C:Corrosive;126517-51-9Relevant articles and documents
Kinetics and thermodynamics of reversible disproportionation-comproportionation in redox triad oxoammonium cations - Nitroxyl radicals - Hydroxylamines
Sen, Vasily D.,Tikhonov, Ivan V.,Borodin, Leonid I.,Pliss, Evgeny M.,Golubev, Valery A.,Syroeshkin, Mikhail A.,Rusakov, Alexander I.
, p. 17 - 24 (2015)
Kinetics and equilibrium of the acid-catalyzed disproportionation of cyclic nitroxyl radicals R2NO· to oxoammonium cations R2NO+ and hydroxylamines R2NOH is defined by redox and acid-base properties of these compounds. In a recent work (J. Phys. Org. Chem. 2014, 27, 114-120), we showed that the kinetic stability of R2NO· in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R2NO+ and R2NOH to R2NO· and found that increasing in -I-effects of substituents greatly reduces the overall equilibrium constant of the reaction K4. This occurs because of both the increase of acidity constants of hydroxyammonium cations K3H+ and the difference between the reduction potentials of oxoammonium cations ER2NO+/R2NO· and nitroxyl radicals ER2NO·/R2NOH. pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E1/3σ and bond dissociation energies D(O-H) for hydroxylamines R2NOH inwater were determined. For a wide variety of piperidine- and pyrrolidine-1-oxyls values of pK3H+ and ER2NO+/R2NO· correlate with each other, as well aswith the equilibriumconstants K4 and the inductive substituent constants ωI. The correlations obtained allowprediction of the acid-base and redox characteristics of redox triads R2NO·-R2NO+-R2NOH.
KINETICS AND MECHANISM OF THE WO42--CATALYZED OXIDATION OF DI-tert-ALKYLAMINES AND DI-tert-ALKYLHYDROXYLAMINES TO NITROXYL RADICALS BY HYDROGEN PEROXIDE
Sen', V. D.,Golubev, V. A.,Efremova, N. N.
, p. 53 - 63 (1982)
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Effect of structural modification on photodynamic activity of hypocrellins
Ma, Jianghua,Zhao, Jingquan,Jiang, Lijin
, p. 143 - 148 (2001)
Aluminum ion complexed 5,8-di-Br-hypocrellin B is a new water-soluble perylenequinonoid derivative with enhanced absorption over hypocrellin B (HB) in the phototherapeutic window (600-900 nm). Electron paramagnetic resonance and 9,10-diphenyl-anthracene bleaching methods were used to investigate the photosensitizing activity of [Al2(5,8-di-Br-HB)Cl4]n in the presence of oxygen. Singlet oxygen, superoxide anion radical and hydroxyl radical can be generated by [Al2(5,8-di-Br-HB)Cl4]n photosensitization. Singlet oxygen (1O2) is formed via energy transfer from triplet-state [Al2(5,8-diBr-HB)Cl4]n to ground-state molecular oxygen. 1O2 participates in the generation of a portion of superoxide anion radical (02.-). Besides superoxide anion radical (O2.-) may originate from the electron transfer between the triplet-state [Al2(5,8-di-Br-HB)Cl4]n and the ground-state molecular oxygen. OH is formed through the Fenton-Haber-Weiss reaction and the decomposition of DMPO-1O2 adduct. Compared with HB [Al2(5,8-di-Br-HB)Cl4]n primarily remains and enhances the generation efficiency of superoxide anion radical and hydroxyl radical but that of singlet oxygen decreases.
Suemmermann,Deffner
, p. 593,594,595 (1975)
Quantitation of Li2O2 stored in Li-O2 batteries based on its reaction with an oxoammonium salt
Hase, Yoko,Ito, Emi,Shiga, Tohru,Mizuno, Fuminori,Nishikoori, Hidetaka,Iba, Hideki,Takechi, Kensuke
, p. 8389 - 8391 (2013)
Precise knowledge of the discharge and charge reactions within Li-O 2 batteries is an important aspect of developing highly efficient, rechargeable Li-O2 cells. We describe an analytical method capable of determining the quantity of
TEMPO-Mediated Catalysis of the Sterically Hindered Hydrogen Atom Transfer Reaction between (C5Ph5)Cr(CO)3H and a Trityl Radical
Gunasekara, Thilina,Abramo, Graham P.,Hansen, Andreas,Neugebauer, Hagen,Bursch, Markus,Grimme, Stefan,Norton, Jack R.
