- Trans-1,2-Disiloxybenzocyclobutene, an adequate partner for the auto-oxidation: EPR/spin trapping and theoretical studies
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The auto-oxidation of trans-1,2-disiloxybenzocyclobutene 1 was found to be very efficient, giving endo-peroxide 7 in quantitative yield. Each step of the mechanism of spin-forbidden addition of triplet oxygen O2( 3Σg) was
- Drujon, Jean,Rahmani, Raphael,Heran, Virginie,Blanc, Romain,Carissan, Yannick,Tuccio, Beatrice,Commeiras, Laurent,Parrain, Jean-Luc
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- Intramolecular Hydrogen Atom Transfer in Aminyl Radical at Room Temperature with Large Kinetic Isotope Effect
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We report a large kinetic isotope effect at 298 K, kH/kD ≈ 150, associated with an intramolecular 1,5-hydrogen atom transfer (1,5-HAT) in the decay of a PEGylated carbazyl (aminyl) radical in solution. The experimental observations surprisingly combine the hallmarks of tunneling, including large KIEs and unusual activation parameters, with linear Arrhenius and Eyring plots over an exceptionally wide temperature range of 116 K.
- Wang, Ying,Olankitwanit, Arnon,Rajca, Suchada,Rajca, Andrzej
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- Kinetic model of radical reaction in plastic crystals
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The kinetic features of diffusion-depended model process of photoinduced nitroxide formation from 2-methyl-2-nitrosopropane in a number of plastic crystals (PC: cyclohexane, cyclohexanol, cyclohexanon, cyclopentanon, 1,1,1-trichlorethane, tert-butylchloride, tert-butylamine, tert-butanol, benzene have been studied by ESR. The kinetic model that relates the nitroxide formation quantum yield with parameters of Lennard - Jones' potentials and thermodynamic properties of PC is proposed.
- Morosov,Shabatina,Batyuk,Sergeev
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- Photoactivatable platinum anticancer complex can generate tryptophan radicals
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l-Tryptophan (Trp), melatonin (MLT) and the Trp-peptide pentagastrin quenched the formation of azidyl radicals generated on irradiation of the anticancer complex trans,trans,trans-[Pt(pyridine)2(N3)2(OH)2] with visible light, giving rise to C3-centred indole radicals which were characterized for Trp and MLT using an EPR spin-trap; indole, together with azidyl and hydroxyl radicals, have potential roles in a multitargeting mechanism of action against resistant cancers.
- Vallotto, Claudio,Shaili, Evyenia,Shi, Huayun,Butler, Jennifer S.,Wedge, Christopher J.,Newton, Mark E.,Sadler, Peter J.
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- Mechanism of SmI2 Reduction of 5-Bromo-6-oxo-6-phenylhexyl Methanesulfonate Studied by Spin Trapping with 2-Methyl-2-nitrosopropane
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The radical formed by reduction of 5-bromo-6-oxo-6-phenylhexyl methanesulfonate, an α-bromoketone, with SmI2 was spin trapped with 2-methyl-2-nitrosopropane. Electron paramagnetic resonance spectra of the spin adduct and the adduct formed in the analogous reaction with selectively deuterated substrate identify the radical intermediate in this SmI2 reduction as a carbon-centered radical. This result supports the proposal that the formation of reactive Sm-enolates arises from reduction of the carbon-bromine bond rather than a ketyl radical anion.
- Aretz, Christopher D.,McPeak, Joseph E.,Eaton, Gareth R.,Eaton, Sandra S.,Cowen, Bryan J.
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- Reactions of Ruthenium Formyl and Related Complexes with Nitroxide Spin Traps
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Reactions of the complexes trans- (dppe=Ph2PCH2CH2PPh2), cis- (dppm=Ph2PCH2PPh2), or trans- with ButNO give But2NO. and trans-tNO)(CO)(P-P)2>.+ (M=Ru, P-P=dppe or dppm; M=Os, P-P=dppe), the structures of which have been elucidated by e.s.r. and labelling (13C, 2H) studies. cis- or trans-+ gives only But2NO., whilst trans-2+ gives a mixture of trans-tNO)PPh2>>.2+ and a radical with the trap bound to a carbonyl carbon atom.The decomposition products of cis-+ gave a radical with the trap bound to the back-bone carbon atom of a chelating dppm ligand, whilst dppe and dppm both give radicals where the ButNO group is bound to a phosphorus atom.The mechanisms of some of these reactions are discussed.
- Smith, Garry,Sutcliffe, Leslie H.,Cole-Hamilton, David J.
