35822-90-3Relevant academic research and scientific papers
ESR Spin-Trapping Study of the Radicals Produced in NOx/Olefin Reactions. A Mechanism for the Production of the Apparently Long-Lived Radicals in Gas-Phase Cigarette Smoke.
Pryor, William A.,Tamura, Masamitsu,Church, Daniel F.
, p. 5073 - 5079 (1984)
Gas-phase cigarette smoke contains high concentrations of both oxygen- and carbon-centered free radicals.We have detected these radicals using several variations of the electron spin resonance (ESR) spin-trapping technique, including the use of spin traps in the solid state, to show that the radicals are trapped directly from the gas phase.These gas-phase radicals can still be trapped from gas-phase smoke that is more than 5 min old, a result that is clearly inconsistent with the highly reactive nature of oxygen- and carbon-centered radicals.To rationalize this apparent paradox, we hypothesize that free radicals are continuously produced and destroyed in cigarette smoke and exist in a steady state.We suggest that one mechanism by which radicals can be formed involves the slow oxidation of the relatively unreactive nitric oxide (which acts as a "radical reservoir") to the much more reactive nitrogen dioxide.Nitrogen dioxide can then react with a number of the species that are present in smoke to produce the radicals that we detect.As a model, we have studied the reactions of NO/air mixtures with unsaturated hydrocarbons.Isoprene is one of the most abundant species in smoke and is known to be very reactive toward NO2; therefore we have studied the nature of the radicals that can be spin trapped from gaseous mixtures of NO, isoprene, and air.We find that the NO/air/isoprene model system gives essentially the same types of radicals (oxygen and carbon centered) as does cigarette smoke.We have also studied the gas-phase reactions of NO2 with several small olefins and 1,3-butadiene and find evidence for peroxyl radical intermediates.In solution, NO2 reacts with isoprene much faster than it does with the spin-trap phenyl-tert-butylnitrone (PBN).We find that NO2 oxidizes PBN to benzoyl tert-butyl nitroxide and propose a mechanism for this reaction.
Oxidative cleavage of CH3 and CF3 radicals from BOXAM nickel complexes
Klein, Axel,Vicic, David A.,Biewer, Christian,Kieltsch, Iris,Stirnat, Kathrin,Hamacher, Claudia
, p. 5334 - 5341 (2012/11/13)
Oxidation of the nickel complexes [(BOXAM)Ni(R)] (HBOXAM = bis((4-isopropyl-4,5-dihydrooxazol-2-yl)phenyl)amine) with R = CF3, CH3, Cl leads to the corresponding radical cationic complexes, which rapidly undergo homolytic Ni-R bond s
Titanium tetra-tert-butoxide-tert-butyl hydroperoxide oxidizing system: Physicochemical and chemical aspects
Stepovik,Gulenova,Martynova,Mar'Yasin,Cherkasov
, p. 266 - 276 (2008/09/20)
The reaction of titanium tetra-tert-butoxide with tert-butyl hydroperoxide (1: 2) (C6H6, 20 C) involves the steps of formation of the titanium-containing peroxide (t-BuO)3TiOOBu-t and peroxytrioxide (t-BuO)3TiOOOBu-t. The latter decomposes with the release of oxygen, often in the singlet form, and also homolytically with cleavage of both peroxy bonds. The corresponding alkoxy and peroxy radicals were identified by ESR using spin traps. The title system oxidizes organic substrates under mild conditions. Depending on the substrate structure, the active oxidant species can be titanium-containing peroxide, peroxytrioxide, and oxygen generated by the system.
