- Synthesis of N-arylhydroxylamines by Pd-catalyzed coupling
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Pd-catalyzed coupling of aryl halides with TeocNHOTBS, followed by treatment of the products with TBAF, provides effective access to a wide range of N-arylhydroxylamines by a route that produces stable doubly-protected intermediates and allows the protective groups to be removed under mild conditions that do not cause extensive degradation of the final product.
- Beaudoin, Daniel,Wuest, James D.
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experimental part
p. 2221 - 2223
(2011/05/05)
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- Solvent hydrogen bonding and structural influences on the CrVI oxidation of anilines in aqueous acetic acid medium
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The oxidation of meta- and para-substituted anilines by CrVI oxidant, imidazolium fluorochromate (IFC), in aqueous acetic acid mixtures of varying compositions in the presence of p-toluenesulfonic acid (PTS) is first order in IFC and PTS. Michaelis-Menten type kinetics is observed with all of the anilines. The IFC oxidation of 15 meta- and para-substituted anilines at 299-322 K complies with the isokinetic relationship but not to any of the linear free energy relationships. The isokinetic temperature lies within the experimental range. The rate data failed to correlate with macroscopic solvent parameters such as relative permittivity, εr, and ionizing power, Y, correlation of rate data with Kamlet-Taft solvatochromic parameters (hydrogen bond donor acidity, α, hydrogen bond acceptor basicity, β, and dipolarity/polarizability, π*) is linear which suggests that the specific solute-solvent interactions play a dominating role in governing the reactivity.
- Bhuvaneshwari,Elango
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experimental part
p. 242 - 249
(2010/04/26)
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- Effect of solvent on the rate of oxidation of substituted anilines with nicotinium dichromate in aqueous-acetic acid media
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Mechanistic studies on the oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate in water-acetic acid medium of varying mole fractions have been performed. The reaction can be characterized by the experimental rate equation, -d[oxidizing agent]/dt = Kk [substrate] [HCrO 4-]/(1 + K [substrate]) The addition of p-toluenesulfonic acid enhances the reaction. The oxidation substituted anilines at 299-322 K complies with the isokinetic relationship but not to any of the linear free energy relationships, the isokinetic temperature lies within the experimental range. Correlation of rate data with Kamlet-Taft solvatochromic parameters (α, β, π*) suggests that the specific solute-solvent interactions play a major role in governing the reactivity.
- Bhuvaneshwari,Elango
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p. 999 - 1005
(2007/10/03)
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- Effect of substituents on the rate of oxidation of anilines with peroxomonosulfate monoanion (HOOSO3-) in aqueous acetonitrile: A mechanistic study
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Mechanistic studies on the oxidation of 18 meta-, para-, and ortho-substituted anilines (Ans) by HOOSO3- in aqueous acetonitrile medium have been performed. The reaction can be characterized by the experimental rate equation, -d[HSO5-]/dt = k[An][HSO5-] The addition of p-toluenesulfonic acid (TsOH) retards the reaction. The increase in the reactivity of anilines as the medium is made more aqueous is interpreted. The reaction is enhanced by electron-donating groups on the amine in the series consistent with the rate-limiting nucleophilic attack of the amine on the persulfate oxygen. The proposed mechanism involves the conversion of phenylhydroxylamine to nitrosobenzene in a fast step. The ESR study reveals the absence of free radicals in the reaction. Various attempts have been made to analyze the experimental rate constants in terms of LFER plots. Improved correlations are obtained with σ- values and the σ- form of the Yukawa-Tsuno equation.
- Meenakshisundaram, Subbiah,Selvaraju,Made Gowda,Rangappa, Kanchugarakoppal S.
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p. 649 - 657
(2007/10/03)
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- A novel strategy for the preparation of arylhydroxylamines: Chemoselective reduction of aromatic nitro compounds using bakers' yeast
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Using bakers' yeast as a biocatalyst, the chemoselective reduction of aromatic nitro compounds bearing electron-withdrawing groups gave the corresponding hydroxylamines with good to excellent conversion under mild conditions.