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- NO spin trapping and EPR studies on the photochemistry of aliphatic aldehydes
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Radicals, such as acyl, hydrated acyl, alkyl and ketyl radicals, from aliphatic aldehyde photochemistry were detected by NO spin trapping and EPR techniques. Deuterium effects on EPR spectra and the generation of radicals by 2-amido-2-propyl radical attack on substrate molecules in aqueous solution via hydrogen-atom abstraction were applied to identify radicals produced photochemically from aldehydes. Aliphatic aldehydes used in the present investigation were formaldehyde, acetaldehyde, acetaldehyde-d4, propionaldehyde, isobutyraldehyde, isopentanal and tert-pentanal. Possible reaction mechanisms are suggested. Copyright
- Wang, Fan,Lei, Liandi,Wu, Longmin
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- A Free-Radical-Promoted Site-Specific Cross-Dehydrogenative-Coupling of N-Heterocycles with Fluorinated Alcohols
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A C-C formation of an electron-rich N-heterocycle with fluorinated alcohol is developed. Through this radical-triggered cross-dehydrogenative coupling strategy, a wide range of useful building blocks such as C3 hydroxyfluoroalkylated indoles and pyrroles can be site-specifically synthesized. Mechanistic studies indicate a single-electron-transfer initiated radical cycle would be involved.
- Xu, Zhengbao,Hang, Zhaojia,Chai, Li,Liu, Zhong-Quan
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supporting information
p. 4662 - 4665
(2016/09/28)
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- An EPR study of the radical addition to 3-nitropentan-2-one as an archetype of α-carbonylnitroalkanes
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Carbon, silicon, germanium, tin and lead-centered radicals were reacted with 3-nitropentan-2-one and 3-nitropentan-2-ol inside the cavity of an electron paramagnetic resonance spectrometer. In all cases, selective addition to the nitrogroup was observed with detection of the corresponding oxynitroxide radicals. In the case of the carbonyl substrate, alkyl acyl nitroxides were also detected because of α-photocleavage. The oxynitroxides decayed with a first order kinetics via fragmentation of the carbon-nitrogen bond (denitration). Unexpectedly, the activation parameters were fairly similar to those previously reported for the corresponding tert-butyl oxynitroxides and almost independent from the presence of a carbonyl or a hydroxyl group on the carbon adjacent to the one bearing the nitrogroup. Copyright
- Campredon, Mylene,Alberti, Angelo
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p. 289 - 297
(2014/06/09)
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- The photoreactions of simple amides with NO. Gaining insight into radical bio-damages through an EPR case study
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Eight simple amides have been subjected to UV irradiation in the presence of either MNP or NO. In all cases radical species were generated: these were detected by means of EPR spectroscopy in the form of different nitroxides resulting from the trapping of the primary radicals. NO acted as a double spin trap, scavenging a radical to afford a diamagnetic nitroso derivative that in turn acted as trap towards another radical unit. As amido-groups are present in components of skin tissue and may be present in many therapeutic or cosmetic products used as skin sunscreen, and NO is a ubiquitous endogenous reactive species, the nitroxides detected in the present studies might participate in radical processes triggered by sun exposure and resulting in damages, even severe, of biological tissues.
- Alberti, Angelo,Grossi, Loris,MacCiantelli, Dante
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supporting information; experimental part
p. 2662 - 2670
(2012/05/04)
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- Reactive ligands in radical processes catalyzed by copper complexes
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The effect of the reactivity of donor ligands on the catalytic properties of copper complexes in the oxidative dimerization of mercaptans is considered. Catalytic compositions containing metal complexes in an excess of organic reagent ligands, which can show pronounced reductive properties (aromatic amines) or, on the contrary, oxidative properties (dimethyl sulfoxide) toward substrates, exhibit the greatest activity. In the course of the oxidation of mercaptans catalyzed by copper complexes, redox reactions accompanied by not only a change in the oxidation state of the metal but also the direct interaction of a substrate with an organic donor occur. In the presence of aromatic amines, the coupled oxidation of thiols and amines occurs, whereas dimethyl sulfoxide participates in the reaction as an oxidizing agent.
