Kinetics of the liquid-phase oxidation of 2-hydroxycyclohexanone

The kinetics of oxygen uptake in the azobisisobutyronitrile-initiated oxidation of 2-hydroxycy-clohexanone (RCH(OH)C(O)R) at 323 K has been investigated (chlorobenzene solvent, [RCH(OH)C(O)R] = 0.15-1.30 mol/L, initiation rate of w _i = 0.016–0.473 mol L^?1 s^?1). The effective oxidizability parameter k _{p, eff}(2k _t,eff)^?0.5 has been determined by solving the inverse kinetic problem using the entire data array obtained while varying [RCH(OH)C(O)R] and w _i. The rate constants of chain propagation and termination and the equilibrium constant of the addition of the hydroxyperoxyl radical to the ketoalcohol have been derived from the dependence of the oxidizability parameter on the substrate concentration. The rate constant of bimolecular chain initiation has been calculated to be k ₀ = 9.7 × 10^?7 L mol^?1 s^?1. The ratio of the rate constants of quadratic-law peroxyl radical recombination reactions without and with chain termination (k _eff′/k _t,eff′) increases with increasing [RCH(OH)C(O)R], passes through a maximum at a substrate concentration of 0.8 mol/L, and then falls off. It is demonstrated that this effect is due to the variation of the proportions of the hydroperoxyl and organic (1-hydroxy-2-oxocyclohexylperoxyl or 1,2-dihydroxy-1-cyclo-hexylperoxyl) radicals in the reaction medium.     

Effect of imidazole on the structure and properties of Zn-5,15-di(o-methoxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetrabutylporphyrin in reaction with organic peroxides

The reaction of Zn-5,15-di(o-methoxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetrabutylporphyrin with organic peroxides in the presence of imidazole was studied in order to investigate the effect of modification and deformation of the macrocycle on the redox properties of metalloporphyrins. The kinetic characteristics of the reaction were obtained. It was found that the introduction of imidazole into the reaction mixture resulted in an increase in the rate of oxidation of zincporphyrin. Quantum-chemical calculations of the reagents and intermediates of the oxidation reaction were performed at the PM3 level of theory. The deformational distortions of the free macrocycle and during the course of the reaction were estimated. The effect of the structure modification and the degree of deformation of the macrocyclic ligand on the parameters of the process [effective (k _eff) and true (k _v) rate constants] was found.     

Rate constants for addition of phenoxyl radicals to the vinyl monomer double bond

Rate constants were measured for the addition of the 2,4,6-tri(tert-butyl)phenoxyl radical (logk ₁₀, [liter/(mole · sec)]) to the double bond of styrene (9.73 – 4621/T), methyl methacrylate (10.1 – 4972.7/T) and butylacrylate (7.68 – 4313.9/T); and for addition of the 2,4,6-tribromophenoxyl radical to styrene (k ₁₀=0.5;T=323 K). A simulation based on these constants for the inhibited oxidation of styrene under conditions similar to those of monomer storage demonstrated the need to take account of this reaction when analyzing kinetic schemes describing the inhibited oxidation process.Institute of Nonaqueous Solution Chemistry, Russian Academy of Sciences, 150003 Ivanovo. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2713–2718, December, 1992.     

DSC study of linolenic acid autoxidation inhibited by BHT,dehydrozingerone and olivetol

Non-isothermal oxidation of linolenic acid (LNA) in bulk phase was monitored by differential scanning calorimetry. The kinetic parameters E _a, Z and k (activation energies, pre-exponential factors, and rate constants, respectively) were calculated by Ozawa-Flynn-Wall method for the first detectable exothermic effect of uninhibited LNA oxidation. The kinetic parameters were also calculated for LNA oxidation inhibited by 2,6-di-tert-butyl-4-methylphenol (BHT), and two natural compounds, 1,3-dihydroxy-5-pentylbenzene (olivetol), and 4-(4’-hydroxy-3’-methoxyphenyl)-3-buten-2-one (DHZ, dehydrozingerone) at various concentrations. For oxidation processes at 25, 90 and 180°C the plots of logk values vs. concentration of phenolic compounds indicated that optimal concentration of inhibitor determined for one particular temperature cannot be extrapolated to other temperatures.     

