Magnetic susceptibility of FeOCl

Magnetic susceptibility (χ) measurements on FeOCl are reported. The data were obtained on single crystals over the temperature range 7–400 K. A small but distinct singularity at the Neel temperature T_N ≈ 84 K was observed; extensive short-range ordering above T_N was also evident from these data. The present work suggests that the intrinsic χ(T) of FeOCl was masked by magnetic impurities in the two previous χ studies of this compound.     

Kinetic studies of pyridine catalyzed alkanesulfornylation of phenols

Kinetic studies of the pyridine catalyzed reaction between phenylmethanesulfochloride and phenols in non-aqueous media have provided quantitative estimates for the effect of reactant structure, catalyst and reaction medium polarity on competing reaction routes. For the first time a sulfene mechanism in pyridine catalyzed processes of alkanesulfonyl transport has been discovered. Criteria for its realization are suggested.

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Kinetic study of the equilibrium in the methanesulfonic acid-water system

A kinetic study of the hydrolysis of ethyl isovalerate in the methanesulfonic acid-water system from pure water to 60.5% CH₃SO₃H at 25°C showed that the hydrolysis rate is directly proportional to the concentration of H₅O₂ ⁺ ions determined by IR spectroscopy. The hydrolysis mechanism is the same as in hydrochloric acid and sulfuric acid solutions. Evidence was found for correctness of the measurements of the equilibrium concentrations of molecules and ions in aqueous methanesulfonic acid solutions by multiple frustrated total internal reflection IR spectroscopy. The possibility was demonstrated for an independent measurement of the equilibrium concentrations of H₅O₂ ⁺ ions by a kinetic method in aqueous acid solutions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1694–1697, July, 1991.     

Kinetic study of chitosane/genipin system using DSC

Knowledge of the the kinetic study of chitosan/genipin allow to know the different effects that time and temperature have on the cure reaction of the material. The total enthalpy of reaction, the glass transition temperature and the partial enthalpies have been determined using DSC in dynamic mode. Two models, one based on chemical kinetics and the other accounting for diffusion were used. The incorporation of the diffusion factor in the second model allowed for the cure kinetics to be predicted the whole range of conversion.     

Kinetic resolution of sec-alcohols by a new class of pyridine catalysts having a conformation switch system

The catalysts having a conformation switch system induced by acylation and deacylation serve as asymmetric acylating catalysts of sec-alcohols. The kinetic resolution of various sec-alcohols resulted in good to excellent selectivities in the presence of 0.5 to 0.05 mol % of catalyst 1a. The conformation switch system plays a key role to attain both good selectivity and high catalytic activity.     

Kinetic study on external mass transfer in high performance liquid chromatography system

External mass transfer coefficients (k_f) were measured for a column packed with fully porous C₁₈-silica spherical particles (50.6 μm in diameter), eluted with a methanol/water mixture (70/30, v/v). The pulse response and the peak-parking methods were used. Profiles of elution peaks of alkylbenzene homologues were recorded at flow rates between 0.2 and 2.0 mL min⁻¹. Peak-parking experiments were conducted under the same conditions, to measure intraparticle and pore diffusivity, and surface diffusion coefficients. Finally, the values of k_f for these compounds at 298 K were derived from the first and second moments of the elution peaks by subtracting the contribution of intraparticle diffusion to band broadening. As a result, the Sherwood number (Sh) was measured under such conditions that the Reynolds (Re) and the Schmidt numbers (Sc) varied from 0.004 to 0.05 and from 1.8 × 10³ to 2.7 × 10³, respectively. We found that Sh is proportional to Re^α and Sc^β and that the correlation between these three nondimensional parameters is almost the same as those given by conventional literature equations. The values of α and β were close to those in the literature correlations, between 0.26 and 0.41 and between 0.31 and 0.36, respectively. The use of the Wilson–Geankoplis equation to estimate k_f values entails a relative error of ca. 15%. So, conventional literature correlations provide correct estimates of k_f in HPLC systems, even for particle sizes of the order of a micrometer.     

Model study on the pyridine-Dewar pyridine and some related photoisomerization reactions

The potential energy surfaces corresponding to the photochemical reactions of pyridine, phosphinine, and arsabenzene have been investigated by employing the CAS(6,6)/6-311G(d,p) and MP2-CAS-(6,6)/6-311++G(3df,3pd)//CAS(6,6)/6-311G(d,p) methods. The thermal (or dark) reactions of these reactant species have also been examined using the same level of theory. The mechanisms of drastic structural change in the excited- and ground-state reactions of pyridine, phosphinine, and arsabenzene and the differences between them are elucidated. The theoretical investigations suggest that conical intersections play a crucial role in their photoisomerization reactions. The results obtained allow a number of predictions to be made.     

