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.     

Kinetics and Thermodynamics of Synthesis of Hybrid Oligomer‐Acrylated Cycloaliphatic Epoxy in the Presence of Triphenylphosphine and Triethylamine Catalysts

The kinetics for the esterification of cycloaliphatic epoxy resin with acrylic acid was investigated in the presence of two different catalysts, namely triethylamine (TEA) and triphenylphosphine (TPP). The reactions were carried out at four different temperatures in the range of 80–110°C and 60–90°C for TPP and TEA catalysts, respectively. The power law kinetics model was adopted for analyzing experimental data to determine reaction equations. Both differential and integral methods were applied to determine the reaction orders and reaction constants. The overall reaction order for the reaction systems was found to be 2 using both differential and integral methods. According to the differential method, the reaction orders with respect to epoxide and carboxylic acid groups were calculated to be 1.2 and 0.8, respectively. The reactions could be considered as first‐order reactions with respect to each group based on integral method analysis. The activation energies and frequency factors of these esterification reactions were found to be 77.2 kJ·mol⁻¹ and 1.72E+10 L·mol⁻¹_·min⁻¹ in the presence of TPP and 65.3 kJ·mol⁻¹ and 1.44E+7 L·mol⁻¹·min⁻¹ in the presence of TEA. The thermodynamic parameters of reaction in the presence of TPP and TEA were calculated. The results confirmed that both reactions were spontaneous and irreversible. It was found that the reaction in the presence of TEA produced a highly ordered activated complex.     

Aluminum sulphate hydrates

Three different calculation methods of deriving kinetic parameters (activation energy and preexponential factor) from dynamic TG data have been applied for the sulphate decomposition stage of the aluminum sulphate octadecahydrate. The constant rate experiments were carried out by Derivatograph and DuPont thermobalances. The three parameters estimation methods included a simple differential method, the classical Coats-Redfern and a new direct integral method. The fits of the curves obtained by these procedures were compared both graphically and numerically. It was found that the direct integral method gave the most satisfactory results. With the order type reaction models this method in each case produced the smallest residual deviation values and the best fitting curves compared to those obtained by the other two methods. The activation parameters calculated by the differential method were not acceptable at all, for the estimated curves were very far from the measured ones.     

A comparison of direct methods to determine n-th order kinetic parameters of solid thermal decomposition for use in fire models

Pyrolysis models for burning solids in fire simulations are sensitive to the values of the activation energy, frequency factor, and reaction order that characterize the thermal decomposition of the solid to gaseous fuel, so direct measurement of these kinetic parameters is recommended, and simple methods are preferred. Three direct methods were evaluated with regard to the ability of their kinetic parameters to reproduce the thermal decomposition of five polymers measured by differential thermogravimetric analysis using the reaction order model. It was found that the two multiple heating rate methods produced identical, physically based kinetic parameters, while the peak property method produced non-physical kinetic parameters. However, all of these kinetic parameters in a single-step reaction order model gave reasonably good conversion histories for non-charring and moderately charring polymers. For a highly charring polymer, the conversion histories were poorly described without a multiple step reaction. The temperature at the maximum rate of conversion was found to be essentially independent of the reaction order, which decouples the frequency factor from the reaction order in the direct kinetic methods. Any of the direct methods are sufficiently accurate to obtain kinetic parameters for pyrolysis models because of the inherent spatial and temporal averaging of reaction rates at the burning surface of a thick solid and the uncertainty in the heat transfer mechanisms and thermo-physical parameters used in the models.     

对氯苯甲酸铕与邻菲咯啉络合物热分解动力学参数及寿命的测定

用TG-DTG技术研究了对氯苯甲酸铕与邻菲咯啉络合物在静态空气中的热分解,用Coats-Redfern(CR)法、Horowitz-Metzger(HM)法、Madhusudanan-Krishnan-NInan(MKN)法、Ozawa法和Kissinger法计算了对氯苯甲酸铕与邻菲咯啉络合物第一步热分解反应的动力学参数活化能（E）、指前因子（A）、反应级数（n)等。用等温TG法得到失重10%的E、A值和寿命方程：lnτ=-23.0189 17974.1/T。     

Mechanism and reaction rate of the karl-fischer titration reaction: Part III. Rotating ring-disk electrode measurements— comparison with the aqueous system

A platinum disk-platinum ring electrode was used to investigate the oxidation of sulfur dioxide by iodine and triiodide in aqueous solutions. Contrary to methanolic solutions, where the monomethyl sulfite ion is the only oxidizable species, in aqueous solutions both the hydrogen sulfite ion and the sulfite ion can be oxidized. The reaction rate was generally so high, that the method for measurements of homogeneous second order reactions had to be used. At pH values >5, the reaction proceeded too fast to be measured reliably. In a solution “diluted” with ethanol (50% of weight), however, the reaction rate was within the range where a rotating ring-disk electrode can be applied to measure fast homogeneous reactions. At very low pH values both the first order calculation technique and the second order method could be used. The results with both methods were in fair agreement.     

