Kinetics and mechanism of aniline hydroxylation by cumene hydroperoxide in the presence of catalase

In a phosphate buffer with pH=7.4 at 20°C the kinetics of aniline hydroxylation to p-aminophenol by the catalase-cumene hydroperoxide system has been studied. The reaction mechanism of this system is discussed.

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20°C pH 7,4 - . .

     

Aerobic oxidation of cumene to cumene hydroperoxide catalyzed by metalloporphyrins

A protocol for the aerobic oxidation of cumene to cumene hydroperoxide (CHP) catalyzed by metalloporphyrins is reported herein. Typically, the reaction was performed in an intermittent mode under an atmospheric pressure of air and below 130°C. Several important reaction parameters, such as the structure and concentration of metalloporphyrin, the air flow rate, and the temperature, were carefully studied. Analysis of the data obtained showed that the reaction was remarkably improved by the addition of metalloporphyrins, in terms of both the yield and formation rate of CHP while high selectivity was maintained. It was discovered that 4 or 5 h was the optimal reaction time when the reaction was catalyzed by monomanganese-porphyrin ((p-Cl)TPPMnCl) (7.20 × 10^?5 mol/l) at 120°C with the air flow rate being 600 ml/min. From the results, we also found that higher concentration of (p-Cl)TPPMnCl, longer reaction time and higher reaction temperature were all detrimental to the production of CHP from cumene. Studies of the reaction kinetics revealed that the activation energy of the reaction (E) is around 38.9 × 10⁴ kJ mol^?1. The low apparent activation energy of the reaction could explain why the rate of cumene oxidation to CHP in the presence of metalloporphyrins was much faster than that of the non-catalyzed oxidation.     

Kinetics and mechanism of nucleophilic substitution of dichloroarylazopyridinepalladium(II) by pyridine bases

The reaction of dichloroarylazopyridinepalladium(II) [Pd(aap)Cl2, aap=4-RC6H4N-N-2-C5H4N; R= H (1), Me (2), Cl (3)] with pyridine bases [RPy: R-H (a), 2-Me(b), 4-Me(c), 4-Cl(d), 2-Ph(e), 2-PhCH2(f)] has been studied spectrophotometrically in MeCN at 400nm. The products (4) have been isolated and characterized as trans-Pd(RPy)2Cl2. The kinetics of the nucleophilic substitution have been examined under pseudo-first-order conditions with respect to base at 298K and follow the rate law, Rate=k[RPy]2 [Pd(aap)Cl2]. The rate data supports a nucleophilic association path. External addition of Cl– (LiCl) suppresses the rate, which follows the order: k(3)> k(1)>k(2), where k values are linearly related to Hammet constants. 2-Substitution in the pyridine base remarkably reduces the rate compared with 4-substitution and is attributed to a steric effect that destabilizes the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (e)>(f)>(b). The 4-substituted pyridines control the rate via the inductive effect and follow the order: (d)>(a)>(c).     

Kinetics and mechanism of oxidation oftrans-1,2-diaminocyclohexanetetraacetatocobaltate(II) by periodate

Summary The kinetics of oxidation oftrans-1,2-diaminocyclohexanetetraacetatocobaltate(II), Co^IICDTA^2–, by periodate were studied using either excess periodate or excess complex concentrations. When periodate was in excess the reaction showed first-order dependence on [IO ₄ ^– ] and first-order and second-order dependences on [Co^IICDTA^2–]. First-order dependence in each reactant was obtained when the complex was in excess. The reaction rate was found to be independent of pH over the range 4–5, but increasing with increasing ionic strength. The enthalpy and the entropy of activation were calculated using the transition state theory equation.     

