The regularities of reversible chain reactions in the equilibrium state

The characteristics of dynamic equilibrium states in the experimentally studied reversible chain reactions of quinoneimines with hydroquinones and in some reversible chain reactions with similar mechanisms are discussed. The concentrations of radicals and non-radical participants were calculated. The equilibrium concentrations of the same reaction participants depend only on the initial reactant concentrations, being independent of the number of chain initiation-chain termination steps in the reaction mechanism. The results of mathematical modeling of reversible chain reactions using the experimentally determined rate constants for elementary steps of a reaction in the quinoneimine-hydroquinone system are presented. Expressions relating the equilibrium constants of elementary steps to each other and to the equilibrium constant of the total stoichiometric reaction are derived. Examples of other actual reversible chain reactions are presented, indicating that such reactions are widespread.     

聚对苯二甲酸乙二酯的热降解和热氧化降解

阐明了聚对苯二甲酸乙二酯缩聚过程中热降解与羧基含量的关系.发现,钛酸四丁酯或草酸亚锡作为缩聚催化剂时,在整个高真空阶段羧基含量并不是一直增加的.采用三种方法(TGA、[η]和COOH)求热氧化降解速度常数,并对其结果进行了讨论.探讨了单一或复合稳定剂和缩聚催化剂对热氧化降解的影响.     

Methanol electrooxidation in alkaline solutions on platinum-based electrodes: Classical and dynamical approach

The electrochemical oxidation of methanol has been carefully studied due to its application in fuel cells. In this work electrooxidation of methanol was investigated on bare platinum electrode, the platinum electrode covered with Nafion and platinum supported on zeolite 13X. Along with classical electrochemical methods, attractor reconstruction was used to make rough distinction among possible reaction mechanisms on different forms of Pt. The obtained transient voltammogram records were used to calculate apparent rate constants for methanol oxidation limiting steps in transient period. All samples contributed to methanol oxidation by basically same reaction mechanism, but with significantly different apparent rate constants.     

Chemodynamics of soft nanoparticulate metal complexes in aqueous media: basic theory for spherical particles with homogeneous spatial distributions of sites and charges

A theoretical discussion is presented to describe the formation and dissociation rate constants for metal ion binding by soft nanoparticulate complexants. The well-known framework of the Eigen mechanism for metal ion complexation by simple ligands in aqueous systems is the starting point. Expressions are derived for the rate constants for the intraparticulate individual outer-sphere and inner-sphere association and dissociation steps for the limiting cases of low and high charge densities. The charge density, binding site density, and size of the nanoparticle play crucial roles. The effects of the electrostatic potential and particle radius on the overall complexation reaction are compared with those for simple ligands. The limitations of the proposed approach for nanoparticulate ligands are discussed, and key issues for future developments are identified.     

Loss of light stabilizers from polypropylene

Loss of light stabilizers. related to 2-hydroxybenzophenone and 2-(2-hydroxyphenyl) benzotriazole. from isotactic polypropylene was measured over the range 60–120° and during storage at 25'. The light stabilizer content in polypropylene corresponded to that used in practice. The rate constants and the activation energy were calculated from the rate of loss. The influence of the structure of stabilizer on the rate of loss from polymer is discussed. The losses of stabilizers from polymer were compared with the vapour pressure of stabilizers and with the losses of stabilizers alone at 280. The rate of diffusion of stabilizers to the surface of polypropylene and the rate of even evaporation may cause a rapid diminution of stabilizer or undesirable accumulation on the polymer surface.     

Electrocatalytic investigation of light-induced electron transfer between cytochrome c6 and photosystem I

A light-activated electron-transfer chain was assembled using solubilized cyanobacterial photosystem I as photoactive enzyme, cytochrome c(6) (also from cyanobacteria) as electron donor, and methyl viologen as electron acceptor. The photocatalytic activity of the ensemble was measured by direct and reversible electrochemistry of cytochrome c(6) at a surface-modified gold electrode. Analysis of the electrochemical response with an appropriate model for the reaction mechanism allowed the relation of the overall catalytic reaction rate to the individual steps of the catalytic cycle. Second-order rate constants were determined for the first time under steady-state conditions. The results validate this approach as an efficient method for the study of electron transfer between photoactive enzymes and their redox partners.     

