Kinetics and mechanism of the reduction of monochloramine by hydroxylamine and hydroxylammonium ion

The kinetics and mechanism by which monochloramine is reduced by hydroxylamine in aqueous solution over the pH range of 5–8 are reported. The reaction proceeds via two different mechanisms depending upon whether the hydroxylamine is protonated or unprotonated. When the hydroxylamine is protonated, the reaction stoichiometry is 1:1. The reaction stoichiometry becomes 3:1 (hydroxylamine:monochloramine) when the hydroxylamine is unprotonated. The principle products under both conditions are Cl^–, NH⁺₄, and N₂O. The rate law is given by ?[d[NH₂Cl]/dt] = k₊[NH₃OH⁺][NH₂Cl] + k₀[NH₂OH][NH₂Cl]. At an ionic strength of 1.2 M, at 25°C, and under pseudo‐first‐order conditions, k₊= (1.03 ± 0.06) ×10³ L · mol^?1 · s^?1 and k₀=91 ± 15 L · mol^?1 · s^?1. Isotopic studies demonstrate that both nitrogen atoms in the N₂O come from the NH₂OH/NH₃OH⁺. Activation parameters for the reaction determined at pH 5.1 and 8.0 at an ionic strength of 1.2 M were found to be ΔH? = 36 ± 3 kJ · mol^–1 and Δ S? = ?66 ± 9 J · K^?1 · mol^?1, and Δ H? = 12 ± 2 kJ · mol^?1 and Δ S? = ?168 ± 6 J · K^?1 · mol^?1, respectively, and confirm that the transition states are significantly different for the two reaction pathways. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 124–135, 2006     

The proton exchange reaction between indene and the indenyl anion

The proton exchange reaction between the indenyl carbanion and its parent compound indene has been studied by NMR as a function of temperature. The rate of this bimolecular reaction is very low and has been found to be strongly dependent on the polarity of the solvent. In solvents like dimethoxyethane (? = 7·2) and diglyme the reaction becomes manifest in the NMR spectrum only at elevated temperatures (T > 150°C). In hexamethylphosphortriamide (? = 30) the rate is much greater and line broadening may be observable at room temperature. The reaction in this solvent is characterised by a frequency factor f = 7 × 10⁷ 1 mol^?1 s^?1, an activation enthalpy ΔH ≠ = 9·5 kcal mol^?1 and an entropy of activation ΔS≠ = ?23 e.u. The low reaction rate and its solvent dependence are briefly discussed.     

Structure and stability of the HFF and FHF radicals

The structure and stability of the HFF and FHF isomers in their two lowest electronic states is studied by means of ab initio SCF and CI calculations employing a double-zeta basis plus various polarization functions. Both complexes can be essentially described by an HF dipole (exhibiting a standard HF bond length) attracting a fluorine atom, with an FF distance of 5.14 bohr calculated for the HF··F ground state and an H··F bond of 4.3 bohr for the most stable FHF species. The HF₂ radical is found to prefer a bent structure in its ²Σ⁺ - ²A' ground state with an extremely flat potential curve, while the first very low-lying excited state of HF₂ as well as both components of the ground (in this case ²Π) state of the FH··F complex are calculated to be linear. The symmetric FHF structure exhibits optimal bond lengths at approximately 2.1 bohr but is considerably less stable than the asymmetrical arrangement of nuclei. With respect to dissociation into HF + F the HF₂ form is found to be stable in both (²Σ⁺ - A') and ²Π states while the conformer FH··F shows a minimum only for the ²Π ground state; the exothermicity of the H + F₂ → HF + F reaction is calculated to be 104.6 kcal mol^?1 in good agreement with the experimental quantity of 102.5 ± 2.8 kcal mol^?1. Comparison with the negative ions HF₂^?and FHF^? is made whenever appropriate.     

Thermal Behavior of 2‐(Dinitromethylene)‐1,3‐diazacyclopentane

A new compound, 2‐(dinitromethylene)‐1,3‐diazacyclopentane (DNDZ), was prepared by the reaction of 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) with 1,2‐diaminoethane in N‐methylpyrrolidone (NMP). Thermal decomposition of DNDZ was studied under non‐isothermal conditions by DSC, TG/DTG methods, and the enthalpy, apparent activation energy and pre‐exponential factor of the exothermic decomposition reaction were obtained as 317.13 kJ·mol^?1, 269.7 kJ·mol^?1 and 10^24.51 s^?1, respectively. The critical temperature of thermal explosion was 261.04°C. Specific heat capacity of DNDZ was determined with a micro‐DSC method and a theoretical calculation method, and the molar heat capacity was 205.41 J·mol^?1·K^?1 at 298.15 K. Adiabatic time‐to‐explosion was calculated to be a certain value between 263–289 s. DNDZ has higher thermal stability than FOX‐7.     

