Dependence of the rate of photocatalytic decomposition of safranine on the catalyst concentration

The effect of the concentration of disperse titanium-containing oxide photocatalysts on the decomposition of safranine in aqueous solution was studied. The observed decomposition rate constant of safranine increases with increasing catalyst content in the solution and reaches a maximum at catalyst concentration ≤3 g/L, after which this constant no longer depends on the catalyst content. The plateau for the rate constant results from light scattering and narrowing of the reaction space due to increased optical density of the solution. An increase in the specific catalyst surface is observed in the region of a rising rate constant with increasing catalyst concentration, while no such dependence is found in the plateau region. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 104-107, March-April, 2009.     

Kinetics of Radical Polymerization. XXIX. Kinetics of Initiation in the Polymerization of Ethyl Acrylate

The rate of initiation has been investigated in the free-radical polymerization of ethyl acrylate at 50°C in two solvents, benzene and dimethylformamide. The rate constant of initiation and the rate constant of the decomposition of AIBN was determined by the inhibition method and nitrogen volumetry, respectively. The rate constant of initiation was found to be constant over the whole range of monomer concentration in benzene solutions, but it proved to depend on the concentration of monomer in dimethylformamide solutions. The latter dependence is not linear. It was pointed out that the change in the rate constant of initiation is due to the solvent effect on the rate constant of decomposition of AIBN, because the factor of radical efficiency is practically constant over the whole range of monomer concentration. The observed relationship between the rate constant of initiation and the molar fraction of monomer was interpreted on the basis of the selective solvation of initiator molecules.     

Thermal decomposition of N-substituted N-methylnitroamines

Thermal decomposition of the N-methylnitroamines based on azoles in the liquid phase proceeds as a first-order reaction and is limited by the homolysis of the N-NO₂ bond. The reaction rate is affected by the steric effect of the azole substituent. The activation parameters for the limiting stage of thermal decomposition were determined, and correlations between the logarithm of the rate constant, activation energy, and the steric constant E _s of the substituent were elucidated.     

Effect of medium on the rate constant of decomposition of di(tert-butyl)trioxide

It was found that the medium affects the rate constant of the thermal decomposition of di(tert-butyl)trioxide. In all solvents studied, the decomposition occurred according to the first-order law. The effect of the solvent on the rate constant was analyzed within the framework of the Koppel-Palm equation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1167–1168, June, 1995.The authors are grateful to O. N. Makarova for help in this work.This study was financially supported by the Russian Foundation for Basic Research (Grant No. 93-03-5231).     

Structural and kinetic regularities of thermal decomposition of <Emphasis Type="Italic">gem</Emphasis>-trinitromethylazoles in the liquid phase

Kinetics of liquid-phase thermal decomposition of a series of triazoles and tetrazoles containing a gem-trinitromethyl group were studied by manometry and photoelectrocolorimetry, and the mechanism of the thermal decomposition was established. The activation parameters of the rate-limiting stage of the process were evaluated. It was shown that the thermal stability of the gem-trinitromethyl group varies over a broad range, depending on the steric effect of the azole. The rate constant and activation energy correlate with the steric effect of the azole. The thermal decomposition of β-trinitroethylaminotetrazoles proceeds heterolytically with initial dissociation of the C-C bond to give a carbocation and the nitroform anion.     

Formation and decomposition of a volatile Zn-containing complex for the synthesis of ZnO films

The formation of a Zn-containing complex on a ZnO target in an H₂O₂ vapor medium, the sublimation of this complex, and the decomposition of the complex to the original compound are considered. UV preirradiation of the target raises the concentration of the Zn-containing complex in the gas phase in proportion to the irradiation time. The rate constant of the decomposition of the complex on a substrate is reported. The activation energy and the preexponential factor (k ₀) for the decomposition reaction are derived from the temperature dependence of the rate constant. The fact that the activation energy of the decomposition of the complex is similar to that of hydrogen peroxide decomposition suggests that the complex has a peroxide-like structure. The experimental and calculated k ₀ data indicate that the decomposition reaction is monomolecular.     

Stability of Oligomeric α-Alkoxyhydroperoxides

The thermal decomposition of oligomeric -alkoxyhydroperoxides (I) is described by a first-order rate law and characterized by an activation energy equal to 19.7 kJ/mol. A chain mechanism and a rate law for this reaction are proposed. The effect of amine and phenolic stabilizers on decomposition is studied, the efficiency of phenolic stabilizers is examined, and the effective rate constant of the acid-catalyzed decomposition of compounds I is determined.     