- Li, Feng,Cui, Jingnan,Qian, Xuhong,Zhang, Rong
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p. 2338 - 2339
(2007/10/03)
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- Mechanism and reactivity in perborate oxidation of anilines in acetic acid
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Perborate but not percarbonate in acetic acid generates peracetic acid on standing and the peracetic acid oxidation of anilines is fast. The oxidation with a fresh solution of perborate in acetic acid is smooth and second order but the specific oxidation rate increases with increasing [perborate]0 or [boric acid]. Perborate on dissolution affords hydrogen peroxide and a borate; the latter assists the former in the oxidation. The oxidation rates of anilines under identical conditions do not conform to any of the linear free energy relationships but the reaction rates of molecular anilines do. Perborate oxidation proceeds via two reaction paths but the overall oxidation rates of molecular anilines conform to structure reactivity relationships; the transition states do not differ significantly. Analysis of the oxidation rates of perborate and percarbonate reveals that while perborate oxidation is faster than percarbonate it is at least as selective as the latter.
- Karunakaran, Chockalingam,Kamalam, Ramasamy
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p. 2011 - 2018
(2007/10/03)
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- Kinetics and Mechanism of Oxidation of para-Substituted Anilines by Peroxomonosulphate
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Kinetics of oxidation of several para-substituted anilines by peroxomonosulphate (PMS) in aqueous acetic acid medium have been investigated. The reaction follows a total second order, first order each in [PMS] and [substrate]. The reaction rate is retarted by both electron-releasing and withdrawing groups. Absence of free radical formation is confirmed. Activation energy and thermodynamic parameters have been computed. A probable mechanism has been proposed.
- Abdul Jameel,Maruthamuthu
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p. 368 - 370
(2007/10/03)
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- Comparison of the reactivities of [Fe4S4(SPh)4]2- and [Fe2S2(SPh)4]2-
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The reactivities of the model complexes, [Fe4S4(SPh)4]2- (1) and [Fe2S2(SPh)4]2- (2), of nonheme iron-sulfur proteins were compared. Complex 1 catalyzed the oxidation of benzenethiol to diphenyl disulfide with the reduction of dioxygen to H2O. Complex 2 did not catalyze it, but the reaction proceeded after an induction period during which complex 2 was converted to complex 1. In addition, complex 1 catalyzed the reduction of 1,4-dinitrobenzene to N-(4-nitrophenyl)hydroxylamine (21%) and 4-nitroaniline (16%) with the oxidation of benzenethiol to diphenyl disulfide, but complex 2 induced mainly the displacement of nitro group to phenylthio group to give 1-nitro-4-(phenylthio)benzene (92%). It was revealed that the reactivities of complex 1 and complex 2 are quite different.
- Yanada,Nagano,Hirobe
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p. 208 - 210
(2007/10/02)
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- Competitive Base-Induced α-Elimination and Methanolysis of N-Aryl-O-pivaloylhydroxylamines
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The N-aryl-O-pivaloylhydroxylamines 1a-c are quite stable in MeOH under neutral conditions, but under mildly basic conditions (0.05 M Et2NH or Et3N) they undergo rapid decomposition (t1/2 = ca. 3-5 h at 25 deg C) by two competitive processes: apparent α-elimination to generate the nitrenes 2a-c and pivalic acid and basic ester methanolysis to generate the hydroxylamines 3a-c and methyl pivalate.The nitrenes decompose into the corresponding anilines 5 and azobenzenes 7, while the hydroxylamines undergo nitrene-mediated oxidation into the corresponding azoxybenzenes 6.The mechanism of this latter process was probed by addition of excess hydroxylamine, and a mechanism for the oxidation consistent with available data (Scheme II) is proposed.It was also found that the nitrosobenzenes 8 undergo nucleophilic attack by conjugate bases 4a-c of the title compounds to produce one of the two possible isomeric nonsymmetrical azoxybenzenes.
- Novak, Michael,Martin, Kristy A.,Heinrich, Julie L.,Peet, Kristine M.,Mohler, Linda K.
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p. 3023 - 3028
(2007/10/02)
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- Kinetics of the Reaction of p-Dinitrobenzene with Cyanide in Dimethylformamide
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The anion radical (pDNB-) is formed in the reaction of p-dinitrobenzene (pDNB) with cyanide in dry and oxygen-free dimethylformamide (DMF).The rate of the radical formation was studied spectrophotometrically in the concentration range 10-4 pDNB -3 mol dm-3 and 10-4 CN -2 mol dm-3.The rate was first order in p-dinitrobenzene.For cCN > 10-3 mol dm-3 the reaction was also first order in CN- with a second-order rate constant of (3.65 +/- 1.2) * 10-2 dm3 mol-1 s-1, an activation energy of (66 +/- 7) kJ mol-1, and an Arrhenius factor of 8.1 * 109 dm3 mol-1 s-1 (0-40 deg C).Radical formation is assumed to proceed via an intermediate Meisenheimer complex which reacts with a second cyanide ion to produce pDNB- and CN-.The formation of the Meisenheimer complex is assumed to be rate determining.