, p. 1882 - 1886 (2019)
We have demonstrated the ability of TEMPO to catalyze H· transfer from (C5Ph5)Cr(CO)3H to a trityl radical (tris(p-tert-butylphenyl)methyl radical). We have measured the rate constant and activation parameters for the direct reaction, and for each step in the catalytic process: H· transfer from (C5Ph5)Cr(CO)3H to TEMPO and H· transfer from TEMPO-H to the trityl radical. We have compared the measured rate constants with the differences in bond strength, and with the changes in the Global Electrophilicity Index determined with high accuracy for each radical using state of the art quantum chemical methods. We conclude that neither is a major factor in determining the rates of these H· transfer reactions and that the effectiveness of TEMPO as a catalyst is largely the result of its relative lack of steric congestion compared to the trityl radical.
Unveiling chemical reactivity and structural transformation of two-dimensional layered nanocrystals
Han, Jae Hyo,Lee, Sujeong,Yoo, Dongwon,Lee, Jae-Hyun,Jeong, Sohee,Kim, Jin-Gyu,Cheon, Jinwoo
, p. 3736 - 3739 (2013)
Two-dimensional (2D) layered nanostructures are emerging fast due to their exceptional materials properties. While the importance of physical approaches (e.g., guest intercalation and exfoliation) of 2D layered nanomaterials has been recognized, an understanding of basic chemical reactions of these materials, especially in nanoscale regime, is obscure. Here, we show how chemical stimuli can influence the fate of reaction pathways of 2D layered nanocrystals. Depending on the chemical characteristics (Lewis acid (1O 2) or base (H2O)) of external stimuli, TiS2 nanocrystal is respectively transformed to either a TiO2 nanodisc through a "compositional metathesis" or a TiO2 toroid through multistage "edge-selective structural transformation" processes. These chemical reactions can serve as the new design concept for functional 2D layered nanostructures. For example, TiS2(disc)- TiO2(shell) nanocrystal constitutes a high performance type II heterojunction which not only a wide range solar energy coverage (～80%) with near-infrared absorption edge, but also possesses enhanced electron transfer property.
Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation
Warren, Jeffrey J.,Mayer, James M.
, p. 5282 - 5287 (2010)
Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO ?) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold's model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments areshown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethylpiperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions.
DUAL REACTIVITY OF 1,2-DISUBSTITUTED DIHYDRO-N-HETEROAROMATIC SYSTEMS. 2. MECHANISM OF THE DEHYDROGENATION OF N-ACYLDIHYDROQUINOLINES AND ISOQUINOLINES WITH 2,2,6,6-TETRAMETHYL-1-OXOPIPERIDINIUM PERCHLORATE
Skorobogatova, Z. M.,Golubev, V. A.,Sheinkman, A. K.
, p. 63 - 69 (1981)
The mechanism of the heterocyclic dehydrogenation of various N-acyl derivatives of α-substituted 1,2-dihydroquinolines and isoquinolines with 2,2,6,6-tetramethyl-1-oxopiperidinium perchlorate was investigated.
Saturation kinetics in phenolic O-H bond oxidation by a mononuclear Mn(III)-OH complex derived from dioxygen
Wijeratne, Gayan B.,Corzine, Briana,Day, Victor W.,Jackson, Timothy A.