Polymeric p-benzoquinone–tin derivatives as thermal stabilizers for rigid poly(vinyl chloride). II. Evaluation of the stabilizing efficiency

The polymeric p-benzoquinone-tin derivatives obtained from the reaction of p-benzoquinone with tin tetrachloride in the absence of solvent have been investigated as thermal stabilizers for rigid PVC at 200°C by measuring the rate of dehydrochlorination. The results reveal the greater stabilizing efficiency of the investigated products in relation to dibutyltin maleate and the basic lead stabilizers commonly used in industry. Evidence has been accumulated that the quinone and metallic elements (Sn? Sn bonds) of the stabilizer participate in the stabilization process by trapping the radical intermediates of degradation and blocking the odd electron sites formed on the polymer chains. Although stabilizers with high quinone content provide greater stabilization in the early stages of degradation, their efficiency sharply decreases in subsequent stages. On the other hand, stabilizers of high tin content effectively prohibit the dehydrochlorination reaction at all stages of degradation. On an equivalent basis of metal content, the results clearly demonstrate the greater stabilizing efficiency of tin atoms when found in direct contact in the stabilizer molecule. The mechanism of stabilization suggested to account for the results obtained may be considered as additional evidence in support of the radical nature of the dehydrochlorination reaction.     

Synthesis of hydrated furans: Analysis of the Prins reaction mechanism

Mechanistic analysis of hydrogenated furan synthesis by the Prins reaction was carried out using mathematical modeling. The direct and inverse chemical kinetic problems are solved for the rate constants of all elementary steps. A probable mechanism is derived from the obtained quantitative kinetic parameters and the kinetic patterns of the reaction. These include kinetic curves from the concentration changes of all species in the reaction.     

Some Synergistic Effects of Antioxidants in Natural Rubber

Some synergistic effects of antioxidants in natural rubber were investigated considering results obtained by differencial scanning calorimetry (DSC). Rubber formulations were obtained with mixtures of diaminic(DPPD, IPPD, HPPD) and monoaminic (ADPA, PBN) stabilizers and evaluated. The samples containing the mixture diamine/ADPA stabilizers showed synergistic effects while, for those containing diamine/PBN, no effect was observed. Additionally, the diffusion constants determined by use of vulcanized rubber disks confirmed the molar mass dependence of the stabilizer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reactivity of monoenic and conjugated diene systems present in unsaturated olefin terpolymers—II. Reactions with methyl radicals

The experimental rate constants for the reactions of methyl radicals with model compounds simulating ethylidene-norbornene (ENB), methylene-norbornene (MNB) and isopropylidene-dicyclopentadiene (IPDCP) units in EPDM and EPTM elastomers are reported. These constants, as well as others reported in a previous paper or derived from the literature, have been used to perform a kinetic analysis of the grafting of styrene onto EPM, EP-ENB or EP-IPDCP in inert solvent. The systems of kinetic differential equations have been solved by numerical integration without steady state approximation. Valuable information has been obtained on the role of the nature of radical initiators and the sensitivity of the results to change with constants in the various steps.     

二(烷基黄原酸)合铂(Ⅱ)与哌啶在苯介质中连串取代反应的动力学及机理

研究了二(境基黄原致)合铂(Ⅱ)[Pt(S₂COR)₂(R=Me,Et,n-Pr,n-Bu,Am)]与哌啶连串取代反应动力学,提出了包括前期平衡的反应机理,据此导出的速率方程圈满地解释了全部实验事实.计算了前期平衡常数和速控步骤的速率常数,并对加成物的结构作了合理推断,计算了各活化参数和两个反应系的等动力学温度β₁=283±7K和β₂=263±25K.     

Mathematical modeling of butadiene rubber synthesis process on neodymium-containing catalyst system

The synthesis of butadiene rubber mediated by a lanthanide catalyst system based on neodymium(III) chloride in a batch reactor was mathematically modeled. The mechanism of the process was identified and the rate constants of various reaction steps were determined. It was found that chain transfer reactions with different rate constants have an effect on the molecular-mass characteristics of butadiene rubber.     

Automation of the information content analysis of kinetic parameters

The aim of this work has been to automate the analysis of kinetic measurements in solving inverse problems in order to recognize the number and form of the independent combinations of reaction rate constants. Software for determining the basis of nonlinear parametric functions of the kinetic parameters of a mathematical model for the mechanism of a complex chemical reaction has been developed and described. The main stages of program construction with the use of a search algorithm for the independent combinations of the rate constants of elementary steps in the mechanism of a complex chemical reaction based on experimental data on the concentrations of reactants are considered.     