Kinetics and mechanism of oxidation of the drug mephenesin by bis(hydrogenperiodato)argentate(III) complex anion

Mephenesin is being used as a central‐acting skeletal muscle relaxant. Oxidation of mephenesin by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO₆)₂]^5?, has been studied in aqueous alkaline medium. The major oxidation product of mephenesin has been identified as 3‐(2‐methylphenoxy)‐2‐ketone‐1‐propanol by mass spectrometry. An overall second‐order kinetics has been observed with first order in [Ag(III)] and [mephenesin]. The effects of [OH^?] and periodate concentration on the observed second‐order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced: k′ = (k_a + k_b[OH^?])K₁/{f([OH^?])[IO^?₄]_tot + K₁}, where [IO^?₄]_tot denotes the total concentration of periodate, k_a = (1.35 ± 0.14) × 10^?2M^?1s^?1 and k_b = 1.06 ± 0.01 M^?2s^?1 at 25.0°C, and ionic strength 0.30 M. Activation parameters associated with k_a and k_b have been calculated. A mechanism has been proposed to involve two pre‐equilibria, leading to formation of a periodato‐Ag(III)‐mephenesin complex. In the subsequent rate‐determining steps, this complex undergoes inner‐sphere electron transfer from the coordinated drug to the metal center by two paths: one path is independent of OH^? whereas the other is facilitated by a hydroxide ion. In the appendix, detailed discussion on the structure of the Ag(III) complex, reactive species, as well as pre‐equilibrium regarding the oxidant is provided. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 440–446, 2007     

Thermal hazard investigation of cumene hydroperoxide in the first oxidation tower

This article studies the thermokinetics and safety parameters of cumene hydroperoxide (CHP) manufactured in the first oxidation tower. Vent sizing package 2 (VSP2), an adiabatic calorimeter, was employed to determine reaction kinetics, the exothermic onset temperature (T ₀), reaction order (n), ignition runaway temperature (T _{C, I}), etc. The n value and activation energy (E _a) of 15?mass% CHP were calculated to be 0.5 and 120.2?kJ?mol^?1, respectively. The heat generation rate (Q _g) of 15?mass% CHP compared with hS (cooling rate)?=?6.7?J?min^?1?K^?1 of heat balance, the T _S,E and the critical extinction temperature (T _{C, E}) under 110?°C of ambient temperature (T _a) were calculated 111 and 207?°C, respectively. The Q _g of 15?mass% CHP compared with hS?=?0.3?J?min^?1?K^?1 of heat balance was applied to determine the T _{C, I} that was evaluated to be 116?°C. This article describes the best operating conditions when handling CHP, starting from the first oxidation tower.     

Kinetics and mechanism of the Co(II)-assisted oxidation of thioureas by dioxygen

Catalytic oxidation of N,N'-dimethylthiourea and thiourea by dioxygen in water using a new cobalt(II) complex of octasulfophenyltetrapyrazinoporphyrazine was performed under mild conditions. The reaction is shown to include the formation of an intermediate anionic five-coordinate complex followed by an unusual two-electron oxidation to produce the corresponding urea and elemental sulfur (S8). Kinetic and thermodynamic parameters for the different reaction steps of the process were determined. Drastic differences in catalytic activity of cobalt and iron octasulfophenyltetrapyrazinoporphyrazines were observed.     

Cu(II)氧化抗坏血酸的动力学和机理

本文在总离子强度I=1.00mol.dm^-^3、[Cu^2^+]>>[H2A]、[H^+]>>[H2A]、无氧及无缓冲剂存在的条件下, 研究Cu(II)氧化抗坏血酸(H2A)的动力学和机理. 发现Cu(II)与H2A不发生配位反应, 但以Cl^-存在的情况下, 确有Cu(II)的H2A配合物生成, Cu(II)氧化H2A反应的速率方程为r={a+b[Cl^-]}[Cu^2^+]{[H+]+Ka}^-^2, 25℃时a和b值分别为4.08×10^-^4s^-^1和0.555dm^3.s^-^1.mol^-^1. Cu(II)氧化H2A反应的表观活化能为68.1KJ.mol^-^1. 根据动力学结果, 提出了反应机理, 并给出了配合物ClCuHA的结构形式.     