Alkoxyamines of stable aromatic nitroxides: N-O vs. C-O bond homolysis
Gigmes, Didier,Gaudel-Siri, Anouk,Marque, Sylvain R. A.,Bertin, Denis,Tordo, Paul,Astolfi, Paola,Greci, Lucedio,Rizzoli, Corrado
, p. 2312 - 2326 (2007/10/03)
A series of stable 2,2-disubstituted 3-(phenylimino)indol-1-oxyls, the alkoxyamines 3, were prepared, characterized, and tested as possible candidates in controlled radical polymerization (CRP). The sturctures of 3d and 10 were additionally solved by X-ra
Fluoro spin adducts and their modes of formation
Eberson, Lennart,Persson, Ola
, p. 893 - 898 (2007/10/03)
The reactions of two fluorinating reagents, XeF2 and N-fluorodibenzenesulfonamide [(PhSO2)2N-F], with several spin traps have been investigated. In dichloromethane, the strong oxidant XeF2 cleanly gives fluoro spin adducts with N-tert-butyl-α-phenylnitrone (PBN) or 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) according to a mechanism mediated by the radical cation of the spin trap. In both cases, further fluorination takes place with replacement of the a hydrogen by fluorine. The much weaker oxidant (PhSO2)2N-F reacts with PBN or DMPO in dichloromethane giving both the fluoro adduct and an adduct formally derived from an N-centred radical, assigned the structure of PhSO2N(F)-PBN? or (PhSO2)2N-DMPO?, respectively. This type of reaction proceeds by a version of the Forrester-Hepburn mechanism, in which an acid HA, in this case HF, initially adds to the nitrone function to give a hydroxylamine derivative which is oxidized by (PhSO2)N-F giving the fluoro spin adduct, a proton and the highly labile radical anion (PhSO2)2N-F?-. By decomposition of the latter to PhSO2(F)N- and PhSO2?, conditions are set up for propagation of the reaction by a new molecule of HA [now PhSO2(F)NH] and thus formation of the PhSO2(F)N spin adduct.
Mass spectrometry and electron paramagnetic resonance study of free radicals spontaneously formed in nitrone-peracid reactions
Sang, Hong,Janzen, Edward G.,Lewis, Brian H.
, p. 2358 - 2363 (2007/10/03)
Reactions of spin traps (C-phenyl N-tert-butyl nitrone (PBN) and 5,5-dimethyl-2-phenyl-1-pyrroline N-oxide (2-Ph-DMPO)) with peracids have been investigated by both mass spectrometry (MS) and electron paramagnetic resonance (EPR). The peracids m-chloroperbenzoic acid, perbenzoic acid, and perpropionic acid, which can be considered models of biological peracids produced during lipid peroxidation, were found to react with spin traps to spontaneously produce significant amount of aminoxyl radicals. The radical products, as well as the nonradical products were detected and their structures identified by EPR and/or MS. Mechanisms for the formation of these products are proposed.
Spin trapping of fluoroalkyl radicals
Gille, Lars,Stoesser, Reinhard
, p. 191 - 194 (2007/10/02)
The formation of fluoroalkyl radicals in liquid chlorofluorocarbons (CF2Cl-CFCl2, CFCl3, CFCl2-CH3, CHF2-CF2-CF2Cl, CF3-CFH-CF3 and CCl4) has been investigated by means of the spin trapping technique and ESR spectroscopy.It is shown that the primary fluoroalkyl radicals which were generated in these compounds by ionising radiation are preferably formed by bond cleavage at carbon atoms attached to one fluorine atom.Besides the liberation of chlorine atoms in chlorine-containing compounds, in CHF2-CF2-CF2Cl and CF3-CFH-CF3 fluorine atoms were also detected.By comparison of radicals formed from γ-irradiated CF2Cl-CFCl2 (CFC-113) and from CF2Cl-CFClI or CF2I-CFCl2 by zinc reduction, it was demonstrated that in CFC-113 both .CF2-CFCl2 and .CFCl-CF2Cl radicals are formed, whereas in iodine-containing homologues the formation of one species is favoured. - Keywords: Spin trapping; Fluoroalkyl radicals; ESR spectroscopy; γ-Irradiation; Zinc reduction; Phenyl-tert-butylnitrone
Mechanistic Studies by Electron Paramagnetic Resonance Spectroscopy on the Formation of 2-(N-Chloroimino)-5,5-dimethylpyrrolidine-1-oxyl Radical from 5,5-Dimethyl-1-pyrroline 1-Oxide and Hypochlorite-Treated Ammonia
Bandara, B. M. Ratnayake,Hinojosa, Oscar,Bernofsky, Carl
, p. 1642 - 1654 (2007/10/02)