- Tarkhanova,Gantman
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scheme or table
p. 82 - 88
(2011/05/19)
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- Spin trapping of radical intermediates generated by the oxidation of substituted 4-methylphenols
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A series of substituted 4-methylphenols 1 and 2 was oxidized with PbO 2 in the presence of nitroso compounds 3-10. The formation of adducts of benzyl radicals with the nitroso spin traps in the reaction mixture was established, suggesting the abstraction of an H-atom from the methyl substituent of 1 or 2. In the consecutive steps, the adducts underwent a further rearrangement to the corresponding nitrones. When the starting phenol contained bulky tBu groups in ortho-position (see 2,6-di(tert-butyl)-4- methylphenol (1a)), the stable 2,6-di(tert-butyl)-4R-phenoxy radicals (R=-CH=N+(O-)-X) were detected as the final radical products. The indirect evidence of nitrones in the reaction mixture was performed in one case by the reaction with a RO2 radicals. Copyright
- Majzlik, Petr,Omelka, Ladislav,Superatova, Renata,Holubcova, Petra
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experimental part
p. 1260 - 1268
(2011/10/09)
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- EPR/Spin-trapping study of free radical intermediates in the photolysis of trifluoromethyl ketones with initiators
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Photolysis of trifluoromethyl ketones (TFMKs) 1a-1e versus the non-fluorinated ketones 2a-2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2-methyl-2-nitrosopropane (MNP) and 2,4,6-tritert- butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t-butylperoxide, short-chain TFMKs, such as 1,1,1-trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long-chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one α-methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a γ-hydrogen to the carbonyl group. Copyright
- Rosa, Esmeralda,Guerrero, Angel,Bosch, M. Pilar,Julia, Luis
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scheme or table
p. 198 - 204
(2010/07/07)
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- Tuning of the thermochemical and kinetic properties of ascorbate by its local environment: Solution chemistry and biochemical implications
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Ascorbate (vitamin C) is a ubiquitous biological cofactor. While its aqueous solution chemistry has long been studied, many in vivo reactions of ascorbate occur in enzyme active sites or at membrane interfaces, which have varying local environments. This report shows that the rate and driving force of oxidations of two ascorbate derivatives by the TEMPO radical (2,2′,6,6′-tetramethylpiperidin-1-oxyl) in acetonitrile are very sensitive to the presence of various additives. These reactions proceed by the transfer of a proton and an electron (a hydrogen atom), as is typical of biological ascorbate reactions. The measured rate and equilibrium constants vary substantially with added water or other polar solutes in acetonitrile solutions, indicating large shifts in the reducing power of ascorbate. The correlation of rate and equilibrium constants indicates that this effect has a thermochemical origin rather than being a purely kinetic effect. This contrasts with previous examples of solvent effects on hydrogen atom transfer reactions. Potential biological implications of this apparently unique effect are discussed.
- Warren, Jeffrey J.,Mayer, James M.
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supporting information; experimental part
p. 7784 - 7793
(2010/08/06)
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- 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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- Entropy control of the cross-reaction between carbon-centered and nitroxide radicals
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Absolute rate constants for the cross-coupling reaction of several carbon-centered radicals with various nitroxides and their temperature dependence have been determined in liquids by kinetic absorption spectroscopy. The rate constants range from 5 M-1 s-1 to 2.3 × 109 M-1 s-1 and depend strongly on the structure of the nitroxide and the carbon-centered radical. Grossly, they decrease with increasing rate constant of the cleavage of the corresponding alkoxyamine. In many cases, the temperature dependence shows a non-Arrhenius behavior. A model assuming a short-lived intermediate that is hindered to form the coupling product by an unfavorable activation entropy leads to a satisfactory analytic description. However, the behavior is more likely due to a barrierless single-step reaction with a low exothermicity where the free energy of activation is dominated by a large negative entropy term.
- Sobek,Martschke,Fischer
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p. 2849 - 2857
(2007/10/03)
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- Inhibiting polymerization of vinyl aromatic monomers
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When a nitroxyl compound is heated in an oxygen-free atmosphere with a vinyl aromatic monomer at 50-140 DEG C. for up to 60 days, it forms an activated inhibitor mixture which is superior to the nitroxyl compound itself in preventing the premature polymerization of a vinyl aromatic monomer during its processing and purification.
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- Polymerization inhibition of acrylates using blends of nitroxides
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Ethylenically unsaturated carboxyl monomers, such as acrylic or methacrylic acid or their esters, are protected from premature polymerization during manufacture and storage in the presence or absence of water by the incorporation therein of an effective stabilizing amount of a blend two or more nitroxides. Some of these blends provide synergistic stabilization efficacy much superior to the stabilization results obtained by use of either nitroxide alone.
