Kinetic study of the bromine-catalyzed alcoholysis of butoxytriethylsilane: n-Butoxy group–s-butoxy group exchange reaction

In order to compare the catalytic activity of bromine with those of iodine and iodine monohalides, kinetic studies on the reaction, Et₃SiOBuⁿ + Bu^sOH ? Et₃SiOBu^s + BuⁿOH, were undertaken. Pseudo first-order rate constants were determined at 0°, 10°, 15°, 20°, and 30°C by means of gas chromatography on the reaction mixtures containing both butanols in excess. From the observed rate constants, the catalytic coefficients of bromine were evaluated as follows: The enthalpies and entropies of activation were estimated to be (42.0 – 42.2) kJ/mol, ?(103 – 104) J/K (forward reaction), and (40.4 ? 40.7) kJ/mol, ? (101 ? 102) J/K (reverse reactions). These data suggest that bromine is much more active than iodine and iodine monohalides, and its high activity was interpreted on the basis of the structure of the reaction intermediate.     

Synthesis of statistical glycidyl methacrylate‐n‐vinyl pyrrolidone copolymers and their reaction with naproxen

Free‐radical copolymerization of glycidyl methacrylate (GMA) with N‐vinylpyrrolidone (VPD) was carried out at 50 °C using 3.0 mol · L^?1 of N,N′‐dimethylformamide solution and 9.0 · 10^?3 mol · L^?1 of 2,2′‐azobisisobutyronitrile as an initiator. The modification reaction of GMA‐VPD copolymers with a model bioactive carboxylic acid, 6‐methoxy‐α‐methyl‐2‐naphthaleneacetic acid (naproxen), was studied in the homogeneous phase using basic catalysts. The influence of the type of catalyst and the GMA content was evaluated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1192–1199, 2002     

Kinetics of reaction between acetic acid and Ag2+ in nitric acid medium

The reaction kinetics between acetic acid and Ag²⁺ in nitric acid medium is studied by spectrophotometry. The effects of concentrations of acetic acid (HAc), H⁺, NO^?₃, and temperature on the reaction are investigated. The rate equation has been determined to be –dc(Ag²⁺)/dt = kc(Ag²⁺)c(HAc)c^?1(H⁺), where k = (610 ± 15) (mol/L)^?1 min^?1 with an activation energy of about (48. 8 ± 3.5) kJ mol^?1 when the reaction temperature is 25°C and the ionic strength is 4.0 mol L^?1. The reduction rate of Ag²⁺ increases with the increase in HAc concentration and/or temperature and the decrease in HNO₃ concentration. However, the effect of NO^?₃ concentrations within 0.5–2.5 mol L^?1 on the reaction rate is negligible. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 47–51, 2013     

Study on mechanism for oxidation of <Emphasis Type="Italic">N,N</Emphasis>-dimethylhydroxylamine by nitrous acid

The oxidation of N,N-dimethylhydroxylamine (DMHAN) by nitrous acid is investigated in perchloric acid and nitric acid medium, respectively. The effects of H⁺, DMHAN, ionic strength and temperature on the reaction are studied. The rate equation in perchloric acid medium has been determined to be −d[HNO₂]/dt = k[DMHAN][HNO₂], where k = 12.8 ± 1.0 (mol/L)⁻¹ min⁻¹ when the temperature is 18.5 °C and the ionic strength is 0.73 mol/L with an activation energy about 41.5 kJ mol⁻¹. The reaction becomes complicated when it is performed in nitric acid medium. When the molarity of HNO₃ is higher than 1.0 mol/L, nitrous acid will be produced via the reaction between nitric acid and DMHAN. The reaction products are analyzed and the reaction mechanism is discussed in this paper.     

Investigation of the structure and energy of β-diketonates. XIV. Composition of overheated vapors and the molecular structure of monomeric yttrium tris-hexafluoroacetylacetonate Y(C5O2HF6)3

Simultaneous electron diffraction and mass spectrometry along with a quantum chemical (DFT/B3LYP) calculation are applied to study the molecular structure of yttrium tris-hexafluoroacetylacetonate Y(hfa)₃. The superheating of the vapor in a double two-temperature effusion cell shows that up to a temperature of ∼200°C ions containing from one to three metal atoms are formed, and the most intensive ion has the stoichiometry of (Y₂L₅)⁺ at a temperature below ∼120°C. The monomer starts to noticeably decompose at temperatures above 330°C.The electron diffraction patterns of monomers are obtained at T _exp = 208(5)°C. According to the results of theoretical and experimental investigations, Y(hfa)₃ molecule has D ₃-symmetry. The rotation angle of triangular O-O-O faces with respect to their position in the regular prism is equal to 14.4(1)°C. The values of internuclear distances and valence angles (r _h1-geometry) are: r(Y-O) = 2.259(6) Å, r(C-O) = 1.263(6) Å, r(C-C_r) = 1.413(4) Å, r(C-C_F) = 1.531(4) Å, r(C-F) = 1.344(3) Å, O-Y-O = 75.2(2)°, O-C-C_F = 113.8(2)°, C-C_F-F = 112.4(2)°. The results of quantum chemical calculations are well consistent with the experimental data. Original Russian Text Copyright ? 2007 by G. V. Girichev, V. V. Rybkin, N. V. Tverdova, S. A. Shlykov, N. P. Kuz’mina, and I. G. Zaitseva __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 5, pp. 871–879, September–October, 2007.     