, p. 7622 - 7634 (2014)
The mononuclear hydroxomanganese(III) complex, [MnIII(OH)(dpaq)] +, which is supported by the amide-containing N5 ligand dpaq (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate) was generated by treatment of the manganese(II) species, [MnII(dpaq)] (OTf), with dioxygen in acetonitrile solution at 25 °C. This oxygenation reaction proceeds with essentially quantitative yield (greater than 98% isolated yield) and represents a rare example of an O2-mediated oxidation of a manganese(II) complex to generate a single product. The X-ray diffraction structure of [MnIII(OH)(dpaq)]+ reveals a short Mn-OH distance of 1.806(13) A, with the hydroxo moiety trans to the amide function of the dpaq ligand. No shielding of the hydroxo group is observed in the solid-state structure. Nonetheless, [MnIII(OH)(dpaq)]+ is remarkably stable, decreasing in concentration by only 10% when stored in MeCN at 25 °C for 1 week. The [MnIII(OH)(dpaq)]+ complex participates in proton-coupled electron transfer reactions with substrates with relatively weak O-H and C-H bonds. For example, [Mn III(OH)(dpaq)]+ oxidizes TEMPOH (TEMPOH = 2,2′-6,6′-tetramethylpiperidine-1-ol), which has a bond dissociation free energy (BDFE) of 66.5 kcal/mol, in MeCN at 25 °C. The hydrogen/deuterium kinetic isotope effect of 1.8 observed for this reaction implies a concerted proton-electron transfer pathway. The [Mn III(OH)(dpaq)]+ complex also oxidizes xanthene (C-H BDFE of 73.3 kcal/mol in dimethylsulfoxide) and phenols, such as 2,4,6-tri-t- butylphenol, with BDFEs of less than 79 kcal/mol. Saturation kinetics were observed for phenol oxidation, implying an initial equilibrium prior to the rate-determining step. On the basis of a collective body of evidence, the equilibrium step is attributed to the formation of a hydrogen-bonding complex between [MnIII(OH)(dpaq)]+ and the phenol substrates.
Hydrogen atom transfer reactions of a ruthenium imidazole complex: Hydrogen tunneling and the applicability of the marcus cross relation
Wu, Adam,Mayer, James M.
, p. 14745 - 14754 (2008)
The reaction of RuII(acac)2(py-imH) (Ru IIimH) with TEMPO? (2,2,6,6-tetramethylpiperidine-1- oxyl radical) in MeCN quantitatively gives RuIII(acac) 2(py-im) (RuIIIim) and the hydroxylamine TEMPO-H by transfer of H? (H+ + e-) (acac = 2,4-pentanedionato, py-imH = 2-(2′-pyridyl)imidazole). Kinetic measurements of this reaction by UV-vis stopped-flow techniques indicate a bimolecular rate constant k3H = 1400 ± 100 M-1 s-1 at 298 K. The reaction proceeds via a concerted hydrogen atom transfer (HAT) mechanism, as shown by ruling out the stepwise pathways of initial proton or electron transfer due to their very unfavorable thermochemistry (ΔG°). Deuterium transfer from RuII(acac) 2(py-imD) (RuIIimD) to TEMPO? is surprisingly much slower at k3D = 60 ± 7 M-1 s -1, with k3H/k3D = 23 ± 3 at 298 K. Temperature-dependent measurements of this deuterium kinetic isotope effect (KIE) show a large difference between the apparent activation energies, E a3D - Ea3H = 1.9 ± 0.8 kcal mol-1. The large k3H/k3D and ΔEa values appear to be greater than the semiclassical limits and thus suggest a tunneling mechanism. The self-exchange HAT reaction between RuIIimH and Ru IIIim, measured by 1H NMR line broadening, occurs with k4H = (3.2 ± 0.3) × 105 M-1 s -1 at 298 K and k4H/k4D = 1.5 ± 0.2. Despite the small KIE, tunneling is suggested by the ratio of Arrhenius pre-exponential factors, log(A4H/A4D) = -0.5 ± 0.3. These data provide a test of the applicability of the Marcus cross relation for H and D transfers, over a range of temperatures, for a reaction that involves substantial tunneling. The cross relation calculates rate constants for Ru IIimH(D) + TEMPO? that are greater than those observed: k3H,calc/k3H = 31 ± 4 and k 3D,calc/k3D = 140 ± 20 at 298 K. In these rate constants and in the activation parameters, there is a better agreement with the Marcus cross relation for H than for D transfer, despite the greater prevalence of tunneling for H. The cross relation does not explicitly include tunneling, so close agreement should not be expected. In light of these results, the strengths and weaknesses of applying the cross relation to HAT reactions are discussed.
Coordination chemistry of stable radicals: Homolysis of a titanium-oxygen bond
Huang, Kuo-Wei,Waymouth, Robert M.