Determination of salutary parameters to facilitate bio-energy production from three uncommon biomasses using thermogravimetric analysis

Fuels derived from biomass are renewable as well as environment friendly. In this study, three biomasses viz. husk of areca nut (Areca catheu), trunks of moj (Albizzia lucida), and bon bogori (Ziziphus rugosus) available in North-East region of India were tested as potential biofuel sources. The accentuation of this study was to determine the kinetic parameters using thermogravimetric (TG) technique under air and nitrogen atmosphere. The experiments were carried out within temperature range 300–973 K under air and nitrogen atmosphere at four different heating rates viz. 5, 10, 15, and 20 K min^?1, respectively. The mass losses at different lumps in the TG graphs were estimated. The first-order kinetic parameters such as activation energy and pre-exponential factor were calculated for different reaction zones for all the three biomass samples. Effects of atmosphere on combustion characteristics (e.g., peak temperature, ignition temperature, and reactivity index) of biomasses were also determined in this study. Areca nut husk has highest ignition temperature (526.38 K) and reactivity index (0.21) but moj has highest peak temperature (597.91 K) along with highest activation energy (348.04 kJ mol^?1) and pre-exponential factor (1.12 × 10²⁴ min^?1), respectively.     

Non-isothermal Decomposition Kinetics, Specific Heat Capac-ity and Adiabatic Time-to-explosion of a High Energy Material: 4,6-Bis(5-amino-3-nitro-1,2,4-triazol-1-yl)-5-nitropyrimidine

The thermal behavior of 4,6‐bis‐(5‐amino‐3‐nitro‐1,2,4‐triazol‐1‐yl)‐5‐nitropyrimidine (BANTNP) was studied under a non‐isothermal condition by DSC, PDSC and TG/DTG methods. The kinetic parameters (E_a and A) of the exothermic decomposition reaction are 304.52 kJ·mol^?1 and 10^24.47 s^?1 at 0.1 MPa, 272.52 kJ·mol^?1 and 10^21.76 s^?1 at 5.0 MPa, respectively. The kinetic equation at 0.1 MPa can be expressed as: dα/dT=10^25.3(1?α)^3/4exp(?3.8044×10⁴/T)/β The critical temperature of thermal explosion is 588.28 K. The specific heat capacity of BANTNP was determined with a Micro‐DSC method, and the standard molar specific heat capacity is 397.54 J·mol^?1·K^?1 at 298.15 K. The adiabatic time‐to‐explosion of BANTNP was calculated to be 11.75 s.     

Determination of the acid dissociation constants of p-benzohydroquinone by the INDO method

The stepwise acid dissociation constants for p-benzohydroquinone (QH₂) in aqueous media have been explicitly calculated for the first time, with the INDO parametrized SCF –MO method. We have optimized the geometries of QH₂, QH^?, and Q^2? and of the QH₂ · 6H₂O, QH^? · (H₃O⁺) · 5H₂O, and Q^2? · (H₃O⁺)₂ · 4H₂O systems that model the solvated species. The presence of the associated water molecules (and hydronium ions) account for the stabilization due to hydrogen bonding as well as for a part of the effect of interaction of these molecules with the respective reaction fields in an aqueous medium. To simulate the first solvation shell in a more complete manner, four more water molecules have been considered to be placed above and below the quinonoid ring and the optimized geometries of the resulting hydrated species, QH₂ · 10H₂O, QH^? · (H₃O⁺) · 9H₂O, and QH^? · (H₃O⁺) · 8H₂O, have been determined. The standard free-energy changes calculated for the dissociation of QH₂ into QH^? and H⁺ is 0.0251 Hartree (65.9 kJ mol^?1) and that of QH^? into Q^2? and H⁺ is 0.0285 Hartree (74.8 kJ mol^?1). Experimentally observed dissociation constants for these two steps correspond to free-energy changes of 0.0214 Hartree (56.2 kJ mol^?1) and 0.0248 Hartree (65.1 kJ mol^?1), respectively. © 1995 John Wiley & Sons, Inc.     