Li,K‖Cl,MoO4 ternary mutual system

Phase equilibria in the Li,K‖Cl,MoO₄ ternary mutual system were studied by differential thermal analysis (DTA). The characteristics of the following three ternary eutectics were determined: E ₁: 348°C, 41 mol % KCl, 7.75 mol % Li₂MoO₄, and 51.25 mol % LiCl; E ₂: 475°C, 44 mol % KCl, 17.25 mol % Li₂MoO₄, and 38.75 mol % LiCl; and E ₂: 477°C, 35 mol % KCl, 47 mol % Li₂MoO₄, and 18 mol % LiCl.     

A study of the thermal cure of a phenylethynyl-terminated imide model compound and a phenylethynyl-terminated imide oligomer (PETI-5)

The kinetic mechanism of the thermal cure of a phenylethynyl-terminated imide model compound, 3,4′-bis[(4-phenylethynyl)phthalimido]diphenyl ether (PEPA-3,4′-ODA) and a phenylethynyl-terminated imide oligomer PETI-5 (MW 5000 g/mol) was studied. FTIR was used to follow the cure of the model compound, while thermal analyses (DSC) was used to follow the cure of the PETI-5 oligomer. The changes in IR absorbance of phenylethynyl triple bonds at 2214 cm⁻¹ of PEPA-3,4′-ODA as a function of cure time were detected at 318, 336, 355, and 373°C, respectively. The changes in the glass transition temperature, T_g, of PETI-5 as a function of time were measured at 350, 360, 370, 380, and 390°C, respectively. The DiBenedetto equation was applied to define the relative extent of cure, x, of the PETI-5 oligomer by T_g. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 40.7 kcal/mol as determined by infrared spectroscopy. For PETI-5, the reaction followed 1.5th order, yielding an activation energy of 33.8 kcal/mol for the whole cure reaction, as determined by T_g using the DiBenedetto method. However, the cure process of PETI-5 just below 90% by this method followed first-order kinetics yielding an activation energy of 37.2 kcal/mol. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 461–470, 1998     

A study on the kinetics of condensation reaction of cardanol and formaldehyde,part I

Novolac resins having cardanol‐to‐formaldehyde mole ratios of 1:0.4, 1:0.5, and 1:0.6 were prepared by using aromatic sulphonic acid as the catalyst at four different temperatures ranging between 90°C and 120°C, with an interval of 10°C. Free formaldehyde and free phenol contents were determined at regular time intervals to check the completion of the reaction. The synthesized novolacs were characterized by Fourier‐transform infrared spectroscopic analysis, nuclear magnetic resonance, and gel permeation chromatography. The reaction between cardanol and formaldehyde was found to follow second‐order kinetics. The overall rate constant (k) increased with the increase of temperature. On the basis of the value of k, various other activation parameters such as activation energy (E_a), change in enthalpy (ΔH), entropy (ΔS), and free energy (ΔG) of the reaction were also evaluated. It was found that the condensation reaction of cardanol and formaldehyde with aromatic sulphonic acid was nonspontaneous and irreversible. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 559–572, 2009     

Formation constants and coordination thermodynamics for binary complexes of Cu(II) and some α-amino acids in aqueous solution

In this study, the formation constants of 1?:?1 binary complexes of Cu(II) with L-glutamic acid, L-aspartic acid, glycine, L-alanine, L-valine, and L-leucine and 1?:?2 binary complexes of L-glutamic acid, glycine and the protonation macro- and microconstants of all these amino acids were determined potentiometrically in aqueous solutions at 5.0, 20.0, and 35.0°C at a constant ionic strength of I?=?0.10?mol?L^?1 (NaClO₄). The thermodynamic parameters ΔG _f°, ΔH _f°, and ΔS _f° were determined for the protonation of all amino acids used in this study and for the complex formation reactions of them with Cu(II). The results were analysed by means of Principle of hard and soft [Lewis] acids and bases. Additionally, in order to confirm the complex formation and determine the stability constants of complexes, UV-Vis spectroscopic studies were carried out. The stability constants obtained by spectrophotometrically are confirmed by those determined potentiometrically.     

Determination of propagation‐rate constant of vinylidene chloride by emulsion polymerization

The propagation‐rate constant of vinylidene chloride (VDC) was determined at 40 and 50 °C, respectively, by applying the so‐called Ugelstad plot to the polymerization‐rate data of the seeded and unseeded emulsion polymerizations of VDC. The values of the propagation‐rate constant k_p thus determined are k_p = 64 dm³/mol · s at 50 °C and k_p = 52 dm³/mol · s at 40 °C, respectively. From these k_p values, the activation energy for propagation reaction was determined to be E_p = 4.2 kcal/mol, which is close to that of vinyl chloride (3.7 kcal/mol). © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1005–1015, 2001