混合溶剂中trans-[CoCl2(NH3)4]+与Fe2+反应的电子转移机理

用Vnion Giken Model RA-401 Stopped-flow spectrophotometer 测定了在H_2O-MeOH,H_2O-EtOH,H_2O-PrOH,H_2O-DMSO,H_2O-DMF,H_2O-HMPA,H_2O-THF和H_2O-Dioxane等混合溶剂中,trans-[CoCl_2(NH_3)_4]~+与Fe(Ⅱ)间电子转移反应的速度常数。实验结果表明,表观二级进度常数K_(app)与[H~+]无关;混合溶剂的性质明显的影响K_(app);在所有实验中K_(app)(图4—7)先随x_(03)增大而增大,然后,随x_(03)继续增大而又下降;在x_(03)较小时,InK_(app)随溶剂介电常数的倒数D~(-1)增大而增大。上述事实说明反应的第三步是速控步骤。     

Exclusion of aromatic radical cations from cyclodextrin nanocavity studied by pulse radiolysis

The influence of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the one-electron oxidation reaction of aromatic sulfides (S) with Br2*- and the decay process of the S radical cation (S*+) was investigated by pulse radiolysis. The dissociation kinetics of S*+ from the CD cavity was examined in terms of the apparent equilibrium constants (Kapp) for the formation and decay processes of S*+. Inhibition of the one-electron oxidation reaction of S by Br2*- was clearly observed in the presence of HP-beta-CD. On the basis of a comparison between the determined Kapp values, it was found that the binding ability of S*+ with HP-beta-CD is much lower than that of S, because of the hydrophobic nature of the cavity. The formation process of the dimer radical cation of 4-(methylthio)phenylmethanol ((MTPM)2*+), which is generated between MTPM(*+) and neutral MTPM in solution, was also inhibited by the addition of HP-beta-CD.     

Determination of apparent binding constants of drugs by capillary electrophoresis using beta-cyclodextrin as ligand and three different linear plotting methods

Capillary electrophoretic estimation of apparent binding constants (Kapp) for naproxen, salbutamol, indomethacine and procaine with beta-cyclodextrin is presented. While with naproxen and indomethacine this approach was straightforward and gave well compatible results by three different linearization plots (double reciprocal, x reciprocal and y reciprocal), with salbutamol a higher value than reported for the electromigration estimation of this magnitude was obtained (a fourfold increase). This difference is ascribed to the fact that the measurements were done in the acid region (while the reported values were obtained at higher pH values). As a matter of fact the values of Kapp, reported in this communication for salbutamol comply better with the value of Kapp (69.3) obtained by the solubility method.     

Gallium(III)/4-(2-pyridylazo)resorcinol system in water and SDS solution: kinetics and thermodynamics

The equilibria and kinetics of the complex formation and dissociation reaction between gallium(III) and PAR [4-(2-pyridylazo)resorcinol] have been investigated in water and in the presence of SDS micelles. The reactive form of Ga(III) is GaOH2+ in both cases. The addition of SDS results in an increase of both the binding affinity and velocity, the maximum accelerating effect being observed just above the cmc value of SDS that, under the conditions of the experiments, is 5.6 x 10-3 M. At pH = 3.2, the maximum value of the equilibrium constant ratio Kapp(SDS)/Kapp(H2O) is 27.4, whereas that of the binding rate constants kf(SDS)/kf(H2O) is 16. The results are interpreted in terms of increased concentrations of the reactants on the micelle surface and on competition of PAR and SDS for GaOH2+.     

热动力学方法的研究Ⅰ. 反应速率常数、活化能的量热法测定

用流动型微量量热法测定了在不同温度下乙酸和甲醇及乙醇的酯化反应的速率常数, 并籍助于阿累尼鸟斯公式测定了这些反应的活化能。为了检验此方法的可靠性, 测定了乙酸甲酯和乙酸乙酯水解反应(酯化反应的逆反应)的速率常数, 这一实验结果与根据酯化反应实验数据计算得到的结果相一致。     

Rate and equilibrium constants for Grignard reaction with alkoxysilanes and ketones