Computational techniques applied to the study of the oxidation kinetics of iron and molybdenum cyanocomplexes by peroxynitrous acid

The oxidation kinetics of iron and molybdenum cyanocomplexes by peroxynitrous acid were studied by computational techniques. The rate constants of ONOOH decomposition and substrate oxidation were calculated by fitting the experimental data to the solution of the ordinary differential equations mechanism. There is a linear relationship between the rate constants which is solved by varying the initial concentration of one of the reactive species. The rate constants of the steps involved in ONOOH decomposition were also determined following the same procedure and considering a linear relationship between the rate constants. The results are consistent with the values previously found using the conventional method of integration, and they validate the prior steady state assumption. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of irradiation on oxygen-containing compounds in the presence of olefins

The relation between the structure of olefins and oxygen-containing compounds and their reactivity in radical addition, substitution and isomerization processes under γ-irradiation in a wide temperature range was examined. Correlation equations for the determination of elementary rate constants and their Arrhenius parameters are given. The compensation effect is discussed. A mechanism of product formation is proposed and the corresponding kinetic equations are derived from the steady-state principle.     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XIII: Eugenol (4-allyl-2-methoxy-phenol)

Eugenol (4-allyl-2-methoxy-phenol) has been examined as a thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high thermal stability value (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium-zinc soap and octyl tin mercaptide.Blending this organic stabilizer with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate together with the longer extent of discolouration of PVC stabilized by eugenol as compared with the blank and the samples stabilized with reference commercial stabilizers.A probable mechanism for the stabilizing action of eugenol has been proposed. The stabilizing efficiency is attributed partially to the stabilizer's ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.     

Kinetic Studies on Ligand Substitution Reactions of Metallothioneins with DTPA and EDTA

Cd, Zn-thionelns were isolated from the rat liver by improved Winge method and purified further. The composition was determined. The mobilization of Cd ions from the Cd, Zn-metallothioneins was studied with spectrophotometric method. The results show that the reaction of DTP A or EDTA with Cd, Zn-thioneins occurs through three steps. The first step follows pseudo-first order reaction with association mechanism. The formation constants and the dissociation rate constants of the relevant intermediate ternary complexes and apparent rate constants, Kapp were determined. The properties and structure of Cd, Zn-thioneins and ligands with low molecular weights affect the values of Kapp.     

The effect of tin stabilizers on the thermal degradation of poly(vinyl chloride)

Simultaneous HCl evolution and spin-generation measurements were made on poly(vinyl chloride) (PVC) samples containing stabilizers of the type R_x Sn Y_4-x. It was found that tetrabutyltin and tributyltin laurate were better stabilizers than dibutyltin dilaurate. On the basis of the results, a mechanism for the stabilization of PVC by this class of compounds is proposed.     

从聚合物分子量及聚合动力学参数计算链转移常数

在研究自由基聚合反应动力学时,将单体浓度、引发剂浓度和溶剂浓度之间的摩尔比相对固定,并使之同步改变,由此获得一系列的R_p值。从时间—聚合转化率关系各直线部分截取转化率低于0.10质量分数、相对偏差小于±0.010质量分数的聚合物,测定它们的数均相对分子质量,于是关系式: 1/ _n=R_t/R_p+∑R_(tr)/R_p被简化为1/ =R_t/R_p+K链终止方式可从附表中判定。从1/ =k_1/K_p~2·R_p/c~2(M)+K(双基终止),1/ =k'_1/K_p·1/c(M)+K(单基终止)、或1/ =1/2·fk_dk_(prt)/(K_1·K_2)·c(I)/c~2(M)+K(初级自由基终止)计算出k_t/k_p~2·k_1'/k_p或1/2·fk_dk_(prt)/(k_1·k_p)值,并在各给定的实验条件下得C_1、C_s和C_M值。本文详细地阐述了1/ =K和1/ ≠K条件下计箅C_I、C_s和C_M值的实例。并由此佔价链转移反应机理。     

烷基黄原酸合钴(III)与二丙胺第三步反应动力学

配合物中心离子可能起到一个模板的作用将配体的反应基团拉到特定位置，以产生空间选择性的多级反应．Fadkler等人[1]发现与过渡金属管合的黄原酸粮的OR基可以与仲胺发生取代反应．王安周等人间用高效液相色谱法研究了Co（S2COR）3与二甲胺在正己烷中的取代反应动力学，发现该反应为连串反应，逐步生成Co（S2oCOR）2（S2CNMe2），Co（S2COR）（S2CNMe2）2和Co（S2CNMe2）3该文只研究第一步取代反应，由于混配配合物纯品很难制备，至今对其取代反应动力学的研究报导较少．Martin等人间合成的双核自己合物［Co（SZCNEt）。］B…