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- Reaction between dinitroamide lon and the radical cation of N-tert-butyl-α-phenylnitrone. Formal elimination of nitrous acid from a spin adduct
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Dinitroamide ion was oxidized at a potential of 2.3-2.4 V and reduced at - 0.4 V (Ag/AgCl reference electrode). The photochemical oxidation of a solution of a dinitroamide salt and the spin trap. N-tert-butyl-α-phenylnitrone (PBN). in acetonitrile or dichloromethane gave rise to a weak 3×5 lines EPR spectrum, assigned to the formal spin adduct of dinitroamino radical and PBN, (NO2)2 N-PBN'. The reaction is suggested to involve oxidation of PBN to its radical cation, followed by capture of dinitroamide ion by the latter. The thermal oxidation of similar solutions gave rise to a different, much more intense EPR spectrum, the hyperfine splitting constants of which showed the presence of three different nitrogens and the absence of the α-hydrogen of PBN. The spectrum was assigned to O2N-N=C(Ph)-N(O')(But), formally derived from the dinitroamino spin adduct by elimination of nitrous acid. Mechanistically, this transformation presumably occurs by one-electron oxidation of (NO2J2N-PBN'. followed by loss of a proton and NO2 from the nitrosonium ion intermediate formed. Acta Chemica Scandinavica 1998.
- Eberson, Lennart
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p. 207 - 211
(2007/10/03)
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- Spin adducts from the reaction between N-phenyl-α-tert-butylnitrone (PBN) and activated olefins. A facile pathway converting PBN into 2-methyl-2-nitrosopropane (MNP)
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N-Phenyl-α-tert-butylnitrone (PBN) reacts with activated olefins RCH=CHR, such as maleimides, maleic anhydride or diethyl maleate, with formation of two types of persistent spin adducts giving characteristic EPR spectra, denoted types A and B. Spin adducts with type A spectrum were formed photochemically and identified as reductive coupling products between the olefin and PBN, RCH2CH(R)-PBN.. Spin adducts with type B spectra were formed photochemically and/or thermally and were identified as reductive coupling products RCH2CH(R)-N(O.)But between the olefin and a degradation product of PBN, 2-methyl-2-nitrosopropane (MNP, t-BuNO). The conversion of PBN to t-BuNO was studied for a compound with an exceedingly reactive nitrogen-nitrogen double-bond, namely 4-phenyl-4H-1,2,4-triazoline-3,5-dione (PTAD). In this case, a 74% yield of t-BuNO was obtained in a short period of time; α,N-diphenylnitrone reacted similarly to give nitrosobenzene. The reaction between PBN and an activated olefin was assumed to occur analogously, either via the initial formation of a 1,3-dipolar cycloadduct or some parallel reaction involving attack of the electrophilic olefin at the PBN α-carbon. The 1,3-dipolar cycloadduct between PBN and N-phenylmaleimide exhibited favourable initiator properties for living polymerization of styrene. A new type of spin adduct, RCH(But)CH(R)-N(O.)But, was prepared by the photochemical reaction between an activated olefin and t-BuNO. This reaction presumably proceeds by photocleavage of t-BuNO to NO and t-Bu., the latter reacting with the activated olefin to give a transient radical, RCH(But)CH.(R), which is trapped by t-BuNO. Acta Chemica Scandinavica 1998.
- Eberson, Lennart,Persson, Ola
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p. 1081 - 1095
(2007/10/03)
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- On the reported intermediacy of vinyl radicals in spontaneous polymerization: An ESR-spin trapping study and its significance for the bond forming initiation theory
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Deuterated isopropyl vinyl sulfides and diethyl fumarate were synthesized and employed in a re-investigation of the mechanism of initiation of spontaneous polymerization of these comonomers by means of spin- trapping/ESR spectroscopy. Previous radical spin-trapping studies had been interpreted as indicating the involvement of vinyl radicals. While our studies produced data substantially in agreement with the previous study, it must be noted that the date are not consistent with literature data for other vinyl radicals. Accordingly, results from both spin-trapping/ESR studies me inconsistent with involvement of vinyl radical intermediates, but are consistent with initiation by tetramethylene diradicals.
- Mash, Eugene A.,Korth, Hans-Gert,DeMoss, Suzanne M.
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p. 15297 - 15320
(2007/10/03)
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- Fluoro spin adducts and their modes of formation
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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.