水合烟酸铜Cu(Nic)2•H2O(s)(Nic＝烟酸)的合成、表征及热力学性质

近几十年来,烟酸盐类化合物或配合物由于优越的吸收率高和无毒副作用等特点使其在化妆品、药品和食品等领域作为营养添加剂具有重要应用前景。然而,这类化合物的基础热力学数据极其缺乏,从而限制了这类化合物的理论研究和应用开发的深入开展。为此,本论文利用室温固相合成方法和球磨技术合成了一种新化合物Cu(Nic)2•H2O(s),利用化学分析、元素分析、FTIR和X-射线粉末衍射技术表征了它的结构和组成,利用精密自动绝热热量计准确地测量了它在78-400 K温区的摩尔热容。在热容曲线的T ＝ 326-346 K温区观察到一个明显的固-液相变过程。利用相变温区三次重复实验热容的测量结果确定了此相变过程的峰温、相变焓和相变熵分别为：Tfus＝(341.290 ±0.873) K, DfusHm＝(13.582±0.012) kJ×mol-1, DfusSm＝(39.797±0.067) J×K-1×mol-1。通过最小二乘法将相变前和相变后的热容实验值分别拟合成了热容对温度的两个多项式方程。通过热容多项式方程的数值积分,得到了这个化合物的舒平热容值和相对于298.15 K的各种热力学函数值,并且将每隔5 K的热力学函数值列成了表格。     

Thermal studies and spectral characterization of the chelate of bis-(η5-cyclopentadienyl titanium(IV) with salicylidene-4-methylaniline

A new chelate (η⁵-C₅H₅)₂Ti(SB)₂, whereSB=O, N donor Schiff base salicylidene-4-methylaniline, was synthesized. The course of thermal degradation of the chelate was studied by thermogravimetric (TG) and differential thermal analysis (DTA) under dynamic conditions of temperature. The order of the thermal decomposition reaction and energy of activation was calculated from TG curve while from DTA curve the change in enthalpy was calculated. Evaluation of the kinetic parameters was performed by Coats-Redfern as well as Piloyan-Novikova methods which gaven=1, ΔH=1.114 kJ·mol^?1, ΔE=27.01 kJ·mol^?1, ΔS=?340.12 kJ·mol^?1·K^?1 andn=1, ΔH=1.114 kJ·mol^?1, ΔE=20.01 kJ·mol^?1, ΔS=?342.60 kJ·mol^?1·K^?1, respectively. The chelate was also characterized on the basis of different spectral studies viz. conductance, molecular weight, IR, UV-visible and¹H NMR, which enabled to propose an octahedral structure to the chelate.     

Reaction of photogenerated fluorine atoms with dopant molecules in solid argon

The products of reactions of dopant CH₄ molecules with F atoms diffusing in solid argon at 20–30 K were identified by ESR and FTIR spectroscopy. The F atoms stabilized in the matrix were generated by UV photolysis of Ar?CH₄(CD₄)?F (1000∶1∶1) samples at 13 K. Subsequent heating above 20 K results in thawing off diffusion of the F atoms and formation of products of their reaction with CH₄: radical-molecular complexes^·CH₃?HF (^·CD₃?DF) and radicals^·CH₃ (^·CD₃). The ESR spectra of the radicala are similar to those observed for matrix-isolated^·CH₃. The^·CH₃?HF complexes are characterized by the IR band of HF stetching vibration at 3764 cm^?1. Two additional splittings on the H (a _H·=2 G) and F(a _F=16G) nuclei of the HF molecule appeal in the ESR spectrum of the complex. The latter splitting is retained in the^·CD₃?DF complex, whereA _D· <0.3G The rate constant of the reaction CH₄+F→^·CH₃+HF is equal to ?10^?25 cm³s^?1 at 20 K. Its activation energy (1.7±0.2 kcal mol^?1) is ?0.5 kcal mol^?1 greater than that in the gas phase. The collinear C_3v-configuration of the^·CH₃?HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by the comparison of the exprrimental constants of hyperfine coupling with the results of the quantum-chemical calculation.     

Radical Polymerization of N,N″-Methylenebisacrylamide by Peroxidiphosphate-Ag+ Redox System: A Kinetic Study

Abstract

The kinetics of aqueous polymerization of N,N′-methylenebisacrylamide (N,N′ -MBA) was studied under an inert atmosphere within the 20-40°C temperature range. The rate of polymerization was found to be proportional to N,N′ -MBA and square-root dependent to the concentration of Ag⁺ and peroxidiphosphate. An intramolecular cyclization prior to propagation is proposed in the mechanism to explain the kinetic data. The overall energy of activation has been found to be 30.2 ± 0.1 kJ · mol^?1. On the basis of experimental results, a suitable scheme has been proposed and a rate expression has been derived.     