, p. 8200 - 8201 (2002)
Thermolysis of Cp2TiCl(TEMPO) (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl) at 60 °C in a benzene/CCl4 mixture generates Cp2TiCl2. Kinetic studies implicate a mechanism involving the reversible cleavage of a Ti-O bond to generate the TEMPO radical and Cp2TiCl, which is trapped by CCl4 to give Cp2TiCl2. The rate of this reaction is strongly inhibited by added TEMPO and increases with increasing CCl4 concentration, indicating that the coupling of TEMPO to Cp2TiCl is faster than chloride atom abstraction from CCl4. Copyright
Electrochemical oxidation of 1-chloro(bromo)-2,2,6,6-tetramethylpiperidines
Kagan,Yanilkin,Nastapova,Morozov,Zhukova,Kashparov,Kashparova
, p. 2151 - 2156 (2011)
Electrochemical oxidation of 1-haloamines of the 2,2,6,6- tetramethylpiperidine series results in the formation of relatively stable radical-cations, detected by the methods of cyclic voltammetry and ESR spectroscopy. The final products of electrochemical oxidation of these haloamines are stable nitroxyl radicals. Pleiades Publishing, Ltd., 2011.
Photosensitizing properties of the porphycene immobilized in sol-gel derived silica coating films
Shimakoshi, Hisashi,Baba, Tatsushi,Iseki, Yusuke,Endo, Ayataka,Adachi, Chihaya,Watanabe, Midori,Hisaeda, Yoshio
, p. 6198 - 6201 (2008)
Porphycene was covalently immobilized in a sol-gel silica film deposited on a glass plate, and the immobilized porphycene showed a photosensitizing property with recycling for the photo-oxidation of 1,5-dihydroxynaphthalene.
Establishing plasmon contribution to chemical reactions: alkoxyamines as a thermal probe
Guselnikova, Olga,Audran, Gérard,Joly, Jean-Patrick,Trelin, Andrii,Tretyakov, Evgeny V.,Svorcik, Vaclav,Lyutakov, Oleksiy,Marque, Sylvain R. A.,Postnikov, Pavel
, p. 4154 - 4161 (2021)
The nature of plasmon interaction with organic molecules is a subject of fierce discussion about thermal and non-thermal effects. Despite the abundance of physical methods for evaluating the plasmonic effects, chemical insight has not been reported yet. In this contribution, we propose a chemical insight into the plasmon effect on reaction kinetics using alkoxyamines as an organic probe through their homolysis, leading to the generation of nitroxide radicals. Alkoxyamines (TEMPO- and SG1-substituted) with well-studied homolysis behavior are covalently attached to spherical Au nanoparticles. We evaluate the kinetic parameters of homolysis of alkoxyamines attached on a plasmon-active surface under heating and irradiation at a wavelength of plasmon resonance. The estimation of kinetic parameters from experiments with different probes (Au-TEMPO,Au-SG1,Au-SG1-TEMPO) allows revealing the apparent differences associated with the non-thermal contribution of plasmon activation. Moreover, our findings underline the dependency of kinetic parameters on the structure of organic molecules, which highlights the necessity to consider the nature of organic transformations and molecular structure in plasmon catalysis.
Tuning of the thermochemical and kinetic properties of ascorbate by its local environment: Solution chemistry and biochemical implications
Warren, Jeffrey J.,Mayer, James M.
, p. 7784 - 7793 (2010)
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.
Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells
Yamada, Ayato,Abe, Manabu,Nishimura, Yoshinobu,Ishizaka, Shoji,Namba, Masashi,Nakashima, Taku,Shimoji, Kiyofumi,Hattori, Noboru
, p. 863 - 873 (2019)
Novel caged nitroxides (nitroxide donors) with near-infrared two-photon (TP) responsive character, 2,2,6,6-tetramethyl-1-(1-(2-(4-nitrophenyl)benzofuran-6-yl)ethoxy)piperidine (2a) and its regioisomer 2b, were designed and synthesized. The one-photon (OP) (365 ± 10 nm) and TP (710–760 nm) triggered release (i.e., uncaging) of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical under air atmosphere were discovered. The quantum yields for the release of the TEMPO radical were 2.5% (2a) and 0.8% (2b) in benzene at ≈1% conversion of 2, and 13.1% (2a) and 12.8% (2b) in DMSO at ≈1% conversion of 2. The TP uncaging efficiencies were determined to be 1.1 GM at 740 nm for 2a and 0.22 GM at 730 nm for 2b in benzene. The cytocidal effect of compound 2a on lung cancer cells under photolysis conditions was also assessed to test the efficacy as anticancer agents. In a medium containing 100 μg mL?1 of 2a exposed to light, the number of living cells decreased significantly compared to the unexposed counterparts (65.8% vs 85.5%).
