79579-90-1

Upstream product

• 950-99-2 2,2,5,7,8-pentamethylchroman-6-ol 
• 16812-36-5 cumyloxyl radical 
• 1310558-97-4 3-benzotriazin-4-one-N-oxyl radical 
• 1310558-96-3 3-quinazolin-4-one-N-oxyl radical 
• 1169875-50-6 C₇H₆N₃O 
• 1169875-48-2 6-trifluoromethyl-1H-1,2,3-benzotriazol-N-oxyl 
• 50349-73-0 benzotriazole N-oxyl radical 

Downstream Products

• 950-99-2 2,2,5,7,8-pentamethylchroman-6-ol 

Relevant academic research and scientific papers

Effects of metal ions distinguishing between one-step hydrogen- and electron-transfer mechanisms for the radical-scavenging reaction of (+)-catechin

A kinetic study of a hydrogen-transfer reaction from (+)-catechin (1) to galvinoxyl radical (G·) has been performed using UV-vis spectroscopy in the presence of Mg(ClO4)2 in deaerated acetonitrile (MeCN). The rate constants of hydrogen transfer from 1 to (G·) determined from the decay of the absorbance at 428 nm due to (G·) increase significantly with an increase in the concentration of Mg2+. The kinetics of hydrogen transfer from 1 to cumylperoxyl radical has also been examined in propionitrile (EtCN) at low temperature with use of ESR. The decay rate of cumylperoxyl radical in the presence of 1 was also accelerated by the presence of scandium triflate [Sc(OTf)3 (OTf = OSO2CF3)]. These results indicate that the hydrogen-transfer reaction of (+)-catechin proceeds via electron transfer from 1 to oxyl radicals followed by proton transfer rather than via a one-step hydrogen atom transfer. The coordination of metal ions to the one-electron reduced anions may stabilize the product, resulting in the acceleration of electron transfer.

Kinetic Studies of Antioxidant Activity of New Tocopherol Model Compounds in Solution

The second-order rate constants ks for the reaction of 10 kinds of tocopherol (vitamin E) model compounds with stable phenoxyl radical in ethanol have been measured at 25.0 deg C, using a stopped-flow spectrophotometer, as a model reaction of tocopherols with unstable free radicals ROO., RO., and HO.) in biological systems.The absolute ks values of α-, β-, γ-, and δ-tocopherol models are similar to or slightly smaller than those of the corresponding tocopherols having a long-phytyl-chain.The relative ks values (α:β:γ:δ = 100:53:50:24), that is, relative antioxidant activities, of α-, β-, γ-, and δ-tocopherol models are in good agreement with those (100:44:47:20) of α-, β-, γ-, and δ-tocopherols.The antioxidant activities of tocopherol models having two alkyl substituents, such as methyl, ethyl, isorpopyl, and t-butyl groups, at ortho positions of OH group are similar to each other, suggesting that the effect of steric hindrance on the reaction rate is small. 5,7-Dimethyltocol model has quite similar rate constants with those of β- and γ-tocopherol models, whereas γ-tocopherol model is only ca. 24percent as reactive as α-tocopherol model and tocol model is only ca. 10percent as reactive as α-tocopherol model.The result indicates that the rate constants increase as the total electron donating capacity of the alkyl substituents at aromatic ring increases.For the tocopherol models log ks was found to correlate with Σ?+ substituent constants with a ρ+ value of -1.0.

Effects of magnesium ion on kinetic stability and spin distribution of phenoxyl radical derived from a vitamin E analogue: Mechanistic insight into antioxidative hydrogen-transfer reaction of vitamin E

The phenoxyl radical 1. of a vitamin E analogue, generated by the reaction of 2,2,5,7,8-pentamethylchroman-6-ol (1H) with 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH.) or galvinoxyl (G.), was significantly stabilized by the presence of Mg2+. Addition of Mg2+ into a solution of 1. resulted in a red shift of the absorption band of 1. as well as a decrease in the g value of the EPR spectrum of 1., indicating a complex formation between 1. and Mg2+. The complexation between the phenoxyl radical and Mg2+ significantly retards the disproportionation reaction of 1. by electronic repulsion between the metal cation and a generated organic cation (1+), leading to stabilization of the organic radical species. No effect of Mg2+ on the rate of hydrogen atom transfer from 1H to DPPH. or to G. was observed, suggesting that the hydrogen-transfer reaction between 1H and DPPH. or G. proceeds via a one-step hydrogen atom transfer mechanism rather than electron-transfer followed by proton transfer.

Hydroperoxyl Radicals (HOO.): Vitamin E Regeneration and H-Bond Effects on the Hydrogen Atom Transfer

Hydroperoxyl (HOO.) and alkylperoxyl (ROO.) radicals show a different behavior in H-atom-transfer processes. Both radicals react with an analogue of α-tocopherol (TOH), but HOO., unlike ROO., is able to regenerate TOH by a fast H-atom transfer: TO.+HOO.→TOH+O2. The kinetic solvent effect on the H-atom transfer from TOH to HOO.is much stronger than that observed for ROO.because noncovalent interactions with polar solvents (Solv???HOO.) destabilize the transition state.