Decomposition kinetics of free radical initiators in micellar solutions

The kinetic parameters of thermal decomposition of initiators, azo-bis-isobutyronitrile (AIBN) and dicyclohexyl peroxydicarbonate (PC), have been measured in aqueous micellar solutions of sodium dodecylsulfate (SDS), cetyltrimethylammonium bromide (CTAB), and egg lecithin. The inhibitor technique and acceptors of free radicals have been used to estimate the efficiency of the initiation during AIBN decomposition. The rate constant of PC decomposition in a SDS micellar solution is the same as inn-decane. CTAB and lecithin accelerate the rate of PC decomposition. Mechanisms of surfactant effect on the PC decomposition are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1752–1757, October, 1994.The work was financially supported in part by the International Science Foundation (ISF) (Grant No. MAQ 000).     

The kinetics and mechanism of induced thermal decomposition of peroxomonosulphate by phase transfer catalysts

The kinetics of induced decomposition of potassium peroxomonosulphate (PMS) by the phase transfer catalysts (PTC), viz. tetrabutylammonium chloride [TBAC] and tetrabutylphosphonium chloride [TBPC] have been investigated. The effect of [PMS], [PTC], ionic strength of the medium and temperature on the rate of decomposition of PMS was studied. The rate of decomposition of PMS was monitored under pseudo-first-order condition at a constant temperature (50 ± 0.1 °C). The rate of decomposition was first order with respect to PMS for TBAC and half order for TBPC. The order with respect of PTC was found to be unity for TBAC and half order for TBPC. A suitable kinetic scheme has been proposed to account for the experimental data and its significance is discussed.     

Thermal decomposition of solid azobisisobutyronitrile

The rate of the thermal decomposition of solid azobisisobutyronitrile was measured under conditions such that the side processes, such as gas-phase decomposition, the formation of liquid products, crystal cracking, and polymorphic transitions, had no effect on the process rate. The reaction occurs on the inner crystal surface, and its rate depends on the method of crystallization. The sample crystallized under conditions of low supersaturation is the most stable. The kinetic parameters of the reaction are E = 134.9 ± 3.5 kJ/mol and log A = 14.12 ± 1.5 [s^?1]. The decomposition rate constant of solid azobisisobutyronitrile is 50 times lower than that of azobisisobutyronitrile in benzene solution. The low reaction rate in the solid phase is explained in terms of the additional-volume model proposed for unimolecular reactions in molecular crystals.     

Significance of the kinetics of thermal decomposition of NaHCO3 evaluated by thermal analysis

The Arrhenius parameters and kinetic obedience were determined by TG at constant temperatures as well as at linearly increasing temperatures for the thermal decomposition of sodium hydrogencarbonate. Effects of the sample size (0.5–10 mg) and the particle size on the rate behavior were examined. With such a sample size smaller than ca. 5 mg, an effect of the heating rate was not so critical as is the case with the larger sample size. The Arrhenius parameters and kinetic obedience determined by use of the Ozawa method were in excellent agreement with those determined isothermally. The activation energyE determined with ca. 1 mg of sample was nearly constant independently of the fractional reactiona. Any change in the Arrhenius parameters with different experimental conditions was dicussed in connection with the kinetic compensation effect.     

Emulsion polymerization of vinyl chloride, 2 potassium persulfats decomposition in the presence of PVC latex

The decomposition rate of potassium persulfate (KPS) in aqueous solutions, in the presence of sodium dodecyl sulfate (SDS) and poly(vinyl chloride) latex (PVC) was studied. The dissolved SDS increases the decomposition rate constant (k_d) while the SDS aggregation as micella and/or its adsorption on the polymer hydrophobic surface results in a decreasing k_d. The emulsifier - free surface of the polymer particles increases the decomposition rate. A reaction mechanism based on emulsifier - emulsifier and emulsifier - polymer hydrophobic interactions is put forward.     

DMP与DEP在凝聚相中裂解反应理论研究: 隧道效应与溶剂效应

采用密度泛函理论(DFT)B3LYP方法, 以极化连续模型(PCM)和导体反应场模型(COSMORS)的溶剂模型为基础, 结合反应动力学研究了2,2-二甲氧基丙烷(DMP)与2,2-二乙氧基丙烷(DEP)在凝聚相(溶液相)中的裂解反应. 结果表明, 四元环过渡态裂解反应机理是DMP与DEP裂解反应的主反应通道, 溶剂效应和隧道效应对液相中的裂解反应速率有较大的影响, 而且溶剂效应的影响更显著. 在凝聚相反应理论研究中, 溶剂效应和量子隧道效应都是不能忽略的因素.     

