- Synthesis and spectral comparison of electronic and molecular properties of some hydrazines and hydrazyl free radicals
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Continuing our work on hydrazyl free radicals, five triphenylhydrazine derivatives, one a new compound, were synthesized to compare the electronic and molecular properties of these compounds, study the influence of substituents on the phenyl rings, and compare their properties with the parent hydrazines and corresponding anions. These hydrazines demonstrate both acid-base and redox properties. The hydrazine proton can be removed by base, yielding the corresponding anion and both the hydrazines and their anions can be oxidized to the corresponding hydrazyl free radicals. ESR spectra confirmed their formation and X-ray crystallography of one compound confirmed their structures.
- Ionita, Petre,Lete, Cecilia,Madalan, Augustin,Matache, Mihaela,Patrascu, Bianca,Paun, Anca,Popescu, Codruta
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- Kinetic studies on the interactions of manganese-porphyrins with peracetic acid. Part 2. The influence of acetic acid and porphyrin substituents
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The one-electron oxidation of 1,1-diphenyl-2-picrylhydrazine (DPPH) and Zn-tetra-tert-butylphthalocyanine (PcZn) to the corresponding stable radical (DPP) and π-radical cation (PcZn+) with peracetic acid in acetonitrile-acetic acid has been studied, in the presence of MnIII complexes of meso-tetra(2,6-dichloro-4-R-phenyl)porphyrins (RTDCPPMnCl; R = CH3O, H, Br, Cl or NO2) as catalysts. The formation of a two-centre donor-acceptor complex of "catalyst-oxidant" type (adduct 'A') with rate constant k1 is the first stage of the reaction. The balance of the electron donating properties of the porphyrin ring and electron accepting properties of MnIII determines the formation of 'A', as shown by the independence of k1 of catalyst structure. The influence of added acetic acid on the UV-Vis spectra of RTDCPPMnX in CH3CN and on the oxidation rate of DPPH and PcZn evidenced that a molecule of AcOH is included in the internal co-ordination sphere of RTDCPPMnX and of the reaction intermediates. The rate constant k2 for the irreversible transformation of 'A' into an equilibrium mixture of MnV and MnIV oxo-species (established in Part 1) must thus refer to the acetic acid adducts of Mn-porphyrins {[RTDCPPMn(AcOH)](X)}. A non-linear dependence of log k2rel on σpara of the porphyrin substituents R has also been found. However, electron-withdrawing substituents are particularly effective for enhancement of the rate of formation of the high-valent oxomanganese species.
- Banfi, Stefano,Cavazzini, Marco,Pozzi, Gianluca,Barkanova, Svetlana V.,Kaliya, Oleg L.
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p. 879 - 885
(2007/10/03)
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- Manganese-porphyrins and -azaporphyrins as catalysts in alkene epoxidations with peracetic acid. Part 2. Kinetics and mechanism
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cis-Stilbene (cSt) and 1,1-diphenyl-2-picrylhydrazine (DPPH) were used as substrates for kinetic investigations of the catalytic system based on MnIII-porphyrins and peracetic acid in CH3CN. Catalysts employed were tetra-(2,6-dichlorophenyl)-porphyrinatomanganese chloride (TDCPPMnCl) 5, octanitrophthalocyaninatomanganese chloride (NO2PcMnCl) 6 and tetra(tert-butyl)-tetraazaporphyrinatomanganese chloride (TAPMnCl) 7. It was found that for all these catalysts the first step of the reaction mechanism is the formation of an adduct 'A' between the catalyst and AcOOH in a reversible way (k1/k-1), followed by an irreversible stage (k2) for the formation of Mnv-oxo species. The oxidative capability of the adduct 'A' was found to be dependent on the electronic structure of the catalyst, while the reactivity of Mn-oxo species is only slightly influenced by catalyst structure. The formation of the high-valent Mn-oxo species is the rate-determining step of alkene epoxidations as demonstrated by the same k2 value obtained with catalyst 6 in the epoxidation of cSt and trans-stilbene (tSt). Catalyst stability was found to be dependent on solvent polarity, CH3CN being the best reaction medium.
- Banfi, Stefano,Cavazzini, Marco,Coppa, Fausta,Barkanova, Svetlana V.,Kaliya, Oleg L.
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p. 1577 - 1583
(2007/10/03)
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- The rate-determining step in the epoxidation of alkenes by the cytochrome P-450 model manganese(III) porphyrin/hypochlorite
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Using low-temperature trapping experiments with 1,1-diphenyl-2-picrylhydrazine monitored by UV/Vis spectroscopy, it is shown that the rate-determining step in the epoxidation of alkenes by hypochlorite, catalysed by manganese(III) porphyrins, involves the formation of the active oxo-manganese species +.
- Made, A. W. van der,Groot, P. M. F. C.,Nolte, R. J. M.,Drenth, W.
