2143-58-0Relevant articles and documents
Temperature-Dependent Rate Constants and Product Branching Ratios for the Gas-Phase Reaction Between CH3O2 and ClO
Helleis, Frank,Crowley, John N.,Moortgat, Geert K.
, p. 11464 - 11473 (1993)
Kinetic and product branching data have been measured for the reaction of CH3O2 radicals with ClO in the temperature range 225-355 K using the discharge-flow/mass spectrometry technique.The pressure-independent overall reaction rate constant is described by k(12)(225-355 K) = (3.25 +/- 0.50) * 10-12 exp((-114 +/- 38)/T) cm3 molecule-1 s-1.Two reaction channels were identified, leading to CH3O + ClOO (12a) and CH3OCl + O2 (12b), respectively.The branching ratios, α12a = k12a/k12 and α12b = k12b/k12, are also independent of pressure and are described by α12a = (1.51 +/- 0.56) exp((-218 +/- 93)/T) and α12b = (0.080 +/- 0.059) exp((-377 +/- 178)/T).These expressions yield roughly equal rate constants of k12a and k12b of ca. 1 * 10-12 cm3 molecule-1 s-1 at the low temperatures prevalent in the polar winter and early springtime stratosphere.We thus identify CH3OCl as a potentially important species in ozone hole chemistry.
Electron-transfer reactions of alkyl peroxy radicals
Jovanovic, Slobodan V.,Jankovic, Ivana,Josimovic, Ljubica
, p. 9018 - 9021 (2007/10/02)
One-electron-transfer reactions of alkyl peroxy radicals were studied by pulse radiolysis of aqueous solutions. At pH 13, the methyl peroxy radical was found to rapidly, k = 1 × 105-4.9 × 107 s-1, and quantitatively oxidize various organic substrates with E13 = 0.13-0.76 V vs NHE. On the other hand, this radical was unreactive with compounds with E13 ≥ 0.85 V. Consequently, E13 of the methyl peroxy radical is higher than 0.76 V and lower than 0.85 V, which means that E7 is in the range 1.02-1.11 V. At pH 8, the rate constants of the oxidation of four ferrocene derivatives by the alkyl peroxy radicals ranged from 7.1 × 104 M-1 s-1 for ferrocenedicarboxylate (E8 = 0.66 V) to 2.3 × 106 M-1 s-1 for (hydroxymethyl)ferrocene (E8 = 0.42 V). These rate constants were used to evaluate the reduction potential and self-exchange rate of alkyl peroxy radicals in neutral media from the Marcus equation. The calculated E7 = 1.05 V is in excellent agreement with the estimated E7 = 1.02-1.11 V and with one of the perviously published values E7 = 1.0 V, but the value is in excellent agreement higher than the other E7 ～ 0.6 V. It is suggested that the high reorganization energy, λ = 72 kcal mol-1 redox couple originates from the requirement for solvent reorganization due to the solvation of hydroperoxide anion in the transition state. In support of this are the activation parameters of the reaction of the methyl peroxy radical with uric acid. The activation entropy is 9 eu lower at pH 7.3 than it is at pH 13.2, whereas the activation enthalpies are unchanged. The importance of entropy control was verified in the reactions of cyclohexyl peroxy radicals with α- and δ-tocopherol in aerated cyclohexane (ΔH+ ≈ 0 kcal/mol, and ΔS+ = -25 and -26 eu). The implications of these findings on the inactivation of alkyl peroxy radicals in general are discussed.
Reactivities of Acylperoxy Radicals in the Photoreaction of α-Diketones and Oxygen
Sawaki, Yasuhiko,Ogata, Yoshiro
, p. 3344 - 3349 (2007/10/02)
The photoepoxidation of olefins with α-diketones and oxygen has been studied mechanistically focusing on the reactivities of intermediate radicals.One mole of α-diketone resulted in the formation of 2 mol of epoxide together with 2 equiv of C-C cleavage of olefins.The photoepoxidation proceeds via acylperoxy radicals RCO3* and the C-C cleavage of olefins is caused by acyloxy radical RCO2*.The addition of RCO3* to olefins was found to be ca.105-fold faster than that of acylperoxy radical ROO*.The relative reactivities of olefins suggest that acylperoxy radicals behave as a strongly electrophilic radical.That is, ρ values of -1 (vs.?+) obtained in the photoepoxidation of substituted styrenes are of the same magnitude as those in the epoxidation with molecular peracids.Although the relative reactivities of olefins toward the photoepoxidation roughly parallel those for the peracid epoxidations, the additivity of methyl substituent is not always operative.This is explained by a steric retardation by too many substituents on the carbon attacked by RCO3* in addition to the relative stabilities of resulting adduct radicals between olefins and RCO3*.Since acylperoxy radicals are not reactive towards sulfides, sulfoxides, or pyridine, a selective epoxidation of double bonds is possible.The relative reactivities of olefins toward benzoyloxy and methylperoxy redicals revealed a much less electrophilic nature of these oxy radicals, the ρ values for styrenes being -0.1 to -0.2.