Kinetics of Copolymerization. III. Determination of the Rate of Initiation in the Copolymerization System Acrylonitrile/Methyl Acrylate/Dimethylformamide

For the AIBN-initia ted copolymerization System acryionitriie/methyl methacrylate/dimethylformamide, the dependence of the composition of the monomer mixture on the rate constant of initiation and that of the initiator decomposition has been inves-tigated at 313, 323, and 333° K. It was established that the rate constant of initiator decomposition is independent of, while that of the initiation is dependent on, the composition of the monomer mixture. The efficiency of initiation has been calculated and its value was found to be somewhat altered not only by the composition of the monomer mixture but also decreased siightiy with an increase of temperature.     

Non-adiabatic unimolecular dissociation of polyatomic molecules. III. The decomposition of dioxetane

The general theory presented in part I is applied to a “large” molecule: the decomposition of chemically activated ethoxy-1,2-dioxctane into formaldehyde and ethyl formate. Microcanonical (specific-energy) rate constants for dioxetane decomposition are calculated at total energies of 2.5, 7.5 and 10.0 kcal/mole. It is found that the presence of selection rules increases the rate constant, but this effect decreases rapidly as the energy increases. The rate constant is shown to be proportional to the average effective total number of final states at a given energy, which is a form of a phase space theory result. Estimated value of the rate constant under experimental conditions is calculated to be in the range 10⁹–10¹¹ s^?1, which agrees reasonably well with the experiment estimate ?10⁸ s^?1.     

Über die Kinetik der thermischen Zersetzung einiger Pikolinkomplexe des Nickel(II)Bromids

The thermal decomposition of nickel bromide-picoline complexes has been studied under dynamic conditions, using constant heating rate. A comparison with the results reported in an earlier paper for the corresponding chloride complexes shows the effect of the halogen on the mechanism of thermal decomposition.     

NF3 decomposition behind shock waves in the intermediate pressure range

Rates of NF₃ thermal decomposition in the temperature range 1450–2050 K and pressure range 1.2–4.2 atm were measured by a shock tube technique. NF₃ decomposition was monitored by UV absorption of the produced NF₂ radicals. The bimolecular rate constant of the NF₃ decomposition reaction essentially depends upon pressure. An empirical formula was obtained from the experimental data which correctly expresses the dependence of the measured rate constant of decomposition upon the temperature and pressure of the reacting mixture behind the shock wave.     

Influences of evolved gases on the thermal decomposition of zinc carbonate hydroxide evaluated by controlled rate evolved gas analysis coupled With TG

The influences of atmospheric CO₂ and H₂O on the kinetics of the thermal decomposition of zinc carbonate hydroxide, Zn₅(CO₃)₂(OH)₆, were investigated by means of controlled rate evolved gas analysis (CREGA) coupled with TG. Although CO₂ and H₂O were evolved simultaneously in a single mass-loss step of the thermal decomposition, different effects of those evolved gases on the kinetic rate behavior were observed. No distinguished effect of atmospheric CO₂ was detected within the possible range of self-generated CO₂ concentration. On the other hand, apparent acceleration effect by the increase in the concentration of atmospheric H₂O was observed as the reduction of reaction temperature during the course of constant rate thermal decomposition. The catalytic effect was characterized by the decrease in the apparent activation energy for the established reaction with increasing the concentration of atmospheric H₂O, accompanied by the partially compensating decrease in the pre-exponential factor.     

Kinetics and mechanism of thermal decomposition of ammonium nitrate and sulfate mixtures

Fundamental kinetic aspects of the decomposition of mixtures and double salts of ammonium nitrate and ammonium sulfate were studied. The effect of water and sulfuric acid additives on the thermal decomposition rate of ammonium nitrate and sulfate mixtures was examined. The constant of proton exchange between nitric acid and the sulfate anion in molten ammonium nitrate was estimated.     

Thermal decomposition of gem-dinitroethylnitramines

Thermal decomposition of C,N-disubstituted gem-dinitroethylnitramines in dilute solutions in inert solvents is a first-order reaction and it is unaffected by the polarity of the solvent. The rate constant is largely controlled by the steric effect of the substituent at the carbon atom bearing gem-nitro groups. A correlation is found between the rate constant and the steric constant E _s of the substituent. This correlation permits prediction not only of thermal stability of yet unexplored compounds, but also of change of the decomposition mechanism.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1669–1673.Original Russian Text Copyright © 2004 by Stepanov, Kruglyakova, Astakhov.This revised version was published online in April 2005 with a corrected cover date.