Nonisothermal Kinetics of Dehydration Process of [Sm（m-CIBA）3phen]2·2H2O and [Sm（p-CIBA）3phen]2·2H2O

Compounds [Sm（m-CIBA）3phen]2.2H20 and [Sm（p-CIBA）3phen]2·2H20（m-CIBA=m-chlorobenzoate, pClBA=p-chlorobenzoate, phen=l,10-phenanthroline） were prepared. The dehydration processes and kinetics of these compounds were studied from the analysis of the DSC curves using a method of processing the data of thermal analysis kinetics. The Arrhenius equation for the dehydration process can be expressed as lnk=-38.65-243.90×l0^3/RT for [Sm（m-CIBA）3phen]2·2H2O, and lnk=38.70-172.22×103/RT for [Sm（p-CIBA）3phen]2·2H2O. The values of △H^1, △G^1, and △S^1 of dehydration reaction for the title comnonnds are determined respectively.     

Thermodynamic parameters ΔΔH and ΔΔS as probes for the transition state in the reaction of N-phenyltriazolinedione with alkenes in nucleophilic solvents

The thermodynamic parameters, ΔΔH^# and ΔΔS^#, were determined for the interception of an intermediate, with the structural characteristics of an aziridinium imide, by nucleophilic solvents during the reaction of 2-methyl-2-butene with N-phenyltriazolinedione. The experimentally measured parameters were found to be in favor of an S_N2-‘like’ transition state and showed strong dependence on the bulkiness of the incoming molecule of the nucleophile-solvent.     

Kinetics of oxidation of cysteine and captopril via Cs3[Mo(CN)8] and Cs3[W(CN)8]

The kinetics of the oxidation of cysteine and captopril via octacyanomolybdate(V) and octacyanotungstate(V) in a buffered acidic media (pH range 2.20–4.80) have been studied spectrophotometrically. The rate law for the oxidation is: Rate = k [RSH] [Ox] [H⁺]⁻¹, where RSH is cysteine or captopril and Ox is Cs₃[Mo(CN)₈] or Cs₃[W(CN)₈]. The activation parameters (E_a, ΔH^#, ΔG^#, ΔS^#) for the oxidation of cysteine and captopril via Cs₃[Mo(CN)₈] or Cs₃[W(CN)₈] have been determined. The results indicate that Cs₃[Mo(CN)₈] is more reactive than Cs₃[W(CN)₈] as an oxidizing agent. Effects of pH, ionic strength, temperature, dielectric constant of the reaction medium and copper(II) ions on the oxidation rate have been studied. Mechanisms for the oxidation of cysteine to cystine and captopril to the corresponding disulfide have been proposed.     

Activation parameters of supercritical and gas-phase β-pinene thermal isomerization

New data on enthalpy and entropy contributions to the energy barrier of β-pinene thermal isomerization were obtained. The rate of β-pinene conversion is higher in supercritical EtOH (P = 120 atm) than in the gas phase (P ≤ 1 atm, without solvent, or for inert carrier gas N₂) at equal temperatures. The highest activation energy E _Σ of total β-pinene conversion is also observed in reactions in the supercritical (sc) condition. Activation parameters ΔH _Σ ^# , ΔS _Σ ^# , and ΔG _Σ ^# depend strongly on the reaction pressure. Thus, at P ≤ 1 atm (gas-phase reaction) the values of ΔS _Σ ^# are negative, while at sc conditions at P = 120 atm is positive. The linear dependences lnk _Σ0 ? E _Σ and ΔS _Σ ^# ? ΔS _Σ ^# indicate an isokinetic relation (IKR) and enthalpy-entropy compensation effect (EEC). The isokinetic temperature was calculated (T _iso = 605.5 ± 22.7 K). It was shown that elevation of temperature reduces the value of ΔG _Σ ^# (T) upon sc thermolysis only, whereas in all gas-phase reactions ΔG _Σ ^# (T) increases. At equal reaction temperatures, the greatest values of K _eq ^# (T) proved to be typical for thermolysis in sc-EtOH. We hypothesize that the rate of total β-pinene conversion increases dramatically due to a considerable shift in equilibrium toward higher concentrations of activated complex y _TS ^# . A detailed analysis of activation parameters shows that the IKR and EEC coincide, evidence of a common mechanism of β-pinene conversion observed under different reaction conditions, including thermolysis in sc-EtOH.     