Determination of the Kinetic Significance of Elementary Steps in the Reaction of Ethylbenzene Oxidation Inhibited by para-Substituted Phenols: Choice of an Effective Antioxidant

A conceivable method (value method) for analyzing the reaction kinetics models of inhibited liquid-phase oxidation of organic compounds was considered. A procedure for the numerical calculations of the molecular structure parameters of an inhibitor and an inhibitor concentration that results in a maximum inhibition of the reaction was presented. In the kinetic model of a chain reaction of liquid-phase ethylbenzene oxidation in the presence of a para-methylphenol inhibitor, the dynamics of contributions from individual steps was calculated. This allowed us to simplify the reaction mechanism. The inhibition of the oxidation reaction due to reactions with the participation of a phenoxyl radical was found to occur under conditions of the quasi-equilibriumRO ₂ ^· +HO'RRO₂H +OC₆H₄'RThe molecular structures and initial concentrations of para-substituted phenols, which are most effective for the given reaction conditions, were determined.     

Inhibited Oxidation of Cumene and Polymerization of Styrene Investigated by Solution Microcalorimetry

The application of solution microcalorimetry was demonstrated on two model examples – inhibited oxidation of cumene and radical polymerization of styrene.From the experimental dependences of the rate of heat release on time, the rate constants k ₇ of the interaction of an inhibitor with radicals of substrate (RO ₂ ^. or R^.) in oxidation or in polymerization were determined for the set of inhibitors of N-aryl N-(2-quinone) amine series. It was shown that these compounds are weak inhibitors of oxidation of cumene and rather efficient inhibitor of polymerization of styrene.This revised version was published online in November 2005 with corrections to the Cover Date.     

Decomposition of cyclic acetone peroxides in acid media

The kinetics and stoichiometry of the formation of active oxygen (AO) in the acidic decomposition of trimeric (TATP) and dimeric (DADP) cyclic acetone peroxides are considered. Fe(III) produced as a result of Fe(II) oxidation with active oxygen has been determined using rhodanide procedure. The kinetics of the formation of active oxygen is described by a first order equation. The effective rate constant of TATP decomposition depends on the Hammett acidity function H ₀: log k _eff = ?H ₀ ? 2.6 (k _eff is in s^?1). Consequently, the decomposition rate of TATP is limited by protonation. In the HCl and H₂SO₄ concentration range from 0.006 to 2.9 mol/L, the decomposition of DADP occurs with k _eff = 0.0010 ± 0003 s^?1 at a Fe(II) concentration of 3.5 mmol/L and k _eff depends linearly on the concentration of Fe(II).     

Features of the initiated oxidation mechanism of n-heptadecane at low concentrations of oxygen

The oxidation of n-heptadecane was studied at various partial pressures of oxygen in an oxygen-argon mixture from 100 to 10% and various initiation rates W _i in the range (1–5)·10⁻⁶ mol L⁻¹ s⁻¹ at 413 K. The kinetic curves of oxygen uptake and hydroperoxide buildup were obtained under the indicated conditions. The observed features of n-heptadecane oxidation at low concentrations of oxygen may qualitatively be explained and quantitatively described if the oxidation scheme takes into account the cross termination of alkyl and peroxyl radicals R · + RO₂ · \underrightarrow k₅ \underrightarrow {k_5 } ROOR along with the square termination of peroxyl radicals. A method for determination of the corresponding kinetic parameter by the dependence of the initial oxidation rate on the partial oxygen pressure was proposed. A method for identification of the key reactions and determination of the kinetic parameters by the kinetics of oxygen uptake at lowered oxygen concentrations was developed. The kinetic model of the process was obtained, which quantitatively describes the kinetic curves of oxygen uptake and hydroperoxide buildup at the initial steps of initiated oxidation of n-heptadecane.     

Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: k_obs =a +b[H⁺]. The oxidation of α-deuterioformic acid exhibits a substantial primary kinetic isotope effect (k_H/k_D = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed.     

Complexation of octa(bromophenyl)tetraazaporphyrin with Mn(II) salts in DMF and pyridine

Reactions of octa(bromophenyl)tetraazaporphyrin (H₂OBPTAP) and octaphenyltetraazaporphyrin with Mn(II) acetate and chloride in DMF and pyridine are studied by spectrophotometric method. In the course of formation of octaphenyltetraazaporphyrin complexes, pyridine stabilizes an oxidation state of Mn (+2), and in addition to Mn(II) complex, its radical form is likely to be obtained also in this case. In DMF, the octaphenyltetraazaporphyrinatomanganese(III) complexes are produced. Kinetic studies showed that the complexing capability of Mn acetate in reaction with azaporphyrins drastically differs from that of Mn chloride. H₂OBPTAP does not react with MnCl₂ in pyridine, while its reaction with Mn(OAc)₂ has k_eff²⁹⁸ = (3.1 ± 0.2) × 10^-3 s^-1. Reaction of H₂OBPTAP with Mn(OAc)₂ in DMF occurs instantaneously, whereas in the case of its reaction with MnCl₂, k_eff²⁹⁸ = (1.9 ±0.2) × 10^-3 s^-1.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 1, 2005, pp. 22–27.Original Russian Text Copyright © 2005 by Klyueva, Repina, Chizhova, Berezin.     

