7175-54-4Relevant academic research and scientific papers
Hydrogen abstraction from neurotransmitters by active oxygen species facilitated by intramolecular hydrogen bonding in the radical intermediates
Ohkubo, Kei,Moro-Oka, Yoshihiko,Fukuzumi, Shunichi
, p. 999 - 1001 (2006)
The reactivity of neurotransmitters toward hydrogen abstraction by an active oxygen species (the cumylperoxyl radical) is comparable to that of a strong antioxidant such as catechin due to the strong intramolecular hydrogen bonding, which has been successfully detected by ESR. The Royal Society of Chemistry 2006.
Mechanistic insights into the oxidation of substituted phenols via hydrogen atom abstraction by a cupric-superoxo complex
Lee, Jung Yoon,Peterson, Ryan L.,Ohkubo, Kei,Garcia-Bosch, Isaac,Himes, Richard A.,Woertink, Julia,Moore, Cathy D.,Solomon, Edward I.,Fukuzumi, Shunichi,Karlin, Kenneth D.
, p. 9925 - 9937 (2014/08/05)
To obtain mechanistic insights into the inherent reactivity patterns for copper(I)-O2 adducts, a new cupric-superoxo complex [(DMM-tmpa)CuII(O2?-)]+ (2) [DMM-tmpa = tris((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)amine] has been synthesized and studied in phenol oxidation-oxygenation reactions. Compound 2 is characterized by UV-vis, resonance Raman, and EPR spectroscopies. Its reactions with a series of para-substituted 2,6-di-tert-butylphenols (p-X-DTBPs) afford 2,6-di-tert-butyl-1,4-benzoquinone (DTBQ) in up to 50% yields. Significant deuterium kinetic isotope effects and a positive correlation of second-order rate constants (k2) compared to rate constants for p-X-DTBPs plus cumylperoxyl radical reactions indicate a mechanism that involves rate-limiting hydrogen atom transfer (HAT). A weak correlation of (kBT/e) ln k 2 versus Eox of p-X-DTBP indicates that the HAT reactions proceed via a partial transfer of charge rather than a complete transfer of charge in the electron transfer/proton transfer pathway. Product analyses, 18O-labeling experiments, and separate reactivity employing the 2,4,6-tri-tert-butylphenoxyl radical provide further mechanistic insights. After initial HAT, a second molar equiv of 2 couples to the phenoxyl radical initially formed, giving a CuII-OO-(ArO') intermediate, which proceeds in the case of p-OR-DTBP substrates via a two-electron oxidation reaction involving hydrolysis steps which liberate H2O2 and the corresponding alcohol. By contrast, four-electron oxygenation (O-O cleavage) mainly occurs for p-R-DTBP which gives 18O-labeled DTBQ and elimination of the R group.
Reactions of Mn(II) and Mn(III) with alkyl, peroxyalkyl, and peroxyacyl radicals in water and acetic acid
Jee, Joo-Eun,Bakac, Andreja
experimental part, p. 2136 - 2141 (2010/07/05)
The kinetics of oxidation of Mn(II) with acylperoxyl and alkylperoxyl radicals were determined by laser flash photolysis utilizing a macrocyclic nickel complex as a kinetic probe. Radicals were generated photochemically from the appropriate ketones in the presence of molecular oxygen. In both acidic aqueous solutions and in 95% acetic acid, Mn(II) reacts with acylperoxyl radicals with k = (0.5-1.6) × 106 M-1 s-1 and somewhat more slowly with alkylperoxyl radicals, k = (0.5-5) x 10 5 M-1 s-1. Mn(III) rapidly oxidizes benzyl radicals, k = 2.3 × 108 M-1 s-1 (glacial acetic acid) and 3.7 × 108 M-1 s-1 (95% acetic acid). The value in 3.0 M aqueous perchloric acid is much smaller, 1× 107 M-1 s-1. The decarbonylation of benzoyl radicals in H2O has k = 1.2 × 106 s -1.
Aliphatic C-H bond activation initiated by a (μ-η2: η2-peroxo)dicopper(II) complex in comparison with cumylperoxyl radical
Matsumoto, Takahiro,Ohkubo, Kei,Honda, Kaoru,Yazawa, Akiko,Furutachi, Hideki,Fujinami, Shuhei,Fukuzumi, Shunichi,Suzuki, Masatatsu
experimental part, p. 9258 - 9267 (2009/12/06)
A (μ-η2:η2-peroxo)dicopper(II) complex, [Cu2(H-L)(O2)]2+ (1-O2), supported by the dinucleating ligand 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl] benzene (H-L) is capable of initiating C-H bond activation of a variety of external aliphatic substrates (SHn): 10-methyl-9,10-dihydroacridine (AcrH2), 1,4-cyclohexadiene (1,4-CHD), 9,10-dihydroanthracene (9,10-DHA), fluorene, tetralin, toluene, and tetrahydrofuran (THF), which have C-H bond dissociation energies (BDEs) ranging from ～75 kcal mol-1 for 1,4-CHD to ～92 kcal mol-1 for THF. Oxidation of SH n afforded a variety of oxidation products, such as dehydrogenation products (SH(n-2)), hydroxylated and further-oxidized products (SH(n-1)OH and SH(n-2)=O), dimers formed by coupling between substrates (H(n-1)S-SH(n-1)) and between substrate and H-L (H-L-SH(n-1)). Kinetic studies of the oxidation of the substrates initiated by 1-O2 in acetone at -70°C revealed that there is a linear correlation between the logarithms of the rate constants for oxidation of the C-H bonds of the substrates and their BDEs, except for THF. The combination of this correlation and the relatively large deuterium kinetic isotope effects (KIEs), k2H/k2D (13 for 9,10-DHA, ?29 for toluene, and ～34 for THF at -70°C and ～9 for AcrH2 at -94°C) indicates that H-atom transfer (HAT) from SHn (SDn) is the rate-determining step. Kinetic studies of the oxidation of SHn by cumylperoxyl radical showed a correlation similar to that observed for 1-O2, indicating that the reactivity of 1-O2 is similar to that of cumylperoxyl radical. Thus, 1-O 2 is capable of initiating a wide range of oxidation reactions, including oxidation of aliphatic C-H bonds having BDEs from ～75 to ～92 kcal mol-1, hydroxylation of the m-xylyl linker of H-L, and epoxidation of styrene (Matsumoto, T.; et al. J. Am. Chem. Soc. 2006, 128, 3874).
