromatic C-nitroso compounds and/or NO2-. Nitrosation of the phenolate ion yields ca. 90 percent of the p-nitroso product. However, methylation of the activated position of the ring (as in 4-methylphenol) does not result in the decrease in the overall reaction rate that would be expected. The reactivity of all the phenolate ions studied correlates well with their basicity, with the Hammett ?- constant and with their reactivity in other reactions in which they are known to act as O-nucleophiles. All these facts suggest that the reaction of aryloxide ions with alkyl nitrites always occurs through the oxygen atom to yield an unstable O-nitroso compound. This intermediate is likely to undergo an internal rearrangement of the NO group to give the corresponding C-nitroso product, competing with homolysis of the O-NO bond to yield nitric oxide. Oxidation of NO in the presence of O2 gives N2O3, which could act as a nitrosating agent towards ArO-. Hydrolysis of N2O3 in basic media accounts for the presence of the nitrite ion as one of the products.
- Leis, J. Ramon,Rios, Ana,Rodriguez-Sanchez, Luiza
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p. 2729 - 2734
(2007/10/03)
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- Photocatalytic interconversion of nitrogen-containing benzene derivatives
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The role of the electrons and holes at the surface of semiconductor oxides (TiO2 and WO3) in heterogeneous photocatalysis has been investigated in aqueous media for the reactions involving the series: nitrobenzene, nitrosobenzene, phenylhydroxylamine, aniline, and the related compound, 4-nitrosophenol. Qualitative and quantitative evaluation of most intermediates and their time evolution suggest that the reductive pathways are important and even predominant under a variety of experimental conditions. This aspect is not only true at the beginning of the process or for the readily reducible structures, but also during the entire degradation process. Each compound of the series is converted to all the others, even though in widely different amounts. In the early part of the photocatalytic process, with nitrosobenzene and with phenylhydroxylamine, even in the presence of oxygen, the nitrogen substituent undergoes simultaneous oxidation and reduction at comparable rates, so that very little change in the mean oxidation state of the system is observed. This suggests that photogenerated electrons have a controlling role, particularly for some compounds in the early steps of the photocatalytic transformation. For 4-nitrosophenol and p-benzoquinone, in the early steps of degradation the reductive pathways represent the main route, even in the presence of oxygen. As a consequence, for some compounds the presence of an excess of oxygen in the reacting atmosphere decreases the degradation rate, instead of promoting it, as is commonly observed in photocatalysis. It is also remarkable that, for some compounds examined, the redox reactions at the nitrogen-containing substituent have a comparable or even more important role than the hydroxylation of the aromatic ring, which was the predominant degradation pathway for most of the other aromatic compounds.
- Piccinini, Paola,Minero, Claudio,Vincenti, Marco,Pelizzetti, Ezio
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p. 1993 - 2000
(2007/10/03)
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- Nitroso Compounds by Reaction of Organomercurials with Nitrosyl Chloride
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By the reaction of RHgX (X = Cl, Br, OAc) with NOCl, mercury is eliminated as ClHgX and, if R is aromatic, nitroso compounds are obtained, i.e., nitrosobenzene, 1-nitrosonaphthalene, 4-nitroso-N,N-dimethylaniline, 2-nitrosophenol, 4-nitrosophenol and methyl 3-nitrososalicylate. If R is aliphatic or alicyclic, with RHgX to NOCl 1:3, gem-chloronitroso compounds are obtained that have not been described previously, i.e., 2-chloro-2-nitrosocyclohexanol, 1-acetoxy-2-chloro-2-nitrosocyclohexane, 1-chloro-2-methoxy-1-nitrosocyclopentane, methyl 2-chloro-2-nitroso-3-methoxypropionate, 1-chloro-1-nitroso-ethane and 2-chloro-2-nitrosoethanol. All products have been characterized by chemical and IR spectral analysis.
- Grdenic, Drago,Vrdoljak, Visnja,Korpar-Colig, Branka
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p. 1361 - 1366
(2007/10/03)
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- Protonation and Acid Catalysed Hydrolysis of Nitrosoaryl Ethers
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Studies of the equilibrium protonation and kinetics of acid catalysed hydrolysis of 4-nitrosoanisole, 4-nitrosophenyl phenyl ether and related compounds in dilute aqueous acid and in concentrated aqueous trifluoroacetic acid are reported.Hydrolysis is remarkably facile and occurs by nucleophilic attack of water at the ring carbon bearing the alkoxy or aryloxy substituent of the protonated nitroso aromatic.Direct and indirect pKa determinations for nitroso protonation are reported.