The densities and viscosities of aqueous solutions of glycine and glycylglycine containing carbohydrates and structural properties of the ternary systems

Apparent molar volumes, V _? for glycine (Gly) and glycylglycine (Gly-Gly) in aqueous D(+)-glucose and sucrose solutions have been determined from solution density, ρ measurements at 298.15, 303.15, 308.15, and 313.15 K as a function of the concentration of solutes (Gly and Gly-Gly). The standard partial molar volume, V _? ⁰ , transfer volume, ΔV _?(tr) ⁰ , for Gly and Gly-Gly from water to aqueous carbohydrate solutions, partial molar expansibility, E _? ⁰ , and hydration number, n _H of solute have been calculated. The viscosity data have been analyzed by means of Jones-Dole equation to obtain A- and B-coefficients, free energy of activation of viscous flow per mole of solvent, Δμ ₁ ^0# , and solute, Δμ ₂ ^0# , enthalpy, ΔH ^0#, and entropy of activation, ΔS ^0# of viscous flow were evaluated. The behavior of these parameters has been interpreted in terms of solute-solute and solute-solvent interactions.     

Thermal and spectral studies of 5-(phenylazo)-2-thiohydantoin and 5-(2- hydroxyphenylazo)-2-thiohydantoin complexes of cobalt(II), nickel(II) and copper(II)

Complexes of 5-(phenylazo)-2-thiohydantoin (L¹) and 5-(2-hydroxyphenylazo)-2-thiohydantoin (HL²) with Co(II), Ni(II) and Cu(II) salts have been synthesised and characterized by elemental analysis, conductivity, magnetic susceptibility, UV-Vis, IR, ESR and TG studies. The magnetic and spectral data suggested octahedral geometry for [L¹M(OAc)₂(H₂O)₂]·xH₂O {M=Ni^ll and Cu^ll} and [L¹CuCl₂(H₂O)]·H₂O (dimeric form for the latter), trigonal bipyramidal geometry for [L²Co(OAc)(H₂O)]·2H₂O, square pyramidal geometry for [L²Ni(OAc)(H₂O)]·H₂O and square planar geometry for [L²CuCl]·2H₂O. TG studies confirmed the chemical formulations of these complexes and showed that their thermal degradation takes place in three to five steps, depending on the type of the ligand and the geometry of the complex. The kinetic parameters (n, E^#, A, ΔH^#, ΔS^# and ΔG^#) of the thermal decomposition stages were computed using the Coats-Redfern and other standard equations and are discussed.     

Kinetics and mechanism of anation of cis -diaquo- bis -oxalatochromate(III) ion byDL -alanine in ethanol-water mixtures of varying dielectric constant

The kinetics of the anation reaction of cis-diaquo-bis-oxalatochromate(III) ion by DL-alanine has been studied spectrophotometrically in the pH range 3.8 to 7.3, where DL-alanine remains in zwitterionic form. A second-order rate law has been established. Reaction rates in three different ethanol-water mixtures were measured. In each solvent medium the anation rate is higher as compared to water exchange reaction at a particular temperature. The activation parameters (gDH^# and ΔS^#) in different ethanol-water mixtures were obtained from Eyring plots. ΔG^#(ΔH^# −TΔS ^#) values were calculated in each solvent medium and compared with that of the isotopic water exchange process. A reaction mechanism involving theS _N2 path has been suggested.     

