Mechanism of RuIV-catalyzed oxidation of alkanes in aqueous solutions

Rudakov, E. S.; Tret'yakov, V. P.; Min'ko, L. A.; Tishchenko, N. A.

doi:10.1007/bf02077033

Cited by 16 publications

(26 citation statements)

References 3 publications

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“…The order of the reaction in the Fenton system relative to the substrate found relative to the rate of its consumption, may vary from first (for [RH] from 10 -7 to 10 -5 M) to zero (for [RH] > 10 -4 M), which is related to the dependence of the steady-state concentration of hydroxyl radicals on [RH] [13,14]. Under the conditions studied ([RH] £ 10 -5 M) over the entire temperature range from 5 to 55°C, the rate of consumption of the hydrocarbons was first-order relative to each of the substrates:…”

Section: Resultsmentioning

confidence: 99%

“…The previously observed anomalously low substrate selectivity for the reactions of alkanes with OH radicals in aqueous solution in comparison with the gas-phase reactions was explained quantitatively [13,14] by hindered diffusion in the framework of the cage effect model. When this effect is operative, the KIE and selectivity of the reactions in solution are lower than in the gas phase due to competition between C-H bond breaking reactions in the collision complex in the solvent cage RH OH K ⋅ and the diffusional decomposition of this complex.…”

Section: Temperature Dependence Of Kie and C-c 6 H 12 /C-c 5 H 10 Ratmentioning

confidence: 96%

“…In previous work [13,14], we carried out a systematic study of the kinetics and selectivity of the reactions of OH radicals with a wide range of normal, iso, and cycloalkanes in the oxidative system containing H 2 O 2 , Fe 2+ , Fe 3+ , and water similar to Fenton's reagent [3]. We found unusually low substrate selectivity and hydrogen kinetic isotope effect (KIE) for reaction (1) in aqueous solution in comparison with the gas-phase reactions.…”

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Kinetics and anomalous temperature dependence of the kinetic isotope effect of reactions of cycloalkanes C5H10, C6H12 and C6D12 with OH radicals in aqueous solutions

et al. 2008

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in aqueous solution and in the gas phase has opposite signs. Values for the KIE and k 6 /k 5 decrease with increasing temperature from 5 to 55°C in the gas phase, while these values increase in solution. We propose that this phenomenon is a consequence of a solvent cage effect.The reactions of hydroxyl radicals with hydrocarbons play an important role in biochemical processes and the chemistry of the atmosphere and natural water supplies [1][2][3][4]. The kinetics of the reactions of OH radicals with saturated hydrocarbons (RH)including cycloalkanes, has been studied extensively in the gas phase [1]. The absolute rate constants for reaction (1) have been measured in aqueous solution only for methane [5,6], while relative rate constants in the methane series have been measured for butane [7-10] and cyclopentane [11,12].In previous work [13,14], we carried out a systematic study of the kinetics and selectivity of the reactions of OH radicals with a wide range of normal, iso, and cycloalkanes in the oxidative system containing H 2 O 2 , Fe 2+ , Fe 3+ , and water similar to Fenton's reagent [3]. We found unusually low substrate selectivity and hydrogen kinetic isotope effect (KIE) for reaction (1) in aqueous solution in comparison with the gas-phase reactions. These findings were qualitatively explained by diffusion complications for the reactions in solution related to the cage effect [13].A new approach toward the study of the mechanisms for activation of C-H bonds of saturated hydrocarbons by oxidizing agents, metal complexes, and electrophiles developed in previous work [13,15] involves study of the temperature dependence of the KIE for cyclohexane/cyclohexane-d 6 pairs and the ratios of the reaction rates for the cyclopentane/cyclohexane pair and analysis of the compensation ratios obtained. There have been no data on the temperature dependence of the rate constants of the reactions of alkanes with OH radicals in aqueous solution.

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Section: Resultsmentioning

confidence: 99%

Section: Temperature Dependence Of Kie and C-c 6 H 12 /C-c 5 H 10 Ratmentioning

confidence: 96%

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confidence: 99%

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Kinetics and anomalous temperature dependence of the kinetic isotope effect of reactions of cycloalkanes C5H10, C6H12 and C6D12 with OH radicals in aqueous solutions

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“…The KIE values for the attack on the C--H bond by the three species are close, as in the case of alkanes3, 38,50 k_CH/k_ cD = koCH/ko cO = k+CH/k+ cB. (16) 2.…”

Section: Rudakov and Lobachevmentioning

confidence: 85%

The first step of oxidation of alkylbenzenes by permanganates in acidic aqueous solutions