- Eberson, Lennart,Persson, Ola
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p. 893 - 898
(2007/10/03)
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- Generation of acyloxyl spin adducts from N-tert-butyl-a-phenylnitrone (PBN) and 4,5-dihydro-5,5-dimethylpyrrole 1-oxide (DMPO) via nonconventional mechanisms
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The reaction between N-tert-butyl-α-phenylnitrone (PBN) and carboxylic acids has been studied Two mechanisms are discernible: the generation of PBN+ by oxidation of PBN with a photochemically produced excited state [from either 2,4,6-tris(4-methoxyphenyl)pyrylium ion 2+ or tetrachlorobenzoquinone 4], followed by reaction with RCOOH, or the addition of RCOOH to PBN to give a hydroxylamine derivative, followed by thermal oxidation by a weak oxidant. The latter sequence is the Forrester-Hepburn mechanism. In this mechanism, neither 2+ nor 4 is effective as an oxidant, whereas bromine could be used. Thus only oxidants with redox potentials ≥ 0.1 (SCE) are reactive enough to oxidize the intermediate hydroxylamine. This behaviour is in agreement with the redox reactivity of hydroxylamines. For the cylic nitrone, 4,5-dihydro-5,5-dimethylpyrrole 1-oxide (DMPO), acyloxyl spin adducts have been prepared by the photochemical route. The reaction between dibenzoyl peroxide and PBN to give PhCOO-PBN is not cataysed by added PhCOOH. It could be shown that the rate of formation of PhCOO-PBN is compatible with the rate of thermal decomposition of dibenzoyl peroxide. Thus dibenzoyl peroxide does not support the Forrester-Hepburn mechanism, in agreement with its redox potential of ca. -0.2 V.
- Eberson, Lennart,Persson, Ola
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p. 1689 - 1696
(2007/10/03)
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- Method for inhibiting premature polymerization of vinyl aromatic monomers
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Nitroxyl inhibitors in combination with some oxygen reduce the premature polymerization of vinyl aromatic monomers during the manufacturing processes for such monomers. Even small quantities of air used in combination with the nitroxyl inhibitors result in vastly prolonged inhibition times for said monomers.
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- Mass spectrometry and electron paramagnetic resonance study of free radicals spontaneously formed in nitrone-peracid reactions
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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.
- Sang, Hong,Janzen, Edward G.,Lewis, Brian H.
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p. 2358 - 2363
(2007/10/03)
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- Reactions of N-nitrosodiphenylamine with Grignard reagents. A convenient synthesis of diaryl- and dialkyl nitroxyls
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N-nitrosodiphenylamine reacts with Grignard reagents forming symmetric dialkyl- or diarylhydroxylamines which are quantitatively converted into the corresponding nitroxyls by lead dioxide oxidation.
- Cardellini,Greci,Tosi
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p. 201 - 207
(2007/10/02)
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- Reactions of Tris(trimethylsilyl)silyl Radicals with Nitroalkanes. EPR, Kinetic, and Product Studies
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The radical-initiated reaction of tris(trimethylsilyl)silane with a variety of aliphatic nitro derivatives has been investigated.This silane, which for many applications is a valid alternative to tributyltin hydride, is unable to reduce tertiary nitroalkanes to the corresponding hydrocarbons.EPR results, as well as kinetic and products studies, have shown that this "anomalous" behavior is due to the fact that the nitroxide adducts formed by addition of tris(trimethylsilyl)silyl radicals to the nitro compounds fragment preferentially at the nitrogen-oxygen bond ratherthan at the carbon-nitrogen bond as in the analogous tributyltin adducts.The resulting silyloxy radical, (Me3Si)3SiO, undergoes a fast rearrangement (k 107 s-1 at room temperature) with migration of a Me3Si group from silicon to oxygen to give (Me3Si)2SiOSiMe3 which adds to the nitro compound affording a secondary nitroxide adduct.The kinetics of the decay of both primary and secondary adducts to nitromethane has been studied over a wide range of temperatures.With tertiary nitroalkanes persistent aminyl radicals, RNOSi(SiMe3)3, have also been detected.
- Ballestri, Marco,Chatgilialoglu, Chryssostomos,Lucarini, Marco,Pedulli, Gian Franco
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p. 948 - 952
(2007/10/02)
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- The reaction of 5-cyclohexadienyl)Fe(CO)3>+BF4- with 2-methyl-2-nitrosopropane: an unexpected oscillating reaction
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The reaction of 2-methyl-2-nitrosopropane with the organometallic cation 5-cyclohexadienyl)trycarbonyliron>+ yields the bis(t-butyl)nitroxide radical which is detected by ESR spectroscopy.The intensity of the ESR signal varies in an oscillatory manner with time and the ESR silent period between oscillations ranges from 15 minutes to one hour, depending on the relative concentrations of the reagents.Some years ago, Turcsanyi proposed (Acta Chim., Acad.Scient.Hungar., 110 (1982) 305, Chem.Abs. 97 188877w) that a R-N=O/R-NH-OH system might exhibit oscillatory behaviour and the data presented are an experimental realization of that prediction.A mechanistic rationale is proposed to account for the observations.