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- Influence of Nitrogen Base Ligation and Hydrogen Bonding on the Rate Constants for Oxygen Transfer from Percarboxylic Acids and Alkyl Hydroperoxides to (meso-Tetraphenylporphinato>manganese(III) Chloride
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Equilibrium constants for axial ligation of imidazole (ImH), N-methylimidazole (N-MeIm), 4'-(imidazo-1-yl)-acetophenone (NAcPhIm), 2,6-lutidine (2,6-Py), and 3,4-lutidine (3,4-Py) with (meso-tetraphenylporphinato)manganese chloride ((TPP)MnIIICl) have been determined.The rates of oxygen atom transfer from percarboxylic acids and alkyl hydroperoxides (YOOH) to the manganese(III) porphyrin in the presence of varying concentrations of the nitrogen bases were determined.For this purpose, 2,2-diphenyl-1-picrylhydrazine (DPPH) was employed as a trap for the generated higher valent oxo-manganese porphyrin species.From the equilibrium and kinetic data, there was then calculated the second-order rate constants for oxygen atom transfer from YOOH compounds to the species (TPP)MnIIICl, TPP(Cl)MnIIIN, and TPP(Cl)MnIIIN2 (where N = ImH, N-MeIm, and 3,4-Py).Only the percarboxylic acids exhibit measurable rate constants for oxygen transfer to (TPP)MnIIICl, whereas alkyl hydroperoxides and percarboxylic acids transfer oxygen to the TPP(Cl)MnIIIN species.Of the species TPP(Cl)MnIIIN2, reaction with YOOH compounds is seen only when N is imidazole.This is attributed to an equilibrium of the unreactive bis axially ligated TPP(Cl)MnIII(ImH)2 with the reactive isomeric mono axial-ligated complex Cl(1-)...H-Im...H-Im...MnIIITPP.Nitrogen base ligation of (TPP)MnIIICl provides minimally a 1E3 increase in the rate constants for oxygen transfer in methylene chloride.Linear free-energy plots of the log of the second-order rate constants for oxygen transfer from YOOH vs. the pKa of YOH establish that β1g for oxygen transfer in which heterolytic O-O bond scission is rate-determining is large and negative.The value of β1g when oxygen transfer involves rate-determining homolytic O-O bond scission is small and negative.
- Yuan, Lung-Chi,Bruice, Thomas C.
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p. 1643 - 1650
(2007/10/02)
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- Preparation of 2,2-diaryl-1-picrylhydrazyls using potassium permanganate
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Potessium permanganate is used as a reagent for the oxidation of various 2,2-diaryl-1-picrylhydrazines to their corresponding hydrazyls.Thin-layer chromatography indicates complete oxidation of the hydrazine to free radical, unlike the case with PbO2 (the most widely used oxidant for this purpose).Several other advantages over previous oxidants used to produce the hydrazyls are offered.
- Brown, K. C.,Weil, J. A.
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p. 1836 - 1838
(2007/10/02)
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- ASYMMETRICAL NITROGEN-40; GEMINAL SYSTEM-26. N-CHLOROHYDRAZINES
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The factors determining the kinetic and thermodynamic stabilities of N-chlorohydrazines are discussed.Acyclic N-chlorohydrazines exist only as trialkyldiazenium chlorides 3a,b.Chlorination of 2-acyl-1,1-dimethylhydrazines 6a,b gave 1,4-diacyl-2,3-dimethylhexahydro-1,2,4,5-tetrazines 7a,b via hydrazyl radical intermediates, and chlorination of a 1-phenylpyrazolidin-5-one 8 gave phenylazoisovaleric esters 9a,b.Stable N-chlorohydrazines were obtained from bicyclic hydrazines; viz. the 2-chloro-1.2-diazabicyclo(2.2.2.)octan-3-one 12 and 7-chloro-1,7-diazabicyclo(2.2.1)heptane 16.The restricted inversion of N(7) in 16 and its 1-methyl quate rnary salt 21 were observed in the 13C-NMR spectra.The acyclic N-chlorohydrazinium salt 25 was isolated.
- Shustov, G. V.,Tavakalyan, N. B.,Kostyanovsky, R. G.
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p. 575 - 584
(2007/10/02)
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- MODEL COMPOUND STUDIES RELATED TO PEROXIDASES-II THE CHEMICAL REACTIVITY OF A HIGH VALENT PROTOHEMIN COMPOUND
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The chemical reactivity of the model analog to compound I of the peroxidases resulting from the reaction of "chelated protohemin" and m-chloroperbenzoic acid is examined.The model intermediate shows no H-atom abstraction or O insertion activity and substrate reactivity depends only on the E1/2 value of the substrate.A Marcus theory treatment of the available kinetic data for HRP suggests that the oxidative pathway for substrate oxidations is an outer-sphere electron transfer.From the results of the model catalyzed oxidation of 1,4-cyclohexadiene to benzene, an alternate mechanism for cytochrome P-450 catalyzed hydroxylations is suggested.
- Traylor, T. G.,Lee, William A.,Stynes, Dennis V.
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p. 553 - 568
(2007/10/02)
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- FEATURES OF THE REACTION OF 1,1-DIPHENYL-2-PICRYLHYDRAZINE WITH PEROXIDES CONTAINING A tert-BUTYL GROUP
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The reaction of 1,1-diphenyl-2-picrylhydrazine with unsymmetrical peroxides containing a tert-butyl group gives rise to decomposition of the latter at the O-O bond.The reaction occurs with the formation of 1,1-diphenyl-2-picrylhydrazyl, which can in turn enter into reaction with the peroxides.The kinetic parameters of the accumulation of 1,1-diphenyl-2-picrylhydrazyl in various solvents were obtained.A mechanism for the reaction is proposed.
- Kucher, R. V.,Luk'yanenko, L. V.,Turovskii, A. A.
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p. 734 - 739
(2007/10/02)
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- Measurements of active site concentrations at rhodium, osmium, iridium, and platinum surfaces by 1,1- diphenyl- 2- picrylhydrazine oxidation in the liquid phase, and by carbon monoxide chemisorption from the gas phase
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The reaction at room temperature between diphenylpicrylhydrazine and chemisorbed oxygen may be used to determine, in a simple manner, active surface site concentrations for rhodium, iridium, and platinum powders. The method is not suitable for osmium. A f
- MOYES RB,WELLS PB,BARON K,COMPSON K,GRANT J,HESELDEN R
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p. 224 - 227
(2007/11/03)
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