Hydrogenation of Nitroxides on Pt/SiO2
Kawai, Tadashi,Jarjoui, Milad,Burwell, Robert L.
, p. 2951 - 2956 (1982)
The hydrogenation of the nitroxide 2,2,6,6-tetramethylpiperidinyl-N-oxy (TMPNO) in ethylcyclohexane and other solvents has been studied from 0.6 to 35 deg C on Pt/SiO2.Hydrogenations were sandwiched between hydrogenations of cyclopentene using the techniques of Hussey et al.Results were shown to be uninfluenced by mass transfer of hydrogen between gas and liquid phases and in the catalyst pores.Significant levels of poisons in the TMPNO appeared to have been absent.Rates of hydrogenation of TMPNO to the hydroxylamine were very fast.At 20 deg C, turnover frequencies per se cond per surface atom of Pt for the loss of unsaturated molecules were ca. 130 for TMPNO and ca. 13 for cyclopentene, and Ea's were 21 and 34 kJ mol-1, respectively.The rates were zero order in TMPNO and about first order in hydrogen.In competitive hydrogenations of equimolar mixtures, TMPNO hydrogenated 3 times faster than cyclopentene.It appears that both TMPNO and cyclopentene absorb strongly enough on Pt to form an essentially saturated adsorbed layer and that the rate of hydrogenation is that of the dissociative adsorption of hydrogen at gaps in the adsorbed layer of the unsaturated molecule.The relative rates of hydrogenation of such molecules are then proportional to the product (effective area of gaps)x(sticking coefficient of hydrogen).
Cacalol and cacalol acetate as photoproducers of singlet oxygen and as free radical scavengers, evaluated by EPR spectroscopy and TBARS
Gomez-Vidales, Virginia,Granados-Oliveros, Gilma,Nieto-Camacho, Antonio,Reyes-Solis, Mirna,Jimenez-Estrada, Manuel
, p. 1371 - 1377 (2014)
Photodynamic therapy (PDT) is an emerging cancer treatment based on the production of singlet oxygen (1O2) upon illumination of a photosensitizer in the presence of oxygen. Antioxidants are primarily reducing agents prone to scavenge reactive species in one way or another. Cacalol (C) and cacalol acetate (CA) were examined and compared regarding to their capacity to produce singlet oxygen and as scavengers of free radicals. Their role as singlet oxygen photoproducers under UV-vis light irradiation was examined by electron paramagnetic resonance (EPR) using 2,2,6,6-tetramethyl-piperidine (TEMP) as spin-trapping material. The quantum yield to produce 1O2 was found to be 0.4 ± 0.05 for CA and 0.13 ± 0.05 for C. Their properties as scavengers of hydroxyl (OH), nitrogen-centered (2,2-diphenyl-1-picryhydrazyl radical, DPPH) and organic radicals (R and ROO) were evaluated using EPR and the thiobarbituric reactive substances (TBARS) method. C and CA differed in their abilities to trap DPPH. By contrast, both compounds showed similar activity to trap OH, R and ROO. A relationship between the redox potentials of the compounds and their activity as scavengers of DPPH was observed. The producing/inhibiting properties showed by C and CA make them interesting options for new therapeutic applications to treat tumors and other diseases.
Rozantzev,Neiman
, p. 131,136 (1964)
TEMPO reacts with oxygen-centered radicals under acidic conditions
Amorati, Riccardo,Pedulli, Gian Franco,Pratt, Derek A.,Valgimigli, Luca
, p. 5139 - 5141 (2010)
In the presence of organic acids in organic media, 2,2,6,6- tetramethylpiperidine-N-oxyl (TEMPO) reacts with peroxyl radicals at nearly diffusion-controlled rates by proton-coupled electron transfer from the protonated nitroxide. The Royal Society of Chemistry 2010.
Copper/TEMPO Redox Redux: Analysis of PCET Oxidation of TEMPOH by Copper(II) and the Reaction of TEMPO with Copper(I)
Ryan, Michael C.,Whitmire, Lauren D.,McCann, Scott D.,Stahl, Shannon S.