Dynamics of the reactions of [meso-tetrakis(2,6-dimethyl-3-sulfonatophenyl)porphinato]-manganese(III) hydrate with various alkyl hydroperoxides in aqueous solution. Product studies and comparison of kinetic parameters
Arasasingham, Ramesh D.,Jeon, Seungwon,Bruice, Thomas C.
, p. 2536 - 2544 (2007/10/02)
The second-order rate constants (kly) for reactions of [meso-tetrakis(2,6-dimethyl-3-sulfonatophenyl)porphinato]manganese(III) hydrate [(1)MnIII(X)2, X = H2O or HO-] with t-BuOOH and (Ph)(Me)2COOH have been determined in aqueous solution in the pH range 7.3-12.6. The pH dependencies of kly were fitted to a kinetic expression (eq 2) that was similar to that shown previously to describe the pH dependence of the reaction of (1)MnIII(X)2 with (Ph)2(MeOCO)COOH. Comparison of the very similar pH-rate profiles for t-BuOOH, (Ph)(Me)2COOH, and (Ph)2(MeOCO)COOH (ROOH) showed that the log of the second-order rate constants exhibits only a modest dependency on the acidity of the ROH leaving group (-0.32 for the pH 7.3-10.0 range) as would be expected of a homolytic reaction. Product analysis on the reactions with t-BuOOH in the absence of the ABTS trapping agent provided (Me)2CO (60-70%) as the major product with the remainder of the oxidant recovered as t-BuOH (12%), t-BuOOMe, (t-BuO)2, MeOH, and HCHO. The product distributions showed no significant dependence on the pH of the reaction solutions. In the presence of ABTS (Me)2CO is formed in 5% yield, and the main product is t-BuOH (89%). These findings are consistent with a mechanism involving the homolytic (but not heterolytic) cleavage of the O-O bond of manganese(III)-coordinated alkyl hydroperoxide. Addition of imidazole to the reaction of (1)MnIII(X)2 with t-BuOOH resulted in a ～4-10-fold enhancement in the rate of reaction. The pH dependence of log klm for the reaction in the presence of imidazole, from pH 5.3 to 12.6, was found to be in accord with that determined previously for (Ph)2- (MeOCO)COOH. The product distribution for the reactions in the presence of imidazole showed significant dependence on the pH of the reaction mixtures. At pH 7.8 and 10.0 the product profiles were only consistent with a homolytic mechanism for the O-O bond cleavage where the major product was (Me)2CO (63-67%), with the remainder being t-BuOH (19%), t-BuOOMe (13-16%), (t-BuO)2, MeOH, and HCHO. At pH 12.6, the yield of t-BuOH (63%) increased dramatically with concomitant decreases in the yields of (Me)2CO (34%), t-BuOOMe (4%), (t-BuO)2, MeOH, and HCHO. The latter product distribution finds explanation in a change in mechanism of the O-O bond cleavage from homolysis to heterolysis as a result of the proton dissociation of the manganese(III)-coordinated ImH (i.e., (1)MnIII(OOR)(ImH) → [(1)MnIII(OOR)(Im)]-). The acidity dependences of the 1e- oxidation and reduction potentials of (1)MnIII(X)(ImH) have been used to determine the acid ionization constants for the mono-imidazole-ligated (1)MnII(H2O)(ImH), (1)MnIII(H2O)(ImH), and (1)MnIII(H2O)(ImH) species. The change in 1e- oxidation potentials with pH has also been compared to the change in rate constants with pH for reactions occurring in the presence and absence of imidazole.
Structure and Reactivity of Peroxyl and Sulphoxyl Radicals from Measurement of Oxygen-17 Hyperfine Couplings: Relationship with Taft Substituent Parameters
Sevilla, Michael D.,Becker, David,Yan, Mengyao
, p. 3279 - 3286 (2007/10/02)
A series of peroxyl radicals (ROO.) with substituent groups of varying electron withdrawing power have been investigated using electron paramagnetic resonance spectroscopy.Sixteen carbon-based radicals have been produced, identified and reacted with 17O-l