- Li, Lijuan,Eaton, Donald R.,McGlinchey, Michael J.
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- INFLUENCE OF MOLECULAR STRUCTURE AND MOLECULAR ORDERING TYPE ON NITROXIDE FORMATION KINETICS IN SOME LOW TEMPERATURE SOLID STATES OF CYANOBIPHENYLS
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The influence of solid specimens' formation conditions on test photoinduced reactions of nitroxide generation has been studied in mesogenic cyanobiphenyls: 7OCB, 8OCB, 5CB, 8CB.Reaction kinetics appears to be a very sensitive instrument for investigation of the changes in local ordering and molecular dynamics which accompany solid structure formation before and during the course of reaction itself.
- Batyuk, V. A.,Shabatina, T. I.,Morosov, Yu. N.,Sergeev, G. B.
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- THE PHASE-STRUCTURAL TRANSITIONS IN LIQUID CRYSTALLINE ALKOXYCYANOBIPHENYLS AND THE KINETICS OF NITROXIDES FORMATION
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The kinetics of photoinduced nitroxides formation has been studied by ESR in mesogenic alkoxycyanobiphenyls 6OCB, 7OCB, 8OCB and their mixtures in temperature range 173-383 K.The nitroxide formation effectively takes place in isotropic, nematic, smectic and solid states of the systems.The reaction kinetics is sensitive to the phase structure on the molecular level.
- Shabatina, T. I.,Morosov, Yu. N.,Batyuk, V. A.,Sergeev, G. B.
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p. 277 - 281
(2007/10/02)
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- An electron spin resonance spin trapping investigation of azide oxidation on TiO2 powder suspensions
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The oxidation of azide has been studied on TiO2 powder suspensions in water, methanol, and mixtures of the two solvents.The esr spin trapping technique has been employed to provide evidence for the formation of azidyl radicals N.3.The results show that an aqueous alkaline medium is necessary to obtain a high production of N.3 radicals.A mechanism is proposed whereby the oxidation of N-3 is mainly due to reaction with OH. radicals which are in turn generated upon capture of holes by OH- groups adsorbed on TiO2.Azidyl anions adsorb weakly on TiO2 and do not displace adsorbed OH- from the surface.
- Maldotti, Andrea,Amadelli, Rossano,Carassiti, Vittorio
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- NITROXIDE FORMATION IN THE SOLID STATE OF THE LIQUID CRYSTAL 4-PENTYL-4'-CYANOBIPHENYL
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The formation of nitroxide during photolysis of 2-methyl-2-nitropropane in nematic liquid crystal 4-pentyl-2-nitrosopropane in nematic liquid crystal 4-pentyl-4'-(5CB) has been studied by ESR at temperatures 183-343K.The kinetics of nitroxide formation is sensitive to the phase state of liquid crystalline systems.In the solid state of 5CB the kinetic manifestation of hysteresis phenomena has been established.In nematic phase 5CB the equalization of rate constants for the tert-butyl radical trapping by nitrosocompounds of different chemical structures has been observed.
- Batyuk, V. A.,Shabatina, T. I.,Morosov, Yu. N.,Sergeev, G. B.
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p. 109 - 118
(2007/10/02)
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- On the Mechanism of Denitration of Aliphatic Nitro Compounds by Trialkylstannyl Radicals. An ESR and Kinetic Study
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Alkyl(trialkylstannyloxy) nitroxyl radicals 3 have been detected by ESR spectroscopy as intermediates in the denitration reaction of aliphatic nitro compounds with trialkylstannyl radicals (R' = Me, n-Bu), generated photolytically from hexa-n-alkylditins or tri-n-butyltin hydride in benzene solution.In most cases, the additional formation of dialkyl nitroxyl radicals 4 could be observed at prolonged reaction times.The decay kinetics of radicals 3 have been investigated by time-resolved ESR spectroscopy in the temperature range of 248 to 326 K.Alkyl(trialkylstannyloxy) nitroxyl radicals generated from tertiary nitro compounds decay by a first-order process, whereas those from secondary and primary nitro compounds follow broken reaction orders 1 A mechanistic scheme for the reaction of aliphatic nitro compounds with trialkylstannyl radicals is proposed, substantiated by a product study.