A combined explicit-implicit method for high accuracy reaction path integration

We present the use of an optimal combined explicit-implicit method for following the reaction path to high accuracy. This is in contrast to most purely implicit reaction path integration algorithms, which are only efficient on stiff ordinary differential equations. The defining equation for the reaction path is considered to be stiff, however, we show here that the reaction path is not uniformly stiff and instead is only stiff near stationary points. The optimal algorithm developed in this work is a combination of explicit and implicit methods with a simple criterion to switch between the two. Using three different chemical reactions, we combine and compare three different integration methods: the implicit trapezoidal method, an explicit stabilized third order algorithm implemented in the code DUMKA3 and the traditional explicit fourth order Runge-Kutta method written in the code RKSUITE. The results for high accuracy show that when the implicit trapezoidal method is combined with either explicit method the number of energy and gradient calculations can potentially be reduced by almost a half compared with integrating either method alone. Finally, to explain the improvements of the combined method we expand on the concepts of stability and stiffness and relate them to the efficiency of integration methods.     

聚苯并双噁唑酰亚胺的热分解动力学研究

采用二步法合成了以2,6-二(对-氨基苯)苯[1,2-d;5,4-d’]二噁唑和1,4-二(3,4-二苯氧基)苯四甲酸二酐(HQDPA)为单体的聚苯并双噁唑酰亚胺.该聚酰亚胺的预聚体聚酰胺酸的黏度为1.70 dL/g,经过热环化后能够生成浅黄色的聚酰亚胺薄膜.通过热重分析法研究了聚苯并双噁唑酰亚胺在N2气氛中的热降解机理.采用Flynn-Wall-Ozawa和Friedman法计算了聚苯并双噁唑酰亚胺热降解表观活化能,分别为356.36kJ/mol和370.54 kJ/mol,平均值为363.45 kJ/mol;反应级数为4.22,指前因子为6.44×1016s-1.采用Coast-Redfern法和Phadnis-Deshpande法研究了聚苯并双噁唑酰亚胺的热降解固相反应机理,认为该聚酰亚胺的热降解机理属于反曲线(A3)机理,是成核和增长模式(Avrami equation 2方程)控制的热降解反应,积分形式为g(X)=[-ln(1-X)]3.     

丝氨酸热分解机理的研究

用热重法(TG)、差热分析(DTA)和红外光谱(IR)方法测试了丝氨酸的热分解过程,用量子化学方法在RHF/6-21G水平上全优化计算了丝氨酸及其热分解中间产物、产物分子的几何构型,得到其总能量和Mulliken集居数等数据.从理论上证明了环氧中间产物的存在.通过对实验结果和计算结果如Mulliken集居数的分析,提出了丝氨酸的热分解反应机理是先失去CO2为主要反应通道,同时伴有先失去NH3而生成环氧中间产物的副反应发生.     

多元校正-速差动力学分光光度法同时测定三组分有机磷农药

速差动力学分析结合化学计量学对动力学数据进行解析计算, 可扩大动力学分析的范围, 提高分析的准确度. 本文利用对硫磷、甲基对硫磷和杀螟硫磷在碱性介质中能与氧化剂过氧化氢发生氧化反应生成对硝基苯酚的性质, 引入多元校正方法中的经典最小二乘法(CLS)、偏最小二乘法(PLS)和主成分回归法(PCR)对动力学数据进行解析, 实现了三组分人工合成样品的同时测定.     

