- Nitroxyl radical plus hydroxylamine pseudo self-exchange reactions: Tunneling in hydrogen atom transfer
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Bimolecular rate constants have been measured for reactions that involve hydrogen atom transfer (HAT) from hydroxylamines to nitroxyl radicals, using the stable radicals TEMPO· (2,2,6,6-tetramethylpiperidine-1-oxyl radical), 4-oxo-TEMPO·/
- Wu, Adam,Mader, Elizabeth A.,Datta, Ayan,Hrovat, David A.,Borden, Weston Thatcher,Mayer, James M.
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supporting information; scheme or table
p. 11985 - 11997
(2009/12/08)
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- Process for the preparation of 4-substituted 2,2,6,6-tetramethyl-N-oxy and 2,2,6,6-tetramethyl-N-hydroxy piperidines
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Preparation of 4-substituted-piperidine-N-oxy compounds (II) or mixture of (II) and 4-substituted-piperidin-N-hydroxy-compounds (III) comprises oxidation of 4-substituted-piperidine compound [I] with hydrogen peroxide in the presence of alkali and/or ammonium hydrogen carbonate and optionally in the presence of solvents, where the reaction is carried out under the addition of Bronsted acid. Preparation of 4-substituted 2,2,6,6-tetramethyl-piperidine-N-oxy compounds of formula (II) or mixture of (II) and 4-substituted 2,2,6,6-tetramethyl-piperidin-N-hydroxy-compounds of formula (III) comprises oxidation of 4-substituted 2,2,6,6-tetramethylpiperidine compounds of formula [I] by hydrogen peroxide in the presence of alkali and/or ammonium hydrogen carbonate and optionally in the presence of solvents, where the reaction is carried out under the addition of Bronsted acid that possess an acid strength higher than the hydrogen carbonate. X+Y : O, cyclic ketals (containing groups of O-(CH2)2-O, O-CH(CH3)-CH2-O, O-CH(CH2OH)-CH2-O, O-(CH2)3-O or O-CH2-C(CH3)2-CH2-O) or open chain ketal (where X is O-R and Y is O-Ra); and R, Ra : CH3, CH2-CH3, CH2-CH2-CH3, CH(CH3)-CH3, CH2-CH2-CH2-CH3 or CH2-CH(CH3)-CH3. An independent claim is also included for a method for preparing (II) or mixture of (II) and (III) comprising oxidation of (I) with hydrogen peroxide in the absence of hydrogen carbonate, where the reaction is carried out optionally in the presence of solvents and addition of alkali- and/or ammonium dihydrogen phosphate as catalysts. [Image].
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Page/Page column 9; 11
(2008/06/13)
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- Process for preparing 4-substituted 2,2,6,6-tetramethylpiperidin-N-oxy and 2,2,6,6-tetramethylpiperidin-N-hydroxy compounds
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A process for preparing 4-substituted 2,2,6,6-tetramethylpiperidin-N-oxy compounds (II) or mixtures of (II) and 4-substituted 2,2,6,6-tetramethylpiperidin-N-hydroxy compounds (III) where X+Y can be O or can represent a cyclic ketal with the radicals or can represent an open-chain ketal in which X═O—R and Y═O—R′, where R and R′ can be identical or different and can each be CH3, CH2—CH3, CH2—CH2—CH3, CH(CH3)—CH3, CH2—CH2—CH2—CH3 and CH2—CH(CH3)—CH3, by oxidizing corresponding 4-substituted 2,2,6,6-tetramethylpiperidines (I) with hydrogen peroxide in the presence of alkali metal hydrogencarbonate and/or ammonium hydrogencarbonate and in the presence or absence of a solvent, in which the reaction is carried out with the addition of Br?nsted acids which have an acid strength greater than that of the hydrogencarbonate.
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Page/Page column 6-7
(2008/06/13)
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- EFFECT OF THE CHEMICAL STRUCTURE OF NITROXYL RADICALS ON THEIR REACTIVITY IN THE REACTION WITH HYDRAZOBENZENE AND TETRANITROMETHANE
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The reaction rate constants of reduction of stable radicals of different classes by hydrazobenzene in hexane at ca. 20 deg C, in the range of 0.4 - 5*103 M-1 sec-1, were determined; a single scale of the oxidative properties of stable nitroxyl radicals was constructed.The rate constants of oxidation of a series of nitroxyl radicals by tetranitromethane in aqueous medium at ca. 20 deg C, in the range of 0.06 - 10 M-1 sec-1, were determined.It was shown that the oxidative properties of the nitroxyl group decrease slightly with an increase in its reducing properties for nitroxyl radicals of the piperidine and imidazoline series in reactions with ascorbic acid and tetranitromethane in aqueous medium, respectively.
- Malievskii, A. D.,Koroteev, S. V.,Volodarskii, L. B.,Shapiro, A. B.
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p. 2331 - 2338
(2007/10/02)
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- DISSOCIATION ENERGY OF THE N-H BOND IN 2,6-DIARYL-4-PHENYL-1,2,3,4-TETRAHYDRO-SYM-TETRAZINES AND THE COMPARATIVE REACTIVITY OF SYM-TETRAZINYLS IN DEHYDROGENATION OF HYDRAZOBENZENE
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The equilibrium constants in the reactions of 2,6-diaryl-4-phenyl-1,2,3,4-tetrahydro-sym-tetrazines with 2,2,6,6-tetramethyl-4-oxopiperidin-1-oxyl in heptane were determined by spectrophotometric and ESR methods.The dissociation energies of the N-H bond is the sym-tetrazines were determined.Results are given which indicate that the substituents in the phenyl ring at the C6 and N2 atoms have effects substantially different and opposite in sign on the thermochemical value of the dissociation energy of the N-H bond in sym-tetrazines.The sym-tetrazines with donatingsubstituents at the C6 atom and accepting substituents at the nitrogen atom are characterized by the largest dissociation energy for the N-H bond.The kinetics of the dehydrogenation of hydrazobenzene by sym-tetrazinyls in acetonitrile were investigated.It was found that there is an inverse relationship between the activation energies of the reaction and the dissociation energy of N-H bond in sym-tetrazines.The reaction mechanism is discused.
- Misyura, A. V.,Polumbrik, O. M.,Markovskii, L. N.
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p. 381 - 387
(2007/10/02)
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- Acyl Nitroxides. Part 4. Estimation of OH Bond Dissociation Energies for N-t-Butylhydroxamic Acids
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E.s.r. spectroscopy has been used to determine the equilibrium constants for the hydrogen exchange reactions between N-t-butylhydroxamic acids and the stable piperidine N-oxyl (1); since the O-H bond strength in (1)-H is known, this gives an estimate of the O-H bond strengths in the hydroxamic acids.These are found to be stronger than those in dialkyl nitroxides and increase with increasing electron demand in the acyl group.
- Jenkins, Terence C.,Perkins, M. John
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p. 717 - 720
(2007/10/02)
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