- Korth, Hans-Gert,Sustmann, Reiner,Dupuis, Jacques,Giese, Bernd
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p. 1197 - 1202
(2007/10/02)
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- Reactions of Ozonate and Superoxide Radical Anions
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Potassium ozonate has been prepared by reaction of ozone with potassium superoxide dispersed in Freon-12.Orange solutions of potassium ozonate in benzene or toluene containing 18-crown-6 react with nitrone traps to give spin adducts mainly derived from the oxide radical anion, which is a decomposition product of the ozonate radical anion.With 2-methyl-2-nitrosopropane in toluene solution the ozonate gives five nitroxide radicals in whose formation the oxide radical anion is again implicated.With nitrosobenzene electron transfer occurs.Comparable reactions with superoxide are described.
- Forrester, Alexander R.,Purushotham, Vemishetti
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p. 211 - 218
(2007/10/02)
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- Aminyl Oxides (Nitroxides), XXXVII. Formation of Vinylaminyl Oxides Substituted by Electron-Acceptor Groups and Related Radicals as Studied by ESR Spectroscopy
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Vinylaminyl oxides substituted by electron-acceptor groups at β-position have been prepared by various methods.Oxidation of nitrones 6 or the tautomeric N-vinylhydroxylamines 7 yields radicals 8a, b, z, and ae. 8 oe and ue arise from oxidation of the isoxazolines generated in situ from the isoxazolium salts 12.The bisvinylaminyl oxides 16 and 17 are prepared by oxidation of the corresponding N,N-bisvinylhydroxylamines.Oxidation of N,N-disubstituted hydroxylamines 10 or 14 affords initially aminyl oxides 11 or 15 which are further dehydrogenated to the vinylaminyl oxides 8a, l, m, o - t, x, y, and 2a - c, respectively. - With the exception of 8a and b vinylaminyl oxides could be detected only if there is a second substituent as a phenyl group, a second electron-acceptor group or a methylthio-, phenylthio-, or phenylseleno group at the β-position.Monosubstituted vinylaminyl oxides undergo a spin-trap reaction with their precursor nitrone to give spin adduct 19 or 20.
- Aurich, Hans Guenter,Schmidt, Michael,Schwerzel, Thomas
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p. 1086 - 1104
(2007/10/02)
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- On the Use of Glyoxal Bis(t-Butyl Nitrone) as a Spin Trap
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Nitroxides derived from glyoxal bis(t-butyl nitrone), GBBN, have been studied by e.s.r. spectroscopy.Well resolved e.s.r. spectra exhibiting extra hyperfine splitting by magnetic active nuclei in γ-position have been recorded for the spin adducts of alkyl, as well as .N3 and .CH2Cl radicals.Enhanced stability was found for the spin adducts of halogen atoms.However, a wider application of this spin trap is limited by the strong superposition of the e.s.r. signals of different radical spin adducts which is directly related to almost identical conformations of these nitroxides.
- Rehorek, Detlef,Janzen, Edward G.
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p. 968 - 982
(2007/10/02)
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- DARSTELLUNG UND THERMOLYSE VON HEXAKIS(PERFLUORORGANYLTHIO/SELENO)ETHANEN
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Thiocarbonylcompounds such as 1a, 1b, 1c, 1d, 1e and 1f were prepared and irradiated with UV-light in hexane solution.The products obtained in this photolyses are 3a, 3b and 3c.Only 3c dissociates in the temperature range 140-190 deg C reversible to 2c.The others, 3a and 3b, decompose yielding bis(trifluoromethyl)diselenide, 6b and 6d, without forming the corresponding methyl radical 2a and 2b.This was proved by spin-trapping experiments utilizing phenyl-t-butylnitrone.Attempts to prepare 3e were unsuccessful but led to the new compounds 7a, 7b, 7c, 1,1,1-tris(trifluoromethylseleno)ethan (7d) and, surprisingly, 9.Physical and spectroscopic data of the newly prepared substances are provided.
- Haas, Alois,Kempf, Karl W.
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p. 4963 - 4972
(2007/10/02)
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- N-NITRENES. I. FORMATION OF FREE RADICALS IN THE DISSOCIATION OF DIBENZYLAMINONITRENE
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By ESR with spin traps it was shown that the dissociation of dibenzylaminonitrene to nitrogen and bibenzyl takes place through the formation of benzyl radicals.Various methods of generation of dibenzylaminonitrene in the presence of spin traps (2-methyl-2-nitrosopropane, nitrosodurene, phenyl-N-tert-butyl-nitrone) give spin adducts (nitroxyl radicals) stable at room temperature.The formation of two nitroxyl radicals during the dissociation of dibenzylaminonitrene labeled at one methylene group with deuterium imdicates that one molecule of dibenzylaminonitrene gives two benzyl radicals during dissociation.