Antiradical activity of 5-amino-1,3,6-trimethyluracil in the radical chain oxidation of ethylbenzene as the model system

The antiradical activity of 5-amino-1,3,6-trimethyluracil was quantitatively measured in the initiated radical chain oxidation of ethylbenzene as the model system. The rate constant of the reaction of 5-amino-1,3,6-trimethyluracil with the ethylbenzene peroxyl radical at 333 K was found: k ₇ = (2.1 ± 0.3) × 10⁵ L mol^?1 s^?1. The kinetics of 5-amino-1,3,6-trimethyluracil consumption in the course of the radical chain oxidation of ethylbenzene was studied. The stoichiometric inhibition factor was determined to be f = 2.     

Ionizing-Radiation Ignition of a Hydrogen–Air Mixture

The behavior of a hydrogen–air mixture under the action of ionizing radiation was studied. A kinetic model for radiation-chemical processes in the H₂–O₂–N₂ system was constructed, and the effects of the main parameters of radiolysis on shifting its flammability limits were analyzed. It was found that, under normal conditions (p = 0.1 MPa, T ₀ = 300 K), the ignition of the stoichiometric mixture began at a radiation intensity of about 0.1 kGy/s. The induction period of the chain H₂ oxidation reaction shortened with increasing radiation dose rate and pressure.     

Kinetics of Ketone Oxidation by Ozone in Water Solutions

The spectrophotometric monitoring of ozone consumption in a liquid phase is used to study the kinetics of cyclopentanone and methyl butyl ketone oxidation. The rate of ozone reaction with ketones (RH) at 303–344 K in acidic (HClO₄) aqueous solutions is described by the equation w = k ₁[RH][O₃] + k _En[RH][HClO₄], where k ₁ is the rate constant for the reaction of ozone with RH and k _En is the rate constant for the enolization of RH. The kinetic parameters of the process are found.     

Inhibitory effect of the mixtures of phenol antioxidants and phosphatidylcholine

Phospholipids, phosphatidylcholine from egg yolk (PC) and dipalmitoylphosphatidylcholine, in a complex way affect the inhibitory action of phenol antioxidants (InH) during initiated oxidation of ethylbenzene. At the initial stages of the reaction, phospholipids decrease the efficiency of inhibition by InH. This effect was described satisfactorily with a kinetic scheme that includes the formation of the complex InH · PC, which is inactive in inhibition. The formation of this complex was confirmed spectrophotometrically. Prolongation of the inhibitory effect of the mixture of PC with 4-methoxyphenol compared to the effect of InH alone was found. The effect of PC on the efficiency of inhibition by InH also depends on the duration of the oxidation reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1053–1059, June, 1995.     

Study of the influence of physical aging on macroradical decay in poly(methyl methacrylate)

The macroradical decay in poly(methyl methacrylate) samples with different thermal histories was investigated in the temperature interval 20–100 °C using ESR spectroscopy and the second order kinetic model. The rate constants exhibit two different regimes with the transitions atT _tr=68±1°C which are independent of thermal treatment. ForT<T _tr andT>T _tr the rate constants as well as the corresponding activation parameters are sensitive to history because of different physical microstructures. The compensation law, i.e., the linear relation between lnk _{o, eff} andE _eff, was analyzed in terms of the so-called compensation quantitiesk _c andT _c and a proximity betweenT _c=T _tr andT _o=53±3 °C — Vogel temperature for -segmental dynamics was found. A comparison of kinetic and dynamic data suggests that the decay of terminal macroradicals in the low-temperature region is controlled by secondary relaxations and that the -mobility contributes to a more rapid decay at higher temperatures belowT _g.     

Photooxidation of Ethylbenzene with TiO 2 and Metal Coated TiO 2 and its Kinetics

Photooxidation of ethylbenzene with oxygen to give ethylbenzene hydroperoxide has been achieved in a stirred photochemical reactor that was cooled by a water system by irradiation with a 400W high-pressure mercury lamp and using TiO₂ powder and metal coated TiO₂. The effects of the amount of copper or silver coated on TiO₂ and of the temperature on the rate of oxidation have been investigated. It is suggested that thermal cleavage of the O–O bond and photochemically generated singlet oxygen should be considered as the initiating step in a radical chain mechanism. An optimum loading of 6% Ag or 4–5% Cu was observed for photooxidation of ethylbenzene.     