Kinetics of tetraethoxysilane reaction with n-butylmagnesium chloride, specifically solvated with dibutyl ether, diethyl ether, THF, and triethylamine, was studied in toluene. Also isopropylmagnesium chloride, isopropyltriethoxysilane, and diisopropylketone were involved in a similar investigation. The pseudo-first-order rate constants determined at a great excess of these organomagnesium compounds were used for separation of the appropriate equilibrium and rate constants. An advantage of the method consists in preclusion of non-specific solvation effects when effects of donor solvents are considered. In separate experiments, thermodynamic parameters were determined for rate and equilibrium constants, measured for the reaction of tetraethoxysilane with n-butylmagnesium chloride solvated with dibutyl ether in toluene, and also in bulk dibutyl ether. The implication of steric and solvation effects on this reaction is discussed.     

Determination of electrochemical kinetic parameters from the measurement of faradaic impedance during the growth of the dropping mercury electrode

The electrochemical kinetic parameters of the V(II)/V(III) couple in HBr solutions of different concentrations were determined from the measurement of faradaic impedance as a function of time during the growth of the dropping mercury electrode. The same method of analysis was applied to the study of the effect of uncharged surfactants on the electrode reaction of Cd(II) in 1 M NaNO₃ solutions. The rate constant of the vanadium system decreased with increasing concentration of HBr; this change of the rate constant was discussed in terms of the Frumkin double-layer effect. The relationship between the rate constant of Cd(II) and coverage of the surfactants was not linear, and followed the equation based upon Parsons' model of the blocking effect. The conditional rate constant of Cd(II) in the absence of surfactants was determined to be 0.6–1.1 cm s^?1 from the dependence of the rate constant on the coverage.     

阳极溶出伏安法测定氨羧配合物的组成与稳定常数

本文用阳极溶出伏安法研究氨羧配合物,采用最小二乘曲线拟合和统计权重平均等程序处理实验数据,测定了三乙四胺六乙酸(TTHA)、氨三乙酸(NTA)和乙二胺四乙酸(EDTA)与Pb(Ⅱ)、Cd(Ⅱ)和Zn(Ⅱ)离子所生成的配合物的稳定常数和组成。测定结果与文献值相符。     

Calorimetric Reaction Rate Determination with the Characteristic Kinetic Parameter Method

On the basis of the theory of thermokinetics proposed in the literature, a novel thermokinetic method for determination of the reaction rate, the characteristic parameter method, is proposed in this paper. Mathematical models were established to determine the kinetic parameters and rate constants. In order to test the validity of this method, the saponifications of ethyl benzoate, ethyl acetate and ethyl propionate, and the formation of hexamethylenetetramine were studied with this method. The rate constants calculated with this method are in agreement with those in the literature, and the characteristic parameter method is therefore believed to be correct.In the light of the characteristic parameter method, we have developed further two thermo-kinetic methods, the thermoanalytical single and multi-curve methods, which are convenient for simultaneous determination of the reaction order and the rate constant. The reaction orders and rate constants of the saponifications of ethyl acetate and ethyl butyrate and the ring-opening reaction of epichlorohydrin with hydrobromic acid were determined with these methods, and their validity was verified by the experimental results.This revised version was published online in November 2005 with corrections to the Cover Date.     

N溴代丁二酰亚胺氧化醇反应的热动力学研究

氧化反应是有机化学中的一种重要反应类型,也是有机化学、化学工程和生物学家们研究的重点之一.但因其机理复杂,至今未见到用热动力学理论探索氧化反应体系的报道. N溴代丁二酰亚胺(NBS)是良好的溴化试剂,在不同反应条件下,它既可和不饱和键发生加成反应,也可在水溶液中作为次溴酸的来源,还可作为有效的氧化剂和脱氢剂.Reich和Reichstein首先报道了用N溴代乙酰亚胺将仲醇缓慢氧化为酮,Fieser等人报道了NBS的氧化作用.本文用RD-1型热导式自动量热计研究了35℃下NBS氧化异丙醇及环己醇2个反应体系,计算了反应速率常数,对反应的动力学及其机理提出了较合理的解释.     