- Savin, V. I.,Morozov, V. I.,Kitaev, Yu. P.
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p. 866 - 870
(2007/10/02)
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- SPIN-TRAPPING OF α-AZIDOALKYL RADICALS
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Spin-trapping with 2-methyl-2-nitrosopropane of the α-azidoalkyl radicals derived from isopropyl and benzyl azides competes effectively with loss of nitrogen from these radicals at 313 K.
- Cook, Malcolm D.,Ng, Lee Len,Roberts, Brian P.
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p. 3761 - 3764
(2007/10/02)
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- Spin-trapping with 2-methyl-2-nitrosopropane: photochemistry of carbonyl-containing compounds. Methyl radical formation from dimethyl sulfoxide
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The photochemical reactions of several carbonyl-containing compounds investigated by spin-trapping with 2-methyl-2-nitrosopropane revealed different modes of scission depending on the structure of the initial compound.Thus, in photo-Fries rearrangements, the acyl radical was detected. 1,3-diphenyl-2-propanone decarbonylated to yield the benzyl radical.Finally, valerophenone yielded the radicals expected by γ-hydrogen abstraction.In a dark reaction, dimethyl sulfoxide reacts with NaOH to generate methyl radicals.The latter result suggests the need for caution in the use of dimethyl sulfoxide with 2-methyl-2-nitrosopropane for the detection of hydroxyl radicals.
- Rosenthal, Ionel,Mossoba, Magdi M.,Riesz, Peter
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p. 1486 - 1492
(2007/10/02)
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- A Spin Trap Investigation of Azolyl Radicals
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An ability of azolyl-anions to behave as one-electrons reductans in reactions with t-nitrosobutane and iron carbonyls are found in solutions.The azolyl radicals formed in reaction of azolyl-anions and azoles with t-BuNO have been trapped as corresponding nitroxide radicals.The formation of radicals from azoles can be described as consequence of proton and electron transfer acts. - Keywords: Spin Trap Investigation, Azolyl Radicals
- Babin, V. N.,Gumenyuk, V. V.,Solodovnikov, S. P.,Belousov, Yu. A.
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p. 400 - 401
(2007/10/02)
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- Studies on Spin-Trapped Radicals in γ-Irradiated Aqeuous Solutions of 2-Methyl-2-nitrosopropane by High-Performance Liquid Chromatography and ESR Spectroscopy
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Spin adducts produced in γ-irradiated aqueous solutions of 2-methyl-2-nitrosopropane were investigated by means of high-performance liquid chromatography and ESR spectroscopy.Five kinds of spin adducts were found and four of their structures identified as follows: t-BuN(O.)CH2C(CH3)2N(O-)N=O, t-BuN(O.)CH3, t-BuN(O.)CH2C(CH3)2N=O or t-BuN(O.)CH2C(CH3)2N+(O-)=N+(O-)-t-Bu, and t-BuN(O.)-t-Bu.
- Makino, Keisuke
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p. 1012 - 1015
(2007/10/02)
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- AMINYLOXIDE (NITROXIDE)-XXXI. UNTERSUCHUNG DER SPINDICHTEVERTEILUNG IN VERSCHIEDENEN AMINYLOXID-TYPEN MIT HILFE 17O-MARKIERTER RADIKALE
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17O-Labelled aminyloxides 4 and 7 have been prepared either by direct reaction of the intermediate aminyl radicals 3 and 6 generated by various methods, with 17O-enriched oxygen, or by spin trap reactions performed with 17O-labelled 2-methyl-2-nitrosopropane (8) and 2-methyl-2-nitropropane (13) respectively.Reaction of 17O-labelled tert-butylhydroxylamine with phoagen yielded 11 which was transformed to the radicals 4d and 4f.Using equations (3) and (4) the spin density pNNO and pONO was derived for some dialkylaminyloxides (for instance 4c X=CF3) and tert-butylaminyloxides with conjugated groups (4 X=CO-R, COCl, COOR, COONR2, CN).The spin density distribution in these radicals is discussed.An attempt to calculate the spin density in radicals 4 (X=OR, NR2 and SR) with aid of (3) and (4) yields too large values.For this reason we suggest that the aminyloxide group is non-planar in these radicals.
- Aurich, H. G.,Czepluch, H.
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p. 3543 - 3550
(2007/10/02)
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