- Moodie, Roy B.,O'Sullivan, Brian
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p. 205 - 208
(2007/10/02)
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- Nitrosation by Alkyl Nitrites. Part 7. Comparsion with Thionitrites: Reactions with Phenols
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Both isopentyl nitrite (IPN) and S-nitroso-N-acetylpenicillamine (SNAP) react with phenol in the pH range 2 - 9 to give overwhelmingly 4-nitrosophenol.For IPN the reaction is first order in both IPN and phenol and the measured rate constant is much reduced by the addition of isopentyl alcohol, suggesting that reaction occurs by prior hydrolysis of IPN to nitrous acid.When allowance is made for the nitrous acid ionisation we find no acid catalysis in the pH range 3.62 - 5.25 but acid catalysis at higher acidities.The corrected rate constant also increases with pH at pH values greater than 6.There is no bromide ion catalysis at pH 4 but a substantial kinetic primary hydrogen isotope effect (using phenol) of 4.0 at pH 2.55 which decreases towards 1 as the pH is inreased.All of these results are consistent with rapid and reversible hydrolysis of IPN, and phenol nitrosation results from the nitrous acid produced.All of the experimental features parallel those found in the nitrous acid nitrosation of phenol.The kinetic pattern for the reaction of SNAP with phenol is quite different, showing autocatalytic features.We have obtained an EPR spectrum from the photolysis of SNAP, characteristic of RS., and for the phenoxy radical derived from the reaction mixture of SNAP with 2,6-di-tert-butyl-4-methylphenol at pH 7.We propose a radical mechanism for the reaction of SNAP with phenol involving hydrogen-atom abstraction by the RS. radical and subsequent reaction of the phenoxy radical with nitric oxide formed by homolysis of SNAP.
- Oh, Shirlene M. N. Y. F,Williams, Lyn H.
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p. 685 - 688
(2007/10/02)
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- Nitrosation and Nitrous Acid-catalysed Nitration of Anisole and 2,6-Dimethylanisole
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Rate-acidity profiles have been obtained for the nitrosation of anisole, 2,6-dimethylanisole (DMA), and 2,6-dimethylphenol (DMP) in aqueous sulphuric acid.The phenol is more reactive than the corresponding anisole, and DMA has a more shallow profile than anisole.A deuterium kinetic isotope effect (KH/kD) of 4.0 for 2H>anisole indicates that the product of nitrosation of anisole in 46.5percent sulphuric acid (p-nitrosophenol) is formed by slow proton loss from the Wheland intermediate.Intense colours were associated with the nitrosation of these compounds when nitrous acid was in excess.The kinetics of nitrous acid-catalysed nitration of anisole were studied in 43.0 and 47.0percent sulphuric acid; the product is p-nitrophenol.Nitrosation followed by oxidation by NV was the major pathway at these acidities.The other pathway has a kinetic form given by kC=k3III>V>, consistent with a process where oxidation by NV is rate-limiting.Product studies show that p-nitrophenol is formed at lower acidities and o- and p-nitroanisole at higher acidities.A mechanism is suggested involving a radical cation species, which would predominate at higher acidities and account for the kC pathway at lower acidities.The nitrous acid-catalysed nitration of DMA gives 2,6-dimethyl-4-nitroanisole in higher yield as the acidity increases.
- Dix, Leslie R.,Moodie, Roy B.
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p. 1097 - 1102
(2007/10/02)
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- The Nitrous Acid-catalysed Nitration of Phenol
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The reaction of phenol with nitrous acid (10E-4M III> V> III>V>/(xIII> + yV>).The x and y are constants for a given concentration of sulphuric acid.The dependence of x and y upon acidity, and comparison of the reactivity of phenol with that of hexadeuteriophenol and anisole, leads to a proposed mechanism for catalysed nitration.In this there is pre-equilibrium formation, from phenol and NIII, of an intermediate with the formula PhONO.This gives rise to a phenoxyl radical and nitric oxide, a step which is rate limiting when the rate is fully enhanced by V>.Nitric oxide is reversibly oxidised by NV to give NO2 and NIII.Reaction is completed by combination of the phenoxyl radical and NO2, in a step which is rate limiting when the rate is fully enhanced by III>.
- Al-Obaidi, Usama,Moodie, Roy B.
