Kinetic study of the iodine-catalyzed alcoholysis of Butoxytriethylsilane: n-butoxy group—s-butoxy group exchange reaction

In order to appreciate the excellent catalytic effect of iodine on the alcoholyses of alkoxysilanes more precisely, the rates of the reaction, Et₃SiOBuⁿ + Bu^sOH ? Et₃SiOBu^s + BuⁿOH, were determined at various iodine concentrations. Both forward and reverse reactions are first order with respect to butoxysilane and to butanol, and pseudo first-order rate constants were measured at 40°, 30°, and 20°C on reaction mixtures containing both butanols in excess by means of gas-liquid chromatography. The observed rate constants as a function of iodine concentration gave linear relationships, and from these data the catalytic coefficients of iodine were evaluated: The enthalpies and the entropies of activation were estimated to be 53.2 kJ mol^?1, ?103 J K^?1 mol^?1 (forward, 30°C) and 51.8 kJ mol^?1, minus;100 J K^?1 mol^?1 (reverse, 30°C).     

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.     

Kinetic study of the electrophilic reaction of trialkyltin chlorides and iodine monochloride

The kinetics of the electrophilic substitution of several trialkyltin chlorides by iodine monochloride are presented. Rate constants have been determined at four different temperatures and the activation parameters A, E_a, and ΔS°⁼ are calculated. A mechanism is proposed involving charge-transfer as the driving force for the substitution. © 1993 John Wiley & Sons, Inc.     

Kinetic study of hydroxylamine-bromate ion reaction in acid sulfate solution—a competitive consecutive reaction

A kinetic study of oxidation of hydroxylamine by bromate ion in acid sulfate solution using spectrophotometric and potentiometric methods is reported. Oxidation of hydroxylamine to nitrate is quantitative and followed competitive, consecutive, and auto catalytics steps characterized by induction periods. In the slow rate limiting step, hydroxylamine on reaction with HOBr (k) forms an intermediate I, which further reacts fast with second molecule of HOBr (k) giving nitrite. Nitrite reacts with HOBr (k) yielding the final product nitrate. Nitric acts as an autocatalyst also and its initial addition decreased the induction periods. In excess of hydrogen ion concentration all the reaction steps follow second-order kinetics. All the second-order rate constants are reported and the reaction mechanism is proposed.     

Theoretical study on the reaction mechanism of the alcoholysis of isocyanates

In this paper, the reactions of HNCO or CH₃NCO with methanol have been studied using the ab initio MO method. The geometries of the reactants and products have been optimized by the energy gradient method. The calculated results are in accordance with experiment. Using Powell's method, by the minimization of the Euclidean norm σ of the gradient, the structures of the transition state (TS ) for the two reactions were obtained. The structures have been further confirmed as TS by finding that there is one and only one negative eigenvalue for their force constant matrix. The imaginary vibration mode corresponding to the TS was also discussed. The calculated activation barriers of these two reactions are 96.02 and 95.13 kJ/mol, respectively. It can be concluded that the alcoholysis reaction of isocyanate is a nucleophilic addition reaction with methanol as an electronic donor and isocyanate as an acceptor and that the hydroxyl hydrogen of CH₃OH plays an important role in the reaction.     

Kinetic study of the reaction of OH with HCl from 240–1055 K

Absolute rate coefficients for the reaction of OH with HCl (k₁) have been measured as a function of temperature over the range 240–1055 K. OH was produced by flash photolysis of H₂O at λ > 165 nm, 266 nm laser photolysis of O₃/H₂O mixtures, or 266 nm laser photolysis of H₂O₂. OH was monitored by time-resolved resonance fluorescenceor pulsed laser–induced fluorescence. In many experiments the HCl concentration was measured in situ in the slow flow reactor by UV photometry. Over the temperature range 240–363 K the following Arrhenius expression is an adequate representation of the data: k₁ = (2.4 ± 0.2) × 10^?12 exp[?(327 ± 28)/T]cm³ molecule^?1 s^?1. Over the wider temperature range 240–1055 K, the temperature dependence of k₁ deviates from the Arrhenius form, but is adequately described by the expression k₁ = 4.5 × 10^?17 T^1.65 exp(112/T) cm³ molecule^?1 s^?1. The error in a calculated rate coefficient at any temperature is 20%.     