Oxa-bridged cyclophanes featuring thieno[2,3-b]thiophene and C2-symmetric binol or bis-naphthol rings: synthesis, structures, and conformational studies

Oxa-bridged cyclophanes 4/6 and 8/10 featuring thieno[2,3-b]thiophene ring and binol or bis-naphthol have been synthesized. The structures are assigned by 2D NMR data and the identity of 4 is also independently established by a single X-ray crystallography. From dynamic NMR analysis, the Arrhenius energy of activation ΔG^# for bridge inversions in 4 and 6 was calculated to be 15.3 and 12.9 kcal/mol, respectively. A higher ΔG^# for 4, relative to the ester free 6 is attributable to the steric compression stemming from C2/C5 ester substituents to the bridge inversion processes. While the methylene bridges undergo inversion in 4 and 6, the naphthyl-naphthyl pseudo-rotation appears to be restricted even at higher temperatures. This is supported by retention of the optical purity of the chiral (−) 4 under thermal condition. For the case of bis-naphthol cyclophane 8, we observed the flipping of both the -OCH₂- and the naphthyl-CH₂-naphthyl bridges with ΔG^# of ca. 11.4 kcal/mol. However, the ester free cyclophane 10 remained conformationally mobile even at −55 °C and its ΔG^# was assumed to be <11.4 kcal/mol. The presence of an extra -CH₂- linker in bis-naphthol cyclophanes 8/10 renders them relatively more conformationally mobile compared to binol cyclophanes 4/6, possessing a rigid naphthyl-naphthyl geometry.     

Ion association and solvation behavior of some alkali metal acetates in aqueous 2-butanol solutions at T = 298.15, 303.15 and 308.15 K

Molar conductance of lithium acetate, sodium acetate and potassium acetate were studied in aqueous 2-butanol solutions with an alcohol mass fraction (w₂) of 0.70, 0.80 and 0.90 at 298.15, 303.15 and 308.15 K. The conductance data were analyzed with the Fuoss conductance-concentration equation to evaluate the limiting molar conductances (Λ₀), association constants (K_A,c) and cosphere diameter (R) for ion-pair formation. Gibbs energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) for ion-association reaction were derived from the temperature dependence of K_A,c. Activation energy for ionic movement (ΔH^#) was derived from the temperature dependence of Λ₀. Based on the composition dependence of Walden products (Λ₀η₀) and different thermodynamic properties (ΔG⁰,ΔH⁰, ΔS⁰ and ΔH^#), the influence of the solvent composition on ion-association and solvation behavior of ions were discussed in terms of ion-solvent, ion-ion interactions and the structural changes in the mixed solvent media.     

A proton magnetic resonance study of ligand exchange on hexakis(1,1,3,3-tetramethylurea) thulium(III)

A ¹H NMR study of the rate of exchange of 1,1,3,3-tetramethylurea (tmu) on [Tm(tmu)₆]³⁺ is found to be independent of [tmu] over a five-fold variation in CD₃CN solution, and to be characterized by k(298.2 K) = 145 ± 1 s⁻¹, ΔH^# = 29.3±0.3 kJ mol⁻¹, and ΔS^# = 105±1 J K⁻¹ mol⁻¹. These data are discussed in conjunction with data from related lanthanide and pseudo-lanthanide systems and the mechanistic implications are considered.     

Electron donor-acceptor interaction of 3,4-dimethylaniline with 2,3-dicyano-1,4-naphthoquinone