- Sauer, Alexandra,Wasgestian, Fritz,Barabasch, Beate
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p. 1317 - 1320
(2007/10/02)
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- Photochemistry in a Heterogenous System: Chlorophyll-Sensitized Reduction of p-Dinitrobenzene by Hydrazobenzene
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The photoreduction of p-dinitrobenzene, sensitized by aqueous suspensions of chlorophyll a with other amphiphiles adsorbed onto polyethylene-tetradecane particles, differs in some respects from the photoreduction in solution.The reaction proceeds in two stages.The products of the first stage, N-(p-nitrophenyl)hydroxylamine and azobenzene, are separated into the aqueous and hydrocarbon particles phases, respectively.The nature of the second stage of reaction is uncertain, but observations are best explained by a reduction of N-(p-nitrophenyl)hydroxylamine to 4,4'-dinitrohydrazobenzene.The quantum yield of photoreduction to the hydroxylamine does not seem to correlate at all with the quantum yield of fluorescence of the sensitizing particles.This and the relative magnitudes of the yields suggest that the principal photochemical reaction is reduction of dinitrobenzene not by the excited singlet state of chlorophyll or by the triplet state formed directly by intersystem crossing but by high-energy ion pair states or perhaps triplets formed from them by decay.Absorption spectrometry in the heterogeneous system is complicated by superposition of the so-called sieve effect on the path-lenth enhancement effect of the highly scattering system.The role of the interface between the particle and aqueous phases on the course of the reaction is discussed.
- Seeley, G. R.,Haggy, G. A.
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p. 440 - 447
(2007/10/02)
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- RUBREDOXIN MODEL COMPLEX (Et4N) AS A CATALYST IN THE REDUCTION OF AROMATIC NITRO COMPOUNDS TO HYDROXYLAMINES
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(Et4N), the analogue of oxidized rubredoxin active sites, can catalyze the reduction of aromatic nitro compounds to N-aryl hydroxylamines by o-xylene-α,α'-dithiol.
- Yanada, Kazuo,Nagano, Tetsuo,Hirobe, Masaaki
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p. 5113 - 5116
(2007/10/02)
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- Selenium-catalysed Reduction of Aromatic Nitro Compounds to N-Arylhydroxylamines
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Metallic selenium catalyses the reduction of aromatic nitro compounds to the corresponding N-arylhydrohylamines with sodium borohydride under mild conditions.
- Yanada, Kazuo,Yamaguchi, Hiromi,Meguri, Haruo,Uchida, Shuji
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p. 1655 - 1656
(2007/10/02)
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- Reduktion der Dinitrobenzole an Kohlenstoff-Faser-Elektroden in sauren und alkalischen waessrig-methanolischen Loesungen
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The electrochemical reduction of the isomeric dinitrobenzenes at carbon fibre electrodes is investigated in aquoues-methanolic solutions, for a large pH-range (pH = 1-13), by means of cyclic voltammetry and constant potential electrolysis. o- and p-Dinitrobenzene are reduced from acidic and neutral solutions first to nitrophenylhydroxylamine and then to phenylendiamine.In alkaline solutions the above substances are finally reduced to phenylendiamine having nitrophenylhydroxylamine and aminophenylhydroxylamine as intermediate products.In the case of p-dinitrobenzene a stable quinoid dianion is formed in strong alkaline solutions, which finally yields p-phenylendiamine at higher negative potentials.The formation of a similar o-quinoid dianion is impossible due to steric interactions. m-Dinitrobenzene is reduced, for the overall pH-range investigated, to m-phenylendihydroxylamine, passing intermediately by m-nitrophenylhydroxylamine.Key words: Dinitrobenzenes / Carbon fibre electrodes / Cyclic voltammetry / Constant potential electrolysis
- Jannakoudakis, P. D.,Theodoridou, E.
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