Reactivity of di‐iodine toward thiol: Desulfuration reaction of 5‐nitro‐2‐mercapto‐benzimidazole upon reaction with di‐iodine

The reaction of 2‐mercapto‐benzoic acid (H₂MBA), 2‐mercato‐nicotinic acid (H₂MNA), and 2‐mercapto‐pyrimidine (PMTH) with a twofold molar amount of di‐iodine (I₂) results in the isolation of crystals of the neutral disulfides of formulae: {(HMBA)₂·1/2(CH₃CN)} ( 1 ), {(HMNA)₂·(H₂O)} ( 2 ), and (PMT)₂ ( 3 ), respectively, when dichloromethane/acetonitrile/methanol ( 1 ) or dichloromethane ( 2,3 ) were used as solvents. The reaction of di‐iodine with thethiol PMTH and 2‐mercapto‐benzothiazole (MBZTH) yields the disulfide (PMT)₂ ( 3 ), and the di‐iodine adduct of formula {[MBZTH‐I₂]·[MBZTH]₂} ( 4 ), respectively. The reaction of di‐iodine with 5‐nitro‐2‐mercapto‐benzimidazole (O₂N‐MBZIMH) ( 5 ) in the presence of ferric trichloride hydrate (FeCl₃·6H₂O), in a 6:3:1 (I₂:thiol:FeCl₃·6H₂O) molar ratio, results in cocrystal ( 6 ), which contain the desulfurated hydroxyl derivative O₂N‐BZIMOH ( 6a ) and unreacted O₂N‐MBZIMH ( 6b ) in a 3:1 molar ratio. The compounds were characterized by elemental analysis, FT‐IR, and ¹H NMR spectroscopy. The crystal structures of compounds 1 – 6 were also determined by X‐ray crystallography. Cyclic voltammetry measurements showed that thiols with low oxidation potentials (< 1.0 V) mainly form disulfides upon a reaction with di‐iodine, whereas those with higher oxidation potential form charge transfer (CT), resulting in desulfurated products, MBZIMH. However, in the case of O₂N‐MBZIMH a desulfurated species was isolated. The formation of the final product also requires the presence of FeCl₃. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:498–511, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21042     

Kinetic study of ion exchange reaction between lysozyme and carboxymethyl Sephadex C-25

The ion-exchange reaction of lysozyme with carboxymethyl Sephadex C-25 was followed by conductivity change as a function of time just after the rapid mixing of the protein solution with the Sephadex suspension. A single relaxation process was observed; the conductivity increased exponentially with time in the 100 s scale. In this process, protons were released from the Sephadex C-25 in the same time scale. The relaxation process slowed down with an increase in the lysozyme concentration, but it quickened upon the addition of HCl. On the other hand, the potential on the Sephadex C-25 surface changed from a negative value to a positive one with an increase in the amount of lysozyme adsorbed on the surface. On the basis of these data, the relaxation process was attributed to the ion-exchange reaction of lysozyme with several protons of carboxymethyl groups of the Sephadex.     

Gas‐phase pyrolytic reaction of 3‐phenoxy and 3‐phenylsulfanyl‐1‐propanol derivatives: Kinetic and mechanistic study

3‐Phenoxy‐1‐propanols 1a–c and 3‐phenylsulfanyl‐1‐propanols 2a–c containing primary, secondary, and tertiary alcohols were prepared and subjected to gas‐phase pyrolysis in a static reaction system. Pyrolysis of 4‐phenyl‐1‐butanol 3 , 2‐methyl‐3‐phenyl‐1‐propanol 4 , and 2‐methyl‐3‐phenylpropanoic acid 5 was also studied, and results were compared with those obtained for compounds 1–3 . The pyrolytic reactions were homogeneous and followed a first‐order rate equation. Analysis of the pyrolysate showed the products to be phenol (from 1a to 1c ), thiophenol (from 2a to 2c ), and toluene (from 3 to 5 ) and carbonyl compounds. The kinetic results and product analysis of each of the nine investigated compounds are rationalized in terms of a plausible transition state for the elimination pathway. © 2007 Wiley Periodicals, Inc. 40: 51–58, 2008     

Kinetic study of the hydroxyl radical-propene reaction

Absolute rate coefficients for the reactions of OH with C₃H₆ and C₃D₆ were measured at temperatures from 293 to 896 K and at pressures from 25 to 600 Torr helium. Mechanistic information of importance to atmospheric and combustion modeling was obtained.     

Kinetic studies in mass spectrometry—IV. The [M — Cl] reaction in substituted chlorobenzenes and the question of molecular ion isomerization.

The [M]⁺˙ → [M ? Cl]⁺ reaction in a series of m- and p-X substituted chlorobenzenes has been studied, utilizing a simple kinetic approach, comparison of metastable ion relative abundances, and by measurement of ionization and appearance potentials. All evidence obtained is consistent with rearrangement prior to cleavage in the molecular ions, in which substituent position becomes effectively randomized. These findings are related to known hydrogen randomization reactions occurring in either the molecular ion or [M ? Cl] ion of chlorobenzenes. Mechanisms involving carbon scrambling via such species as ionized benzvalenes or prismanes, or ring-opening to isomeric acyclic molecular ions in which hydrogen randomization might occur can be entertained, but mechanisms involving simple hydrogen shifts in the intact benzene ring appear less likely.     