Photooxidation of Ethylbenzene with TiO<Subscript>2</Subscript> and Metal Coated TiO<Subscript>2</Subscript> and its Kinetics

Summary. Photooxidation of ethylbenzene with oxygen to give ethylbenzene hydroperoxide has been achieved in a stirred photochemical reactor that was cooled by a water system by irradiation with a 400W high-pressure mercury lamp and using TiO₂ powder and metal coated TiO₂. The effects of the amount of copper or silver coated on TiO₂ and of the temperature on the rate of oxidation have been investigated. It is suggested that thermal cleavage of the O–O bond and photochemically generated singlet oxygen should be considered as the initiating step in a radical chain mechanism. An optimum loading of 6% Ag or 4–5% Cu was observed for photooxidation of ethylbenzene.     

Oxidation of Ethylbenzene with Dioxygen in the Presence of Iron(III) Tris(acetylacetonate)-Based Catalytic Systems: 1. Mechanism of Ethylbenzene Oxidation with Dioxygen Catalyzed by Fe(III)(acac)<Subscript>3</Subscript>

The catalytic activity of Fe(III)(acac)₃ (Cat) in ethylbenzene oxidation with dioxygen is studied. 1-Phenylethyl hydroperoxide (PEHP), acetophenone (AP), and methyl phenyl carbinol (MPC) are the main products of the process throughout the Cat concentration range examined. Phenol (Ph) is formed in much smaller amounts. The highest PEHP selectivity, S _PEHP = 65%, is observed at an ethylbenzene conversion of C ≈ 2% at low [Cat] values. PEHP and the other main oxidation products (AP and MPC) form by parallel reactions at any Cat concentration. Depending on [Cat], AP and MPC form by parallel or consecutive reactions. When [Cat] is high enough, AP results from MPC oxidation. At the initial stages of the reaction, the MPC selectivity (S _MPC = 50%) exceeds the PEHP selectivity (S _PEHP = 25–30%). The mechanism of ethylbenzene oxidation catalyzed by Fe(III)(acac)₃ and the role of active complexes in its steps are considered.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 354–359.Original Russian Text Copyright © 2005 by Matienko, Mosolova.     

Kinetic studies of direct blue photodegradation over flower-like TiO<Subscript>2</Subscript>

The kinetics of photocatalytic oxidation reaction for direct blue solution was studied by using flower-like TiO₂ under the irradiation of ultraviolet (UV) light. A series of possible affecting factors were studied, including pH value, the additive amount of light catalyst, H₂O₂ and with or without Ag modification. The kinetics of photocatalytic degradation under UV was found following a pseudo-second-order reaction kinetic model with high regression coefficients (R ²). It has been demonstrated that the initial concentration and its related factors have influenced the photocatalytic degradation efficiency and corresponding kinetic parameters. Also, the kinetic parameter k is increasing with the degradation efficiency.     

Outer‐sphere reduction of hexacyanoferrate(III) by enolizable and nonenolizable aldehydes in alkaline medium

Outer‐sphere reduction of hexacyanoferrate(III) by some enolizable/nonenolizable aldehydes (viz., aliphatic, heterocyclic, and aromatic aldehydes) in alkaline medium has been studied spectrophotometrically at λ_max = 420 nm. The reactions are first order each in [aldehyde] and [Fe(CN)₆^3?]. The rate increases with an increase in [OH^?] in the oxidation of aliphatic and heterocyclic aldehydes, whereas it is independent of [OH^?] in the reaction with aromatic aldehydes. The intervention of free radicals in the reaction mixture was carried out using both acrylonitrile and acrylamide scavenger in two different experiments. The kinetic results indicate that the oxidation of benzaldehyde in aqueous medium proceeds at a slower rate than the aliphatic aldehydes (other than formaldehyde) and furfural. The values of third‐order rate constant (k₃) at 308 K in the oxidations of some aliphatic aldehydes and furfural follow the order (CH₃)₂CH? > CH₃CH₂? > CH₃? > C₄H₃O? > H? . The rate constants correlate with Taft's σ* value, the reaction constant being negative (–9.8). The pseudo–first‐order rate constants in the oxidations of benzaldehyde and substituted benzaldehydes follow the order ? NO₂ > ? H > ? Cl > ? OCH₃. The Hammett plot is also linear with a ρ value (0.6488) for meta‐ and para‐substituted benzaldehydes. The kinetic isotope effect for benzaldehyde (k_H/k_D = 1.93 at 303 K) was obtained. The rate‐determining step is the outer‐sphere formation of Fe(CN)₆^4? and free radicals, which is followed by the rapid oxidation of free radicals by Fe(CN)₆^3? to give products. The kinetic data and hence thermodynamic parameters have been used to distinguish enolizable and nonenolizable aldehydes. An attempt has also been made to correlate kinetic data with hydration equilibrium constants of some aliphatic aldehydes. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 494–505, 2012