Rudakov

Lobachev

2000

Russ Chem Bull

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Data on the kinetics, kinetic isotope effects, substrate selectivity, and activation parameters for the first step of oxidation of alkylbenzenes by permanganate in acidic aqueous solutions are surveyed. The MnO4-. HMnO.~. and lVlnO3" species serve as oxidants at different acidities. The increase in the positive charge in this series enhances the electrophilicity of the reagent, which manifests itself as an increase in the reaction rate and a change in the site of attack on the atkylbenzene molecule (either the aromatic ring or C-H bond in the alkyl group). The oxidation of the alkyl C--H bonds in alkylbenzenes and in alkanes follows similar mechanisms, while the attack on the aromatic ring proceeds via the electrophilic aromatic substitution mechanism with a transition state intermediate between the charge transfer complex and r

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“…The absolute rate constants have been measured only for methane by a method involving g-radiolysis of aqueous solutions [5, 6], while relative constants for the methane-butane series [7-9] and for cyclopentane [10] were measured by photolysis and radiolysis methods. There have been no data given for the temperature dependence of the rate constants.In previous work [11,12], we studied the kinetics and selectivity of reaction (1) in H 2 O 2 -Fe 2+ -Fe 3+ -H 2 O solutions at 25°C for broad range of normal, iso-, and cycloalkanes. We used a direct and most precise method for studying the activation kinetics of hydrocarbons based on measurement of the rate of consumption of trace amounts of RH under conditions of a large excess of the oxidizing agent [12].…”

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Temperature dependence of the relative rate constants of the reactions of alkanes with oh radicals in aqueous solution

2009

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The values of k RH /k EtH decrease with increasing temperature in the gas phase but increase in water. The behavior of these reactions in water may be attributed to a solvent cage effect.The reactions of hydrocarbons with hydroxyl radicals ( ⋅ OH) hold importance in the chemistry of the atmosphere and natural water sources [1,2]. OH Radicals are key oxidants of hydrocarbons (RH) in the troposphere as well as in surface, rainwater and cloud water [1,3], and in the ozonization of water [4]. The kinetics of the reactions (1) RH + ⋅ OH ® [R…H…OH] ¹ ® R ⋅ + H 2 O and the temperature dependence of the rate constants for a broad range of alkanes have been studied extensively in the gas phase [1]. Considering the marked discrepancies in the values of the rate constants and activation parameters given by different workers, we shall subsequently use the values recommended by Atkinson [1]. Reactions (1) in aqueous solution have not been studied as extensively. The absolute rate constants have been measured only for methane by a method involving g-radiolysis of aqueous solutions [5, 6], while relative constants for the methane-butane series [7-9] and for cyclopentane [10] were measured by photolysis and radiolysis methods. There have been no data given for the temperature dependence of the rate constants.In previous work [11,12], we studied the kinetics and selectivity of reaction (1) in H 2 O 2 -Fe 2+ -Fe 3+ -H 2 O solutions at 25°C for broad range of normal, iso-, and cycloalkanes. We used a direct and most precise method for studying the activation kinetics of hydrocarbons based on measurement of the rate of consumption of trace amounts of RH under conditions of a large excess of the oxidizing agent [12]. The anomalously low substrate selectivity and kinetic isotope effect (KIE) for reaction (1) in aqueous solution in comparison with the gas phase were quantitatively attributed to the cage effect on diffusion [11,12]. Important additional information on mechanism can be obtained by studying the temperature dependence of the rate constant and substrate selectivity (rate constant ratios) for a broad range of hydrocarbons [13]. In recent work [14], we have shown that the temperature dependence of the KIE in gas-phase and liquid-phase reactions of cyclohexane (c-C 6 H 12 /C 6 D 12 ) with the OH radical at 5-55°C have opposite signs: the KIE values in the gas phase drop with increasing temperature, while these values increase in water. These discrepancies are presumably a consequence of the solvent cage effect. 0040-5760/09/4504-0239

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Mechanism of RuIV-catalyzed oxidation of alkanes in aqueous solutions

Cited by 16 publications

References 3 publications

Kinetics and anomalous temperature dependence of the kinetic isotope effect of reactions of cycloalkanes C5H10, C6H12 and C6D12 with OH radicals in aqueous solutions

Kinetics and anomalous temperature dependence of the kinetic isotope effect of reactions of cycloalkanes C5H10, C6H12 and C6D12 with OH radicals in aqueous solutions

The first step of oxidation of alkylbenzenes by permanganates in acidic aqueous solutions

Temperature dependence of the relative rate constants of the reactions of alkanes with oh radicals in aqueous solution

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