Ab initio study on the mechanism of reaction HNCO+NH2

Ab initio UMP2 and UQCISD(T) calculations, with 6-311G** basis sets, were performed for the titled reactions. The results show that the reactions have two product channels: NH₂+ HNCO?NH₃+NCO (1) and NH₂+HNCO?N₂H₃+CO (2), where reaction (1) is a hydrogen abstraction reaction via an H-bonded complex (HBC), lowering the energy by 32.48 kJ/mol relative to reactants. The calculated QCISD(T)//MP2(full) energy barrier is 29.04 kJ/mol, which is in excellent accordance with the experimental value of 29.09 kJ/mol. In the range of reaction temperature 2300–2700 K, transition theory rate constant for reaction (1) is 1.68×10¹¹–3.29×10¹¹ mL·mol^-1·s^-1, which is close to the experimental one of 5.0×10¹¹mL·mol^-1·s^-1or less. However, reaction (2) is a stepwise reaction proceeding via two orientation modes,cis andtrans, and the energy barriers for the rate-control step at our best calculations are 92.79 kJ/mol (forcis-mode) and 147.43 kJ/mol (fortrans-mode), respectively, which is much higher than reaction (1). So reaction (1) is the main channel for the titled reaction.     

Equilibrium sublimation and thermodynamic properties of SnSe and SnSe2

Knudsen effusion studies of the sublimation of polycrystalline SnSe and SnSe₂, prepared by annealing and chemical vapor transport reactions, respectively, have been carried out using vacuum microbalance techniques in the temperature ranges 736–967 K and 608–760 K, respectively. From experimental mass-loss data for the sublimation reaction SnSe(s) = SnSe(g), the recommended values for the heat of formation and absolute entropy of SnSe(s) were calculated to be ΔH°_298,f = ?86.4 ± 9.9 kJ · mol^?1 and S°₂₉₈ = 89.0 ± 7.1 J · K^?1 · mol^?1. From mass-loss data for the decomposition reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SnSe}_{\rm 2} ({\rm s)} = {\rm SnSe(s)} + \frac{1}{{\rm x}}{\rm Se}_{\rm x} ({\rm g) (x} = 2 - 8) $\end{document}, the recommended values for the heat of formation and absolute entropy of SnSe₂(s) were determined to be ΔH°_298,f = ?118.1 ± 15.1 kJ · mol^?1 and S°₂₉₈ = 111.8 ± 11.8 J · K^?1 mol^?1.     

Kinetic Study on the Exothermic First-stage Decomposition Reaction of 2,4,8,10-Tetranitro-2,4,8,10-tetraaza- spiro[5,5]undecane-3,9-dione

Introduction 2,4,8,10-Tetranitro-2,4,8,10-tetraazaspiro[5,5]udecane- 3,9-dione is a typical cyclourea nitramine (Figure 1). Its crystal density is 1.91 gcm-3. The detonation velocity according to =1.90 gcm-3 is about 8670 ms-1. Its sensitivity to impact is better than that of cyclotrimethy- lenetrinitramine. So it is the potential high explosive. Its preparation,1-3 properties,1-3 hydrolytic behavior4 and electronic structure3 have been reported. In the present work, we report its kinetic pa…     

Thermal Behavior of N,N＇Bis[N-（2,2,2-trinitroethyl）-N-nitro]ethylenediamine

The thermal behavior and kinetic parameters of the exothermic decomposition reaction of N‐N‐bis[N‐(2,2,2‐tri‐nitroethyl)‐N‐nitro]ethylenediamine in a temperature‐programmed mode have been investigated by means of differential scanning calorimetry (DSC). The results show that kinetic model function in differential form, apparent activation energy E_a and pre‐exponential factor A of this reaction are 3(1 ‐α)^2/3, 203.67 kJ·mol^?1 and 10^20.61s^?1, respectively. The critical temperature of thermal explosion of the compound is 182.2 °C. The values of ΔS^≠ ΔH^≠ and ΔG^≠ of this reaction are 143.3 J·mol^?1·K^?1, 199.5 kJ·mol^?1 and 135.5 kJ·mol^?1, respectively.     