用分光光度法测量碳酰肼及孔雀石绿与碳酰肼的缩合反应动力学

用分光光度法研究了(15.0～22.0) ℃温度区间，水溶液中孔雀石绿和碳酰肼的缩合反应动力学。结果表明：此反应为二级反应，对于反应物分别为一级反应，离子强度在(0.2～1.0) mol·L^-1内对该反应产生负盐效应。提出了孔雀石绿和碳酰肼的反应机理。据此机理导出的速率方程与实验结果相吻合。在此基础上提出了测量碳酰肼浓度范围在(0.02～0.5)×10^-3 mol·L^-1的分光光度法。     

Electrophoretically mediated reaction of glycosidases at a nanoliter scale

We have investigated electrophoretically mediated microanalysis (EMMA) for the assay of a native glyco-enzyme. As a representative of this class of enzyme, beta-glucosidase was selected, and the reaction was analyzed. Our EMMA was based on the plug-plug interaction of enzyme and substrate plugs, which is essential to reduce quantities of materials. Furthermore, we have addressed the problem of incompatibility of the enzymatic reaction and separation of the reactants. As a result, EMMA of native glycosidase was achieved with a reaction volume of approximately 20 nL and the Michaelis constant was estimated according to the Lineweaver-Burk plot. The current method may have advantages over traditional assay methods, especially in terms of the amount of enzyme (ng order) and substrate (pmol order) required for a reaction.     

Novel phase-fitted symmetric splitting methods for chemical oscillators

Splitting strategy is considered for the numerical solution of oscillatory chemical reaction systems. When applied to the harmonic oscillator, traditional splitting methods with constant coefficients are shown to be have some order of phase lag though they are zero-dissipative. Phase-fitted symmetric splitting methods of order two and order four are constructed. The result of the numerical experiment on the Lotka–Volterra system shows that the new phase-fitted symmetric splitting methods are more effective than their prototype splitting methods and can preserve the invariant of the system in long-term compared with the classical Runge–Kutta method.     

A simple method for analysis of consecutive reactions with a second order formation and a first order decay of an intermediate

A simple method is developed to evaluate rate constants from absorbance-time traces for a pair of consecutive reactions consisting of a second order formation and a first order decay of an intermediate. Initially, a first order profile is simulated utilizing the data near the end of the reaction. The difference between this simulated and observed profiles provides the absorbance-time data for the initial phase from which a second order rate constant is evaluated. These rate constants were used to simulate composite kinetic curves which were then compared with experimental curves. This method was used to test the reaction between cis-Pt(NH₃)₂(H₂O)₂ ²⁺ and a nonapeptide, ERFKCPCPT. The reaction proceeds through a cysteine coordinated intermediate formed in a second order process (first order with respect to each reactant). The intermediate is then converted to a product through a first order process, in which both cysteines are coordinated to platinum(II).     

Per-O-methylation reaction for structural analysis of carbohydrates by mass spectrometry

Per-O-methylation of carbohydrates is an important sample preparation step in structural analysis of complex carbohydrates, which has generated considerable interest as shown by thousands of citations in the last 10 years. This article provides a critical overview of the per-O-methylation methods applied for structural analysis of carbohydrates by mass spectrometry. The understanding of the O-methylation mechanism can help the researchers to apply the adequate O-methylation method and can generate new ideas in the effort of improving this reaction. The per-O-methylation of carbohydrates is relied upon stepwise reactions. The parameters that affect the reaction are discussed for the most important methods and are critically commented for each reaction step. The limits of each method are emphasized. The improvements of the per-O-methylation reaction are described in detail with their advantages and disadvantages and some illustrative examples are given. The methods that give complete O-methylation in non-hazardous conditions with high yields within minutes at room temperature with a very low amount of side-products are especially highlighted.     

L-缬氨酸旋光异构的两种光反应可能途径

利用密度泛函理论(DFT)和从头算分子轨道理论对L-缬氨酸的旋光异构光反应机理进行了研究. 分别用B3LYP和MP2方法在6-311++G(d, p)基组级别上全优化得到了S₀和T₁态反应路径上的反应物、产物、中间体以及过渡态结构的几何构型, 给出了反应能垒, 利用含时密度泛函理论(TD-DFT)中的B3LYP/6-311++G(d, p)方法优化得到了S₁态反应路径上的平衡态几何构型. 通过分析反应途径上各个驻点的几何构型特征, 确定了L-缬氨酸在激发态可能通过手性碳上的氢原子以羰基氧或氨基氮为中转媒介发生质子迁移来完成旋光异构反应. 进一步用自洽反应场理论中的极化连续模型(PCM)方法探讨了溶剂化效应对旋光异构反应机理的影响.     