, p. 10194 - 10200 (2019)
Copper salts and organic aminoxyls, such as TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl), are versatile catalysts for aerobic alcohol oxidation. Previous reports in the literature contain conflicting proposals concerning the redox interactions that take place between copper(I) and copper(II) salts with the aminoxyl and hydroxylamine species, TEMPO and TEMPOH, respectively. Here, we reinvestigate these reactions in an effort to resolve the conflicting claims in the literature. Under anaerobic conditions, CuIIX2 salts [X = acetate (OAc), trifluoroacetate (TFA), and triflate (OTf)] are shown to promote the rapid proton-coupled oxidation of TEMPOH to TEMPO: CuIIX2 + TEMPOH → CuIX + TEMPO + HX. In the reaction with acetate, however, slow reoxidation of CuIOAc occurs. This process requires both TEMPO and HOAc and coincides with the reduction of TEMPO to 2,2,6,6-tetramethylpiperidine. Analogous reactivity is not observed with trifluoroacetate and triflate species. Overall, the facility of the proton-coupled oxidation of TEMPOH by CuII salts suggests that this process could contribute to catalyst regeneration under aerobic oxidation conditions.
INFLUENCE OF CHEMICAL STRUCTURE OF NITROXYL SPIN LABELS ON THEIR REDUCTION BY ASCORBIC ACID
Couet, W. R.,Brasch, R. C.,Sosnovsky, G.,Lukszo, J.,Prakash, I.,et. al.
, p. 1165 - 1172 (1985)
The influence of structure on the reduction of nitroxyl spin labels by ascorbic acid was examined using both piperidine and pyrrolidine nitroxyls.A five-fold molar excess of ascorbic acid and pH of 7.4 were used.The nitroxyl concentration was measured by electron spin resonance spectrometry.The five-membered (pyrrolidine) nitroxyls were more stable than the six-membered derivatives.Ring substituents also influenced the reaction.The anionic derivatives were more stable than the unionized compounds which, in turn, were more stable than the amines (cations at pH 7.4).
The effect of viscosity on the coupling and hydrogen-abstraction reaction between transient and persistent radicals
Li, Xiaopei,Kato, Tatsuhisa,Nakamura, Yasuyuki,Yamago, Shigeru
supporting information, p. 966 - 972 (2021/04/29)
The effect of viscosity on the radical termination reaction between a transient radical and a persistent radical undergoing a coupling reaction (Coup) or hydrogen abstraction (Abst) was examined. In a non-viscous solvent, such as benzene (bulk viscosity bulk 99% Coup/Abst selectivity, but Coup/Abst decreased as the viscosity increased (89/11 in PEG400 at 25 °C [bulk = 84 mPa s]). While bulk viscosity is a good parameter to predict the Coup/Abst selectivity in each solvent, microviscosity is the more general parameter. Poly(methyl methacrylate) (PMMA)-end radicals had a more significant viscosity effect than polystyrene (PSt)-end radicals, and the Coup/Abst ratio of the former dropped to 50/50 in highly viscous media (bulk = 3980 mPa s), while the latter maintained high Coup/ Abst selectivity (84/16). These results, together with the low thermal stability of dormant PMMA-TEMPO species compared with that of PSt-TEMPO species, are attributed to the limitation of the nitroxide-mediated radical polymerization of MMA. While both organotellurium and bromine compounds were used as precursors of radicals, the former was superior to the latter for the clean generation of radical species.
Method for preparing hindered amine nitroxide free radical compound by alkaline heterogeneous catalysis system
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Paragraph 0050-0053; 0058-0059, (2021/09/26)
The method comprises the following steps: dissolving a hindered amine compound in an organic solvent; adjusting pH by a carbonate aqueous solution; reacting with an aqueous hydrogen peroxide solution; and generating a hindered amine nitroxide free radical compound (IV). (V) Or (VI). The method is high in universality, and the hindered amine nitroxide free radical compound with various structures is prepared. The method is high in catalytic activity, short in reaction time, high in yield, simple in preparation process and convenient to operate; a high-purity target product can be obtained through simple phase separation, drying and concentration in the post-treatment process; meanwhile, the aqueous solution system and ethyl acetate can be recycled. Small by-products.