Kinetic studies on the sulfate radical-initiated polymerization of vinyl acetate and 4-vinyl pyridine in the presence of silica nanoparticles

The photolysis of silica suspensions of pH approximately 8 containing peroxodisulfate ions leads to the generation of two "surface transients" with a distinct spectrum and reactivity. Time-resolved and continuous irradiation experiments of similar dispersions also containing variable concentrations of vinyl acetate (VA) or 4-vinyl pyridine (4-VP) allowed the evaluation of the contribution of silica/water interfacial reactions to the kinetics and structural pattern of polymers synthesized using sulfate radicals as initiators. The rate constants measured for the reactions of the surface transients with 4-VP are 1 order of magnitude higher than those of VA, despite the fact that both species show similar reactivity in homogeneous solution toward sulfate radicals. It is suggested that both the sorption capacity and the different specific interactions with the silica surface of 4-VP and VA contribute to the observed reaction rates. Micrometer-sized latex particles of 4-VP and VP showed higher stability and more homogeneous size distributions when obtained in the presence of silica nanoparticles. Under the experimental conditions required for obtaining polymer particles, both the contribution of the described interfacial reactions and the effect of silica adsorbed monomer on the initiation steps of the polymerization may be neglected. The importance of in situ adsorption of the oligomer/polymer chains to silica NP during the polymerization propagation steps in determining the particle morphology is discussed.     

Infrared study of chemisorption and reactivity of pyridine on haematite

Pyridine adsorption on α-Fe₂O₃ has been studied by IR spectroscopy. The splitting of the 8a band of chemisorbed pyridine at infrared beam temperature has been interpreted as due to the existence on the haematite surface of at least two types of Lewis acid sites, possibly tetrahedrically and octahedrically coordinated cations, with a medium electron acceptor strength.Chemisorbed pyridine undergoes chemical transformations under heating, producing at 150°C a species identified, from the comparison of its spectrum with that of bipyridyl chemisorbed on the same surface, as 2,2′-bipyridyl in cis form. The reaction is probably realized via radical-anion formation, so confirming the electron transfer ability of haematite surface.At 400°C both pyridine and bipyridyl transform into a new species, without the opening of pyridine rings.     

Molecular orbital study of hydrogen bonding and proton transfer in the system acetic acid - pyridine: isolated system and solvent effect

The intermolecular hydrogen bond and proton transfer of the system, acetic acid - pyridine was investigated by means of the semi-empirical PCILO (Perturbative Configuration Interaction using Localised Orbitals) method. A potential curve with a single minimum was found in the 1:1 complex of acetic acid - pyridine. The effect of specific solvation (within the so-called supermolecule approach) on the potential curves for proton transfer was studied in the systems, acetic acid - pyridine × nH₂0 (n=2,3). The PCILO calculations, in agreement with experiments, have shown that these systems also form simple hydrogen bonded complexes.     

超声波降解吡啶溶液

焦化厂的排污水中含有酚、氰、杂环化合物(吡啶、吲哚、喹啉等)等有害物质[1]。利用超声波的声空化作用降解有机污染物,是一种清洁、高效的新型处理方法[2]。本文研究了超声波降解吡啶模拟焦化废水。探讨了吡啶初始浓度、溶液pH、超声辐射时间及处理温度等对降解效果的影响及规律。1　实验部分1 1　实验仪器及试剂KQ 100型超声波发生器,昆山市超声波仪器厂;SG 600W型超声波清洗器,张家港超声仪器有限公司;PHS 3C型酸度计,萧山市凯利科学仪器有限公司;751G紫外/可见分光光度计,上海分析仪器厂;DDS 11A型电导率仪,上海雷磁新泾仪器…     

Kinetic and mechanistic study on the reaction of alkylcobaloximes with azoles

The kinetics of axial water substitution by azoles (pyrazole and 1,2,4-triazole) in three different cobaloximes, viz.trans-[Co(Hdmg)(2)(R)H(2)O] where Hdmg = dimethylglyoximate, R = PhCH(2), Et and CF(3)CH(2), were studied as a function of azole concentration, temperature and pressure in aqueous solution. The second order rate constants for the substitution of water in trans-[Co(Hdmg)(2)(R)H(2)O] for R = Et at pH 6.0, 25 degrees C and I= 0.1 M (NaClO(4)), were found to be 1309 and 1200 M(-1) s(-1) for pyrazole (Pz) and 1,2,4-triazole (Tz), respectively, and those obtained for R = PhCH(2) were found to be 755 and 691 M(-1) s(-1), respectively. The second order rate constants in the case of R = CF(3)CH(2) were found to be 0.358 and 0.348 M(-1) s(-1) for Pz and Tz, respectively. The relative order of reactivity for the different alkyls being Et > PhCH(2) > CF(3)CH(2). The activation parameters (DeltaH([not equal]), DeltaS([not equal]) and DeltaV([not equal])) obtained for these reactions were found to be in the range of 65-87 kJ mol(-1), 24-47 J mol(-1) K(-1) and 2.5-7.7 cm(3) mol(-1), respectively. These data suggest that an I(d) substitution mechanism operates where the azoles participate in the transition state.     