The electron donor–acceptor (EDA) interaction between 2,3-dicyano-1,4-naphthoquinone (DCNQ) and 3,4-dimethylaniline (3,4-DMA) is studied in chloroform, dichloromethane and 1:1 (v/v) mixture of chloroform and dichloromethane. The rate of formation of the product was measured as a function of time using UV–vis spectrophotometer. The formation constant (K) and molar extinction coefficient (?) values for the formation of EDA complex were evaluated in the temperature range of 20–35 °C. The pseudo-first-order rate constant (k₁) and the second-order rate constant (k₂) for the disappearance of EDA complex and for the formation of product were evaluated. The activation parameters (ΔH^#, ΔS^# and ΔG^#) of the reaction were determined by temperature dependence of rate constants using the Arrhenius plots. The effect of relative permittivity of the medium on the reaction is discussed. The observed results indicate that formation of final product proceeds through initial formation of EDA complex as an intermediate. The product of the reaction was purified by column chromatography method and identified as 3-(N-3,4-dimethyl-phenylamino)-2-cyano-1,4-naphthoquinone by elemental analysis, IR and NMR spectroscopy. On the basis of kinetic, analytical and spectroscopic results, a plausible mechanism for the formation of EDA complex and its transformation into product is proposed.     

Kinetic parameters and solid state mechanism of the thermal dehydration of trans[CrF(H2O)(aa′)2]K[Cr(CN)6]H2O And trans[CrF(H2O)(aa′)2]K[CrNO(CN)5]H2O (aa′=ethylenediamine or 1,3-diaminopropane)

The solid phase thermal deaquation of trans[CrF(H₂O)(aa′)₂]K[Cr(CN)₆]H₂O and trans[CrF(H₂O)(aa′)₂]K[CrNO(CN)₅]H₂O (aa′=ethylenediamine or 1,3-diaminopropane) has been investigated by means of TG measurements. The kinetic parameters (activation energy, E_a, activation entropy, ΔS^#, and frequency factor, k₀) have been determined by comparison of the isothermal and non-isothermal studies for all the principal g(α) expressions. The values found for the activation energy are low (between 80 and 110 kJ mole^?1, approximately) and permit the assignment of the deaquation-anation mechanism of the S_N1 type, involving square-pyramid activated complex and elimination of water as Frenkel defects.     

An investigation on solid-state pyrolytic decomposition of barium trihemiaquatris(oxalato)lanthanate(III)decahydrate using TG–DTA in air and DSC in nitrogen

A heterobimetallic oxalate coordination compound, barium(II)trihemiaquatris(oxalato)lanthanate(III)decahydrate, has been synthesized and characterized by elemental analysis, IR and electronic spectral studies. Crystalline nature of the compound with orthorhombic symmetry is corroborated from powder X-ray diffraction studies. The solid-state pyrolytic decomposition studies (TG, DTG and DTA) in air showed that the compound decomposed mainly to BaO, La₂O₃ and BaLa₂O₄ along with carbides of both the metal at ca. 1,000 °C through a number of intermediate steps. The DSC studies in nitrogen up to 670 °C found that the compound crumbled through several endothermic and one exothermic processes. The kinetic parameters, E*, lnk _o, ΔH ^# and ΔS ^# of dehydration and decomposition steps in nitrogen are evaluated from DSC peaks and discussed.     

Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5–4.5) and temperature (15–35°C) in the presence and absence of surfactant were investigated. Activation parameters, ΔE _a, ΔH ^#, ΔS ^#, ΔG ^≠, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γ_max), minimum area per surfactant molecule (A _min), average area occupied by each molecule of surfactant (a), surface pressure at the CMC (Π_max), Gibb’s energy of micellization (ΔG _M°), Gibb’s energy of adsorption (ΔG _ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.     

Investigation on the reaction of iron powder mixture as a portable heat source for thermoelectric power generators