The thermal decomposition of (NH4)4V2O11 in a nitrogen atmosphere and the kinetics of the first decomposition step

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min^?1 ammonium peroxo vanadate, (NH₄)₄V₂O₁₁, decomposes to (NH₄)[VO (O₂)₂ (NH₃)] (above 93°C); this in turn decomposes to (NH₄) [VO₃ (NH₃)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol^?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol^?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.     

Study of the Interaction between a Water-soluble Cationic Fluorescent Conjugated Polymer and Bovine Serum Albumin

The interaction between a water-soluble cationic fluorescent conjugated polymer (WCFP) and bovine serum albumin (BSA) was studied using UV?CVis absorption, fluorescence and circular dichroism spectroscopies. The results show that the fluorescence of BSA is strongly quenched by the WCFP under physiological conditions (pH?=?7.4). The quenching mechanism was found to be static, which was confirmed by the quenching rate constant (Kq) and UV?CVis absorption spectra. The thermodynamic parameters (?H ^??, ?S ^?? and ?G ^??) calculated from the complexation constant, determined according to Lineweaver?CBurk equations are 38.6?kJ·mol^?1, 228?J·mol^?1·K^?1 and ?29.4?kJ·mol^?1 at 298?K. The principal interaction was proposed to be electrostatic.     

2-氯-N,N-二甲基尼古丁酰胺的热容和热力学性质研究

Low-temperature heat capacities of 2-chloro-N,N-dimethylnicotinamide were precisely measured with a high-precision automated adiabatic calorimeter over the temperature range from 82 K to 380 K. The compound was observed to melt at （342.15±0.04） K. The molar enthalpy AfusionHm, and entropy of fusion, △fusionSm, as well as the chemical purity of the compound were determined to be （21387±7） J·mol^-1, （62.51±0.01） J·mol^-1·K^-1, （0.9946±0.0005） mass fraction, respectively. The extrapolated melting temperature for the pure compound obtained from fractional melting experiments was （342.25±0.024） K. The thermodynamic function data relative to the reference temperature 298.15 K were calculated based on the heat capacity measurements in the temperature range from 82 to 325 K. The thermal behavior of the compound was also investigated by different scanning calorimetry.     

Kinetics and mechanism of the inner-sphere reduction of hexachloroplatinate(IV) by dithionite in acetate buffer

The kinetics of reduction of hexachloroplatinate(IV) by dithionite have been examined spectrophotometrically in sodium acetate?Cacetic acid buffer medium in the temperature range 288?C303?K. The reaction is first order in both platinum(IV) species and dithionite. H⁺ ion has an inhibiting effect on the rate in the pH range 3.68?C4.80. The pseudo-first order rate constant increased upon increasing both ionic strength and dielectric constant. The suggested mechanism involves an initial transition state between two like charged ions, which then decomposes to give SO₃ ^2? through the intermediate formation of free radicals. The presence of free radicals was confirmed by performing the reaction in the presence of acrylamide. PtCl₆ ^2? is finally reduced to PtCl₄ ^2?, as confirmed by thermogravimetric analysis and IR spectrophotometry. The values of ?H^?? and ?S^?? associated with the rate-determining step have been calculated as 33?±?4?kJ?mol^?1 and ?141?±?7?JK?mol^?1, respectively. The values of ?H° and ?S° for the dissociation of HS₂O₄ ^? are 16?±?4?kJ?mol^?1 and ?14?±?7?JK?mol^?1, respectively.     

Chemical equilibria 6. Measurement of equilibrium constants for the dehydrogenation of 2-methylpropan-1-ol by a vapour-flow technique

Equilibrium constants for 2-methylpropan-1-ol + 2-methylpropanal + hydrogen have been calculated from measurements of the composition of mixtures formed by passing the vapour over a catalyst at several temperatures in the range 473 to 563 K. Equations relating the changes in enthalpy and entropy of the dehydrogenation reaction to temperature were derived from the equilibrium constants with the aid of heat capacities. By coupling these changes with other thermodynamic data, the standard enthalpy of formation and the standard entropy of 2-methylpropanal at 298.15 K were calculated to be ?(215.7 ± 1.3) kJ mol^?1 and (331.2 ± 1.7) J K^?1 mol^?1 respectively, in the gas state, and ?(247.3 ± 1.8) kJ mol^?1 and (238.3 ± 4.4) J K^?1 mol^?1 respectively, in the liquid state.