Kinetics and Mechanism of the Ferrate Oxidation of Thiosulfate and Other Sulfur-Containing Species

The kinetics of the reaction of ferrate, FeO(4)(2-), with several sulfur-containing species in aqueous media have been investigated, and the results are reported. It was found that, when the reductant is in excess, ferrate rapidly oxidizes thiosulfate to sulfite, benzenesulfinate to benzenesulfonate, methionine to its corresponding sulfoxide, and dimethyl sulfoxide to dimethyl sulfone. The rate law for each reaction is first order with respect to each reactant and first order with respect to the hydrogen ion concentration. A mechanism for each oxidation reaction is discussed.     

Highly sensitive and selective spectrophotometric and spectrofluorimetric methods for the determination of ropinirole hydrochloride in tablets

Three sensitive, selective, accurate spectrophotometric and spectrofluorimetric methods have been developed for the determination of ropinirole hydrochloride in tablets. The first method was based on measuring the absorbance of drug solution in methanol at 250 nm. The Beer's law was obeyed in the concentration range 2.5-24 microg ml(-1). The second method was based on the charge transfer reaction of drug, as n-electron donor with 7,7,8,8-tetracyanoquinodimethane (TCNQ), as pi-acceptor in acetonitrile to give radical anions that are measured at 842 nm. The Beer's law was obeyed in the concentration range 0.6-8 microg ml(-1). The third method was based on derivatization reaction with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in borate buffer of pH 8.5 followed by measuring the fluorescence intensity at 525 nm with excitation at 464 nm in chloroform. Beer's law was obeyed in the concentration range 0.01-1.3 microg ml(-1). The derivatization reaction product of drug with NBD-Cl was characterized by IR, 1H NMR and mass spectroscopy. The developed methods were validated. The following analytical parameters were investigated: the molar absorptivity (epsilon), limit of detection (LOD, microg ml(-1)) and limit of quantitation (LOQ, microg ml(-1)), precision, accuracy, recovery, and Sandell's sensitivity. Selectivity was validated by subjecting stock solution of ropinirole to acidic, basic, oxidative, and thermal degradation. No interference was observed from common excipients present in formulations. The proposed methods were successfully applied for determination of drug in tablets. The results of these proposed methods were compared with each other statistically.     

Comparison of Chemometric and Chromatographic Methods to Obtain Kinetic Parameters for Textile Dyes during a Biodegradation Process

The concentrations of three industrial-grade textile dyes were determined in a mixture after degradation by the fungus Ganoderma sp, by using the methods of UV-Vis spectrophotometry associated with Partial Least Squares regression and HPLC and comparing the results obtained from both methods. Using the concentrations calculated from the two methods, a kinetic study of the biodegradation mediated by the fungus was performed. The rate constants and the activation energies for this transformation were obtained for each dye in the mixture. The concentration of Remazol Blue R ESP could be determined by the HPLC method, and the value obtained was comparable with the result using the Partial Least Squares regression method. The Partial Least Squares regression method offers advantages over the HPLC method for the quantification of dyes in textile effluents, as it provides the kinetic parameters of the biodegradation reaction.     

A comparison of flow injection methods for sulfide determination based on phenothiazine dyes produced from diverse aromatic amines

In the present work a systematic comparison among spectrophotometric flow injection methods for sulfide determination based on phenothiazine dye production from diverse aromatic p-substituted amines were performed. The behavior of N,N-dimethylphenyl-p-diamine (DMPD), N,N-diethylphenyl-p-diamine (DEPD), phenyl-p-diamine (PPD), p-aminophenol (PAP) and other three aromatic amines was investigated and the chemical parameters of proposed flow methods were optimized by applying central composite design. For each evaluated method the concentration of amine, Fe³⁺ and H₂SO₄ was optimized and after the evaluation of reagents addition order the flow parameters were independently ascertained. Analytical signal was strongly diminished in the presence of iodide for flow methods based on the reaction of sulfide with DMPD, PPD or DEPD while fluoride was considered as an important interference for methods based on the reaction with PPD or PAP. The evaluated aromatic amines have permitted sulfide determination in a wide concentration range from 0.05 to 3.0 mg L^− 1 and limits of detection (3σ) varying from 18.8 to 51.0 μg L^− 1, for DEPD and PPD, respectively. The sensitivity of flow methods based on PPD and DMPD was higher even as PAP has permitted sulfide determination in a large sulfide concentration range. In addition, higher throughput was attained for DMPD method. The proposed methods were applied for sulfide determination in industrial wastewater and the obtained results were in agreement with reference method at 95% confidence level.