Mixtures of ammonium ion (NH4(1+)) or ammonia (NH3), hypochlorous acid (HOCl), and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) gave the radical 2-(N-chloroimino)-5,5-dimethylpyrrolidine-1-oxyl (1).The first step in the formation of 1 was the reaction of HOCl and NH4(1+) to provide ammonia chloramines: monochloramine (NH2Cl), dichloramine (NHCl2), and trichloramine (NCl3).Chloramine composition and the formation of 1 were dependent on pH, the ratio of NH4(1+) to HOCl, and, at acidic pH, on the concentration of chloride in the medium.Conditions were chosen to isolate the individual chloramines in solution for further study.NCl3 and DMPO gave 1; however, NHCl2 and NH2Cl required additional oxidants such as HOCl or PbO2 to produce 1.Studies with 15N-labeled chloramines confirmed that NHCl2 and NH2Cl reacted with DMPO to form N-chloro intermediates that yielded 1 upon subsequent oxidation.Light had no effect on the formation of 1, and UV irradiation did not enhance the EPR signal intensity but caused rapid decay, indicating that radical intermediates of ammonia chloramines were not involved.The mechanism of formation of 1 appeared to involve temporary attachment of chloramine Cl to the nitroxide oxygen of DMPO which activated its β-carbon for nucleophilic addition of the chloramine N.Subsequent N-chlorination and/or dehydrochlorination, depending on the reactive chloramine, would then provide 1.However, nucleophilic addition of H2O to the activated β-carbon of DMPO was competitive because 5,5-dimethyl-2-hydroxypyrrolidine-1-oxyl (DMPO-OH) or 5,5-dimethyl-2-pyrrolidone-1-oxyl (DMPOX) radicals were sometimes observed as minor products along with 1.Analogous chloroimine radicals were not obtained from the reaction of ammonia chloramines with 3,3,4,4-tetramethyl-1-pyrroline 1-oxide (M4PO) and N-tert-butyl-α-phenylnitrone (PBN), although their 2-oxo nitroxyl derivatives and hydroxyl adducts were formed as radical products suggesting that nucleophilic addition of H2O was dominant with these nitroxides.
Spontaneous Free-Radical Formation in Reactions of m-Chloroperbenzoic Acid with C-Phenyl-N-tert-butylnitrone (PBN) and 3- or 4-Substituted PBN's
Janzen, Edward G.,Lin, Chiou-Rong,Hinton, Randall D.
, p. 1633 - 1635 (2007/10/02)
A molecular reaction between m-chloroperbenzoic acid and C-phenyl-N-tert-butylnitrone (PBN) produces significant amounts of aminoxyl radicals assigned to the m-chlorobenzoyloxyl adduct of PBN and benzoyl-tert-butylaminoxyl.
The Mechanistic Diversity of the Thermal and Photochemical Decomposition of Bis(phenylphosphonoyl)Peroxides: Concerted Polar, Homolytic and Electron-Transfer Processes. On the Reactivity of (Phenylphosponoyl)oxyl Radicals
Korth, Hans-Gert,Lommes, Petra
, p. 2419 - 2438 (2007/10/02)
The thermal and photochemical decomposition of the first bis(phenylphosphonoyl)peroxides, dioxybis (5), and dioxybis (6) has been studied in various solvents by 1H-, 13C-, and 31P-NMR spectroscopy, laser flash photolysis (LFP), and ESR spin-trapping experiments.Kinetic studies reveal at 20 deg C a ca. 270 times slower thermal decay for 5 than for 6, which primarily results from a lower A factor rather than differences in the activation energies.The thermal decay of 5 occurs predominantly by a novel, presumably concerted polar rearrangement with formation of a thermally unstable, mixed phosphonoyl-phosphoryl anhydride.Photolysis of 5 induces homolytical cleavage of the peroxy bond with release of oxyl radicals 7.Radical 7 is characterized by a broad, transient UV/Vis absorption spectrum in the 400 to >700 nm range (λmax ca. 580 nm), as has been demonstrated by 248-nm LFP of 5 in acetonitrile solution.The short lifetime of this absorption indicates an extremely high reactivity (in hydrogen abstraction and addition) of this electrophilic radical.The thermal and photochemical decomposition of peroxide 6 leads to a virtually identical product distribution, suggesting O-O bond cleavage to be the major initial reaction under both conditions.LFP at 248 and 308 nm of a solution of 6 in acetonitrile initially produces a weak, broad absorption at ca. 500 nm and stronger bands at 280 and 400 nm.The highly transient 500-nm absorption is assigned to the oxyl radical 8, the other bands are attributed to the phosphonoyloxy-substituted benzene radical cation 8Z.The formation of this species can be explained in terms of electron transfer in the first-formed oxyl radical 8 and/or the intact peroxide 6, followed by cleavage of the peroxy bond.The decay of 8Z is accompanied by the build-up of the absorption spectrum of a 1,4-dioxy-substituted biphenyl radical cation.Key Words: Oxyl radicals / Phosphonoyl peroxides / Laser flash photolysis /ESR-Spin trapping / Electron transfer