Mechanistic studies of the sensitized photoreduction of bis(acetylacetonato)copper(II) by phenylalkyl ketones

Bis(acetylacetonato)copper(II) (Cu(acac)₂) interacts with both the triplet excited state and the triplet biradical of phenylalkyl ketones which undergo the Norrish type II reaction. Mechanistic studies by static quenching methods show that the triplet biradicals interact with the paramagnetic copper species, leading to the preferential formation of cyclobutanols without the formation of new products; in the presence of Ph₃P the former interaction causes the known reduction of Cu(acac)₂) to Cu(acac)(Ph₃P)₂, with a rate constant of about 6 × 10⁹ M⁻¹ s⁻¹. It is shown that Ph₃P interacts with one reactive intermediate, the triplet excited state ketone. The results of extensive kinetic analysis strongly support the proposed reaction mechanism.     

Palladium-catalyzed carbonylative cross-coupling of organoboranes with aryl iodides or benzyl halides in the presence of bis(acetylacetonato)zinc(II)

Carbonylative cross-coupling reactions of organoboranes with aryl iodides and benzyl halides successfully catalyzed by dichlorobis(triphenylphosphine)palladium(II) in the presence of bis(acetylacetonato)zinc(II) produce unsymmetrical ketones in reasonable yields.     

Application of zone-melting technique to metal chelate systems-X Zone-refining of bis(acetylacetonato)beryllium(II), tris(acetylacetonato)aluminium(III) and bis(di-isovalerylmethanato)copper(II)

Bis(acetylacetonato)beryllium(II), tris(acetylacetonato)aluminium(III) and bis(di-isovaleryl-methanato)copper(II) were zone-refined. Also crude beryllium(II), aluminium(III) and copper(II) salts were purified by zone-melting the above-mentioned chelates, obtained by precipitation from aqueous methanol solutions. Some contaminants were excluded at the stage of chelate formation and the remainder were concentrated at the terminal end of a zone-refining column.     

Synthesis and structure of (pyridine) bis(acetylacetonato) (1-methyl-1-phenylethylperoxo) cobalt (III)

Synthesis and structure of (pyridine) bis(acetylacetonato) (1-methyl-1-phenylethylperoxo) cobalt(III) complex are described.

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() () (III).

     

Decomposition of cumene hydroperoxide in the presence of metal 1,2-dithiolate complexes

Metal 1,2-dithiolate complexes were studied as catalysts for decomposition of cumene hydroperoxide. Reaction proceeds by a two-stage process and the first stage, corresponding to destruction of the metal complex, is influenced by the type of metal and substituents on the dithiolate ligand. On average, almost two sulfur atoms in each metal chelate are oxidized to SO₂ or SO₃, which decompose the main part of hydroperoxide.

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1,2- . : . SO₂ SO₃, .

     

Kinetics and mechanism of the oxidation of a heterocyclic thioamide by silver(II)-cyclam

The kinetics of the oxidation of 4,6-dimethyl-2-mercaptopyrimidine (DMP) by Ag(cyclam)²⁺ were studied in buffer solutions from pH 5.8 to 7.2 at constant ionic strength of 0.10?M?(NaClO₄). The reaction is observed to be first-order with respect to [Ag(cyclam)²⁺] and to [DMP]. However, the reaction rate is affected by the pH of the solution owing to the acid–base equilibrium of the thiol. The mechanism postulated to account for the kinetics includes an acid–base equilibrium and oxidation of thiol (RSH) and thiolate ion (RS^?) by Ag(cyclam)²⁺ to RS^· radicals which undergo rapid dimerization to form disulfide (RSSR). From the postulated mechanism and the observed kinetics a rate expression was derived, and second-order rate constants and activation parameters were calculated. The pK _a values of the acid dissociation reaction of DMP were also determined at four temperatures using spectrophotometric methods, and thermodynamic parameters calculated from the K _a values.