MNDO study on relative stabilities of monosubstituted pyridine tautomers

Relative stabilities of monosubstituted hydroxy-, mercapto- and aminopyridine tautomers have been calculated using the MNDO procedure with a full geometry optimization. In all cases considered the “lactim” tautomers proved to be more stable, in full qualitative agreement with the gas-phase experimental data.     

Kinetic regularities of catalytic ethylene polymerization on single- and multi-site cobalt and vanadium bis(imino)pyridine complexes

The number of active centers C _p in the homogeneous complexes LCoCl₂ and LVCl₃ (L = 2,6-(2,6-R₂C₆H₃N=CMe)₂C₅H₃N; R = Me, Et, ^t Bu) and the propagation rate constants k _p have been determined by the radioactive ¹⁴CO quenching of ethylene polymerization on these complexes in the presence of the methylaluminoxane (MAO) activator. For the systems studied, a significant portion of the initial complex (up to 70%) transforms into polymerization-active centers. The catalysts based on the cobalt complexes are single-site, and the constant k _p in these systems is independent of the volume of substituent R in the ligand, being (2.4?3.5) × 10³ L mol^?1 s^?1 at 35°C. The much larger molecular weight of the polymer formed on the complex with the tert-butyl substituent in the aryl rings of the ligand compared to the product formed on the complex with the methyl substituent is due to the substantial (～11-fold) decrease in the rate constant of chain transfer to the monomer. At the early stages of the reaction (before 5 min), the vanadium complexes contain active centers of one type only, for which k _p = 2.6 × 10³ L mol^?1 s^?1 at 35°C. An increase in the polymerization time to 20 min results in the appearance, in the vanadium systems, of new, substantially less reactive centers on which high-molecular-weight polyethylene forms. The number of active centers C _p in the 2,5-tBu₂LCoCl₂ and 2,6-Et₂LVCl₃ systems with the MAO activator increases as the polymerization temperature is raised from 25 to 60°C. The activation energies of the chain propagation reaction (E _p) have been calculated. The value of E _p for complex 2,5-tBu₂LCoCl₂ is 4.5 kcal/mol. It is assumed that the so-called “dormant” centers form in ethylene polymerization on the 2,6-Et₂LVCl₃ complex, and their proportion increases with a decrease in the polymerization temperature. Probably, the anomalously high value E _p = 14.2 kcal/mol for the vanadium system is explained by the formation of these “dormant” centers.     

A theoretical study of the electronic spectra of pyridine and phosphabenzene

The electronic excitation spectra of pyridine and phosphabenzene have been studied using theoretical methods. The electronic states are described by wave functions derived from second-order perturbation theory based on multiconfigurational reference functions. The study includes singlet and triplet valences excited states as well as a number of Rydberg states. For both molecules the transition energies to the two lowest * excited singlet states are known from experiment and reproduced with an accuracy of 0.15 eV or better, while then * transition energies are predicted with a somewhat uncertain error of about 0.2 eV. The calculations suggest the lowestn * transition detected experimentally in pyridine corresponds to an adiabatic transition. 43 electronic states have been determined in each of the molecules.     

Kinetic study of the pyrolysis of neoprene

Kinetics of neoprene thermal decomposition has been performed under dynamic conditions at different heating rates, between 5 and 80 °C/min in a TG apparatus. The same kinetic model has been applied simultaneously to runs performed at different heating rates and different atmospheres allowing a good correlation of the weight loss data. A mechanism based on three independent reactions has been used to model the thermal decomposition. The first reaction is of an order close to two, and the other two reactions are of order below one, similar to other plastic materials. Different alternatives for the mathematical treatment for fitting TG data were considered. The accuracy of the calculated kinetic parameters was studied by means of a sensibility analysis.     

Kinetic study of the formation of N-chloramines

We studied the kinetics of the chlorination of amines by sodium hypochlorite in strongly alkaline aqueous solution. A reaction mechanism compatible with experimental results is proposed and discussed. © 1995 John Wiley & Sons, Inc.     

FeOCl层状材料及其插层化合物:结构、性质与应用

氧基氯化铁(FeOCl)是一种典型的Fe基层状材料,于20世纪30年代被发现,并于20世纪70年代起作为一种优异的插层主体在超分子插层化学领域进行了大量的研究.FeOCl的层状结构赋予了其远比传统铁(氢)氧化物更加灵活的调变空间,自2013年第一次发现FeOCl具有优异的固体Fenton活性以来,围绕FeOCl及其插层...