Importance of π-stacking interactions in the hydrogen atom transfer reactions from activated phenols to short-lived N-oxyl radicals

A kinetic study of the hydrogen atom transfer from activated phenols (2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols, 2,2,5,7,8- pentamethylchroman-6-ol, caffeic acid, and (+)-cathechin) to a series of N-oxyl radical (4-substituted phthalimide-N-oxyl radicals (4-X-PINO), 6-substituted benzotriazole-N-oxyl radicals (6-Y-BTNO), 3-quinazolin-4-one-N-oxyl radical (QONO), and 3-benzotriazin-4-one-N-oxyl radical (BONO)), was carried out by laser flash photolysis in CH3CN. A significant effect of the N-oxyl radical structure on the hydrogen transfer rate constants (kH) was observed with kH values that monotonically increase with increasing NO-H bond dissociation energy (BDENO-H) of the N-hydroxylamines. The analysis of the kinetic data coupled to the results of theoretical calculations indicates that these reactions proceed by a hydrogen atom transfer (HAT) mechanism where the N-oxyl radical and the phenolic aromatic rings adopt a π-stacked arrangement. Theoretical calculations also showed pronounced structural effects of the N-oxyl radicals on the charge transfer occurring in the π-stacked conformation. Comparison of the kH values measured in this study with those previously reported for hydrogen atom transfer to the cumylperoxyl radical indicates that 6-CH3-BTNO is the best N-oxyl radical to be used as a model for evaluating the radical scavenging ability of phenolic antioxidants.

Phenol-based lipophilic fluorescent antioxidant indicators: A rational approach

(Chemical Equation Presented) The reactivity, electrochemistry, and photophysics of the novel antioxidant indicator B-TOH, a BODIPY-α- tocopherol adduct, were investigated. We also studied a newly prepared BODIPY-3,5-di-tert-butyl-4-hydroxybenzoic acid ad

Unexpected acid catalysis in reactions of peroxyl radicals with phenols**

Weak organic acids in millimolar concentrations increase the reactivity of peroxyl radicals with common phenolic antioxidants dramatically. This counterintuitive phenomenon relies on a substantially different reaction mechanism from that in the absence of an acid: rate-determining electron transfer occurs from the hydrogen-bonded phenol to the hydroperoxide cation radical present in equilibrium with the peroxyl radical under these conditions (see scheme).

Vitamin E chemistry. studies into initial oxidation intermediates of α-tocopherol: Disproving the involvement of 5a-C-centered "chromanol methide" radicals

(Chemical Equation Presented) Contrary to concepts handed down in the literature from the early days of vitamin E research, one-electron oxidation of vitamin E does not involve 5a-C-centered radicals. A combined approach of analytical techniques, in particular electron paramagnetic resonance spectroscopy (EPR), organic synthesis of special derivatives, isotopic labeling, kinetic studies, and computational chemistry was used to re-evaluate the one-electron and two-electron oxidation chemistry of α-tocopherol (α-toc). EPR in combination with 5a-13C-labeled compounds provided no indication of the involvement of 5a-C-centered radicals. Oxidation of special tocopherol derivatives were used to disprove the occurrence of 5a-C-centered one-electron intermediates. Additionally it was shown that those vitamin E reactions that were commonly evoked to plead for the involvement of C-centered tocopheryl radicals actually proceeded via heterolytic, i.e., non-radical, intermediates. The results will help to clear widely spread misunderstandings about the chemistry of vitamin E and will have mechanistic implications for the synthesis of tocopherol-based supramolecular structures and 5a-substituted α-tocopherol derivatives.

Antioxidant properties of natural and synthetic chromanol derivatives: Study by fast kinetics and electron spin resonance spectroscopy

(Chemical Equation Presented) Chromanol-type compounds act as antioxidants in biological systems by reduction of oxygen-centered radicals. Their efficiency is determined by the reaction rate constants for the primary antioxidative reaction as well as for disproportionation and recycling reactions of the antioxidant-derived radicals. We studied the reaction kinetics of three novel chromanols: cis- and trans-oxachromanol and the dimeric twin-chromanol, as well as ubichromanol and ubichromenol, in comparison to α-tocopherol and pentamethylchromanol. The antioxidant-derived radicals were identified by optical and electron spin resonance spectroscopy (ESR). The kinetics of the primary antioxidative reaction and the disproportionation of the chromanoxyl radicals were assessed by stopped-flow photometry in different organic solvents to simulate the different polarities associated with biomembranes. Furthermore, the reduction of the chromanoxyl radicals by ubiquinol and ascorbate was measured after laser-induced one-electron chromanol oxidation in ethanol and in a micellar system, respectively. The rate constants showed that twin-chromanol had better radical scavenging properties than α-tocopherol and a significantly slower disproportionation rate of its corresponding chromanoxyl radical. In addition, the radical derived from twin-chromanol is reduced by ubiquinol and ascorbate at a faster rate than the tocopheroxyl radical. Finally, twin-chromanol can deliver twice as many reducing equivalents, which makes this compound a promising new candidate as artificial antioxidant in biological systems.

Reactivity of substituted phenols toward alkyl radicals

The rate constants for the reaction of primary alkyl radicals with substituted phenolic compounds have been measured in benzene or toluene at room temperature by using the radical clock technique. With three representative phenols, containing in the ortho positions substituents of different size, the kinetics of the hydrogen transfer to alkyl radicals was studied at different temperatures to obtain the corresponding Arrhenius parameters. The kinetic solvent effect on the reaction with α-tocopherol was also investigated in six different solvents behaving as hydrogen bond acceptors, while the reaction with 2,4,6-trimethylphenol and 2,6-di-tert-butylphenol was studied in toluene and γ-valerolactone. For some phenols, the effect of self-aggregation on the kinetic parameters was also studied.