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p. 467 - 472
(2007/10/02)
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- Measurement of Acid-Base Equilibrium Constants in Acetonitrile/18-Crown-6 Solutions
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Absorbance data were collected at three wavelength for different mixtures of acetonitrile solutions of acetic acid and substituted phenolates in order to define ionic equilibria.Formation of hydrogen bonded adducts between acid and phenolate in concentration-dependent stoichiometry renders the data, even from very dilute solutions, too complex for an exact algebraic analysis.A quite accurate assessment of the acid-base equilibrium constants is possible, by using only the calculated concentrations of free acids and bases at each ratio of acid/base.Plotting such apparent equilibrium constants vs. the acid/base ratio permits an extrapolation to zero acid concentration in which limit the true value of the acid-base equilibrium constant can be obtained.A similar technique can lead to an estimation of formation constants for conjugate adducts in acetonitrile.
- Kovach, Ildiko M.
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p. 2184 - 2186
(2007/10/02)
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- Voltammetry of Acetamidophen and Its Metabolites
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As background support for a study of acetaminophen metabolism by modern electroanalytical and liquid chromatographic techniques, the voltammetric characteristics are reported for acetaminophen and representatives of its known classes of metabolites.Excellent agreement is found between cyclic voltammograms of millimolar solutions and hydrodynamic voltammograms derived from nanogram quantities studied by chromatographically assisted hydrodynamic voltammetry.This electrochemical information is expected to find application in the qualitative and quantitative determination of acetaminophen metabolites in samples of physiological origin, ultimately revealing new details about the mechanism of acetaminophen toxicity.This work provides a model which can be employed for the study of numerous toxic aromatic amines and phenols.
- Miner, David J.,Rice, John R.,Riggin, Ralph M.,Kissinger, Peter T.
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p. 2258 - 2263
(2007/10/02)
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- ISOMERIC COMPOSITION OF THE PRODUCTS FROM NITROSATION AND NITRATION OF PHENOL
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Under the conditions for the nitrosation of phenol by nitrous acid o-nitrosophenol is converted into the more stable para isomer.On the basis of the established reversibility of the nitrosation reaction and also of the results from investigation into the kinetics of the oxidation of o- and p-nitrosophenols by nitric acid a refined scheme of a "special" mechanism was proposed for the nitration of phenol by dilute nitric acid.By this means it is possible to explain the observed difference in the composition of the products from nitrosation and nitration of phenol and also the effect of nitrous acid on the direction of the latter.The formation of p-nitrosophenol as an intermediate product in the nitration of phenol was demonstrated by a kinetic method.
- Bazanova, G. V.,Stotskii, A. A.
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p. 2070 - 2075
(2007/10/02)
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- Mechanism of Decomposition of N-Hydroxyacetaminophen, a Postulated Toxic Metabolite of Acetaminophen
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The decomposition of N-hydroxyacetaminophen (N-acetyl-N-hydroxy-p-aminophenol, 2) a postulated toxic metabolite of acetaminophen (N-acetyl-p-aminophenol, 1) in aqueous solution is quantitatively accounted for by the appearance of equimolar amounts of p-nitrosophenol and acetaminophen.The rate of decomposition depends on initial concentration and varies with pH.Antioxidants decrease the rate of decomposition and change the products.In the presence of cysteine, N-acetyl-3-(S-cysteine)-p-aminophenol, an in vivo metabolite of acetaminophen, is a product of decomposition.
- Gemborys, Mark W.,Mudge, Gilbert H.
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p. 304 - 308
(2007/10/02)
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- Catalysis of Aromatic Nitration by the Lower Oxides of Nitrogen
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In the absence of nitrous acid traps, the nitration of phenol in 56.2percent sulphuric acid displays autocatalytic behaviour; on the other hand, the isomer ratio of the products is inconsistent with the commonly accepted prior nitrosation scheme, and some other route for the promotion of nitration must be operative.
- Ross, David S.,Hum, Georgina P.,Blucher, William G.
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p. 532 - 533
(2007/10/02)
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- RATIO OF NITROSATION AND OXIDATION RATES IN THE NITRATION OF PHENOL
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A mathematical analysis of the nitration of phenol by nitric acid in sulfuric acid solutions was undertaken on the basis of kinetic measurements on the nitrosation of phenol and the oxidation of nitrosophenol for the case of the para isomer.It was establi
- Bazanova, G. V.,Stotskii, A. A.
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p. 2075 - 2079
(2007/10/02)
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- Process for carrying out nitrosation reactions and diazotation reactions
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Process for carrying out nitrosation reactions and diazotization reactions by reacting the concerning compound with a nitrite in the presence of an acid wherein ammonium-nitrite is used as the nitrite.
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