This paper reports our investigation on the thermal behavior and ignition characteristics of iron powder and mixtures of iron with other materials such as activated carbon and sodium chloride in which iron is the main ingredient used as fuel. Thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetric analysis were used to characterize the materials and for further understanding of reaction kinetics of the pyrophoric iron mixtures. The experimental results demonstrated that iron micron particles react exothermically to the oxygen in atmosphere and produced iron oxide with ignition temperature of 427.87 °C and heat generation of 4,844 J g^?1. However, in this study, the pyrophoric iron mixture acts as a heat source for the thermoelectric power generators, the final mixture composition is determined to compose of iron powder, activated carbon, and sodium chloride with the mass ratio of approximately 5/1/1. The mixture generated two exothermic peaks DSC curves that showed ignition temperature of 431.53 and 554.85 °C and with a higher heat generation of 9,366 J g^?1 at higher temperature. The effects of test pan materials and heating rate on the ignition were also examined by DSC method. Kinetic data such as the activation energy (E _a), the entropy of activation (ΔS ^# ), enthalpy of activation (ΔH ^# ), and Gibbs energy of activation (ΔG ^# ) on the ignition processes was also derived from the DSC analysis. From the ignition temperature, heat generation, and kinetics test data, the mass ratio of 5/1/1 proved to generate the most amount of heat with high temperatures for the standalone thermoelectric power generators.     

Kinetic and thermodynamic properties of the aerial oxidation of hydroquinone in developer solutions

The aerial oxidation kinetics of hydroquinone in a freshly prepared developer solution at different temperatures and pHs has been studied. The activation parameters, Ea, ΔG# , ΔS# , ΔH# and enthalpy of formation of activated complex, ΔHfo(X# ), are determined. The large negative value of free energy of activation ΔG# proves that hydroquinone extremely tends to be oxidized by air at optimum temperature (20℃) and optimum pH (10.5) and converts to the activated complex semiquinone. It was also found that if the pH of the developer solution is increased from 9.3 to 10.5 the reaction rate will increase by a factor of 2.     

Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K₂S₂O₈/Na₂S₂O₃ initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1 h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (E_a) and enthalpy (ΔH^#), entropy (ΔS^#) and free energy (ΔG^#) of activation for the adsorption process. The value of E_a for adsorption was found to be 10.84 kJ · mol^?1 and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64 · 10 mg · g^?1 at T = 303 K. The thermodynamic parameters such as changes in free energy (ΔG^°), enthalpy (ΔH^°), and entropy (ΔS^°) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. VI. Thermolyse d'azo-1,1′-(cyano-1 cyclanes) dans differents solvants

Bis-azo-cyanocyclo-pentane, -hexane and -heptane are prepared and the kinetics of their thermolysis in several solvents are studied by differential scanning microcalorimetry. Unlike activation enthalpy and entropy, activation free enthalpy does not depend on solvent. Moreover its variation with temperature is quite small in each kinetic study temperature range. Thus ΔG^# is given as an intrinsic stability characteristic of azo-nitriles. “Kinetic compensation effect” between ΔS^# and ΔH^# is discussed.     

Kinetics and mechanism of the reduction of colloidal MnO2 by glycyl-leucine in the absence and presence of surfactants

The kinetics of the reduction of water-soluble colloidal manganese dioxide by glycyl-leucine (Gly-Leu) has been investigated in the presence of perchloric acid both in aqueous as well as micellar media at 35 °C. The study was carried out as functions of [MnO₂], [Gly-Leu] and [HClO₄]. The first-order-rate is observed with respect to [MnO₂], whereas fractional-order-rates are determined in both [Gly-Leu] and [HClO₄]. Addition of sodium pyrophosphate and sodium fluoride enhanced the rate of the reaction. Further, the use of surfactant micelles is highlighted as, in favourable cases, the micelles help the redox reactions by bringing the reactants into a close proximity due to hydrogen bonding. While the ionic surfactants SDS and CTAB have not shown any effect on the reaction rate, the nonionic surfactant TX-100 has catalytic effect which is explained in terms of the mathematical model proposed by Tuncay et al. (1999). The Arrhenius and Eyring equations are valid for the reaction over the range of temperatures used and different activation parameters (E_a, ΔH^#, ΔS^# and ΔG^#) have been evaluated. Kinetic studies show that the redox reaction between MnO₂ and Gly-Leu proceeds through a mechanism combining one- and two-electron pathways: Mn(IV) → Mn(III) → Mn(II) and Mn(IV) → Mn(II). On the basis of the observed results, a possible mechanism has been proposed and discussed.