Kinetics of the interaction of Cd(II)-histidine complex with ninhydrin in absence and presence of cationic and anionic micelles

Kinetics of the interaction of Cd(II)-histidine complex with ninhydrin has been carried out at pH 5.02 (acetic acid-sodium acetate buffer) under varying conditions of reactant concentrations, temperature, and surfactant concentrations. The order of the reaction with respect to Cd(II)-histidine complex was unity while it was fractional with respect to ninhydrin. On the basis of these studies a mechanism has been proposed. In the absence of the surfactants, the reaction followed rate equation: while, in presence of surfactants, the following rate equation was obeyed: Anionic micelles of sodium dodecyl sulphate catalyze the reaction with the rate reaching a maximum at ca. 0.10 mol dm⁻³ surfactant. The surfactant decreases activation enthalpy and makes it more negative. Cationic micelles of cetyltrimethylammonium bromide strongly inhibit the reaction and increase the activation enthalpy but make the activation entropy more positive than the SDS micelles. Added salts (KNO₃ and NaCl) inhibit the catalysis, and the effect is more with the latter. The rate constants, binding constants with surfactants, and the index of cooperativity have been evaluated. © 1997 John Wiley & Sons, Inc.     

Investigation of dynamics of radiolytic formation of CdSe nanoparticles in aqueous solutions

The formation of cadmium selenide, CdSe, nanoparticles in aqueous solutions containing equimolar ammoniated cadmium sulfate, [Cd(NH(3))](4)SO(4) and sodium selenosulfate, Na(2)SeSO(3) as the starting materials, has been investigated by electron pulse radiolysis coupled with kinetic spectrometry. The formation of CdSe nanoparticles was found to proceed through the generation of short-lived transient intermediate species having an absorption peak at 520 nm, which is formed only upon the reaction of hydrated electrons, e(aq) with the precursor ions under deaerated conditions. The transient intermediate species decays with a weighted average rate constant, 1.2 × 10(7) s(-1). The transient intermediate species formed in the case of individual precursors did not match with the transients formed when both the precursors are taken together in the solutions under the present experimental conditions. The reaction rate constants between the precursor ions, [Cd(NH(3))(4)](2+) and the transient intermediate species formed from [SeSO(3)](2-) was 1.9 × 10(10) M(-1) s(-1). Similarly, the reaction rate constants between the precursor ions, [SeSO(3)](2-) and the transient intermediate species formed from [Cd(NH(3))(4)](2+) was 5.5 × 10(10) M(-1) s(-1). This clearly indicates that the formation of CdSe nanoparticles occurs through both reaction channels. However, the major reaction channel is through the reaction of e(aq) with the [Cd(NH(3))(4)](2+) ions (k = 3.1 × 10 (10) M(-1) s(-1)), as its rate constant is one order higher than that of the reaction of e(aq) with the [SeSO(3)](2-) ions (k = 2.3 × 10(9) M(-1) s(-1)).     

Kinetics of adsorption and desorption of sodium alkyl sulfates to and from nylon particles

The desorption rate of surfactant ions from nylon particles was investigated at the concentrations below the critical micelle concentration by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. The surfactants used were sodium decyl, sodium dodecyl, sodium tetradecyl, and sodium hexadecyl sulfates. The desorption rate was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme. The adsorption rate constants were estimated from the experimental desorption rate constants and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined to be 1–6 sec^–1 and the adsorption rate constants to be 2–8×10⁴ mol^–1 dm³ sec^–1; the former decreased and the latter increased with increasing number of carbon atoms in alkyl chain of the surfactants.     

Amperometrically indicated pseudotitrations"--II. Determination of chromium(III) in the presence of other reacting metal ions

Chromium(III) may be determined complexometrically in a pseudotitration in which no reaction takes place in the bulk of the solution. Redox catalyzed titration reaction proceeds only in the vicinity of the indicating electrode. The titration curves for solutions containing additional metal ions which react with EDTA are discussed and classified according to their reduction potentials, equilibrium, constants and reaction rates. In certain combinations two or more metals may be determined simultaneously from one titration curve. Examples given are Cr/Hg, Cr/Cd, and Cr/Zn.     

Evaluation of cadmium species lability using ion-pair reversed phase HPLC coupled on-line with inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) coupled on-line with an ion-pair reversed phase HPLC (IP-RP HPLC) was developed for determining the lability of Cd species. The IP-RP HPLC-ICP-MS system measures chromatographic behaviors of Cd species in the presence of different model complexing agents (L) with stability constants (log K_CdL) from 3.8 to 19.0. Cd species with log K_CdL higher than 16, between 8 and 16, and smaller than 8 was then classified into inert, moderately labile, and labile species, respectively. The conditional stability constants and dissociation rate constants were also estimated from their corresponding chromatographic behavior. This method was applied to evaluating the lability-dependent biouptake of different Cd species in Phaeodactylum tricornutum, a typical unicellular marine diatom. IP-RP HPLC-ICP-MS is a useful and promising technique for determining the lability of noncovalent-bonded metal species (such as Cd species) in the environment and for forecasting their corresponding bioavailability especially when their speciation cannot be rigorously controlled and measured.     

Kinetic approach to radiation-induced grafting in the polyethylene–styrene system. II

The investigation method reported in the previous paper was applied to four reaction methods: preirradiation method with reaction in liquid monomer, preirradiation method with reaction in monomer vapor, simultaneous irradiation method in liquid, and simultaneous irradiation method in vapor. The increasing patterns and values of the degree of grafting experimentally obtained roughly agreed with those calculated by using the same rate constants. At high monomer concentration, the rate of grafting was small; at low monomer concentration, the rate of grafting was large. Strictly speaking, the data by simultaneous irradiation method were somewhat larger than those by calculation. Two additional factors, as homopolymerization and the grafting from the radicals formed on the grafted polystyrene, were considered and discussed. The rate constants obtained were also discussed.     

用微电极上的光谱电化学法测定催化反应的速率常数

首次采用微电极上的光谱电化学法测定了K_4Fe(CN)_6-抗坏血酸、K_4Fe(CN)_6-组氨酸体系的催化反应速率常数。实验发现, 当抗坏血酸或组氨酸的浓度同K_4Fe(CN)_6的浓度相当甚至稍低时, 仍可按准一级化学反应来处理, 并提出了合理的解释。     

Synthesis of 2-Methoxy-3-pentene in a Liquid Phase over a Sulfoionite Catalyst: II. Kinetic Model of Reactions Occurring in the Synthesis

The kinetics of 2-methoxy-3-pentene synthesis from 1,3-pentadiene isomers and methanol was considered. Reaction rates were measured experimentally, and the compositions of reaction mixtures were determined by chromatography. Reaction rate constants and the activation energy of the main reaction were determined experimentally.     

Rate constants for the reaction of OH radicals with some amino polycarboxylic acids

Rate constants of OH radical reaction with some amino polycarboxylic acids (APCAs) such as EDTA, DTPA, HEDTA, NTA, and HIDA have been determined at different pHs using pulse radiolysis competition kinetics method with thiocyanate as the reference solute. The rate constants varied with pH (possibly due to their various pKs) and the plots of rate constants vs. pH are given. Rate constants for OH radical reaction with the various acid–base forms of these amino polycarboxylic acids are estimated from the plateau values in the plots. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 99–104, 2000     

Overall rate constant measurements of the reaction of chloroalkylperoxy radicals with nitric oxide

The overall rate constants of the NO reaction with chloroalkylperoxy radicals derived from the Cl-initiated oxidation of several atmospherically abundant alkenes-ethene, propene, 1-butene, 2-butene, 2-methylpropene, 1,3-butadiene, and isoprene (2-methyl-1,3-butadiene)-were determined for the first time via the turbulent flow technique and pseudo-first-order kinetics conditions with high-pressure chemical ionization mass spectrometry for the direct detection of chloroalkylperoxy radical reactants. The individual 100 Torr, 298 K rate constants for each monoalkene system were found to be identical within the 95% confidence interval associated with each separate measurement, whereas the corresponding rate constants for 1,3-butadiene and isoprene were both approximately 20% higher than the monoalkene mean value. Our previous study of the reaction of hydroxylalkylperoxy radicals (derived from the OH-initiated oxidation of alkenes) with NO yielded identical rate constants for all of the alkenes under study, with a rate constant value within the statistical uncertainty of the value determined here for the NO reaction of chloroalkylperoxy radicals derived from monoalkenes. Thus, the reaction of NO with chloroalkylperoxy radicals derived from dialkenes is found to be significantly faster than the NO reaction with either chloroalkylperoxy radicals derived from monoalkenes or hydroxyalkylperoxy radicals derived from either mono- or dialkenes.