Kinetic study of the recombination reaction OD + NO2 + M → DNO3 + M

Rate constants for the recombination reaction OD + NO₂ + M → DNO₃ + M have been determined in the falloff region (5–500 torr) and at 297 ± 2 K, in the presence of He, N₂, and SF₆ as third bodies, by using a pulsed laser photolysis-resonance absorption technique. Values of k₀, k_x and the falloff parameter F_c have been estimated. Our rate constants were, within the experimental uncertainty, the same as those reported for the reaction of OH radicals with NO₂.     

Furan ring opening — isocoumarine ring closure: A recyclization reaction of 2‐carboxyaryldifurylmethanes

A general method for the synthesis of isocoumarine derivatives has been developed. Bis(5‐R‐2‐furyl)methylbenzoic acids (R = methyl, ethyl) underwent recyclization and subsequent cyclization into tetracyclic isochromene‐1‐one derivatives under treatment with hydrogen chloride in methanol. It has been shown that intermediate 4‐(5‐R‐furan‐2‐yl)‐3‐(3‐oxo‐3‐R‐propyl)‐isochromene‐1‐ones can be obtained selectively by varying a concentration of the hydrogen chloride and reaction times. In the case of R = tert‐butyl only corresponding 4‐[5‐(tert‐butyl)‐2‐furyl]‐3‐(4,4‐dimethyl‐3‐oxopentyl)‐1‐isochromenones were isolated regardless of the reaction conditions.     

Rearrangement reaction of the hydroxyl group of ω-hydroxy-alkyltriphenyl phosphonium bromides

No molecular ion peak from the Electron Impact lonization of eight co-hydroxyalkyltriphenyl phosphonium bromides(Ph3P (CH2)nOHBr-,n=2-6,8-10)can be found,except a part of some relative powerful fragment ions can be observed only.Each compound forms a very characteristic ion(O=PPbj-1) at m/z 277 through hydroxyl rearrangement reaction.The intensity of this ion is closely related with the size of the carbon chain of hydroxyalkyl and with temperature of ion source and temperature of sample probe.The above rearrangement reaction and the reaction to form ion at m/z 262 take place simultaneously,thus leading to strong competition.At n=2,ion at m/z 277 is the most powerful and becomes continuously the base peak.At n=3 and n=4,the intensity of ion at m/z 262 reaches the maximum,and is always the base peak,and the relative abundance of m/z 277 is only around 2%.At n=5,6,8,9,10,m/z 277 becomes base peak when the temperature of probe is below 300℃.But,when the temperature increases from 300℃to 350℃,m/z 262 sud     

Kinetic analysis of a slow electron transfer coupled with a father—son reaction

The electrode reaction mechanism involving interaction of the products of a slow, rate-determining electron transfer with the parent molecule (father—son reaction) has been examined theoretically under the conditions of cyclic voltammetry. The kinetic analysis indicates how to determine the correct values of the kinetic parameters for both the heterogeneous charge transfer and the homogeneous chemical step. The irreversible cathodic reaction of diphenylmethylphenylsulphide in anhydrous DMF provides a good example of this mechanism, since the diphenylmethyl carbanion resulting from the irreversible two-electron reduction undergoes proton transfer from the parent molecule (self-protonation mechanism).     

Kinetic study of the γ radiolysis of polyethylene

A kinetic study was made of the formation of hydrogen and trans-vinylene unsaturation in the radiolysis of polyethylene induced by γ rays with a dose rate of 6.35 × 10⁵ rad/hr at 30–100°C in vacuo. The rates of the formation of hydrogen and trans-vinylene unsaturation were described by the zero-order formation kinetics with respect to each concentration combined with the first-order disappearance. The apparent rate constant for the formation of hydrogen increased gradually with rising irradiation temperature to give the activation energy of 0.6 kcal/mole. On the other hand, those for the disappearance of hydrogen and the formation and disappearance of trans-vinylene unsaturation were almost independent of temperature. The G values for crosslinking and main-chain scission were obtained from the gel data by using the Charlesby-Pinner equation, and the activation energy of 1.5 kcal/mole was given for both of them. On the basis of these results the reactions induced by γ rays in solid polyethylene were discussed.     

多孔物质气固反应动力学研究

利用自主研制的微型流化床反应分析仪（MFBRA）在等温条件下测试了高比表面活性炭氧化反应,并根据基于固体转化的热分析动力学方法及考虑气体在微孔内扩散与反应的应用化工动力学方法求算了动力学参数．在内外扩散抑制最小化的实验条件下,粒径小于5μm的活性炭在700-1000℃的燃烧反应动力学研究表明,根据微型流化床中实验数据,采用等温热分析动力学方法求算得内扩散控制区活化能约为95kJ／mol;弓l入化工动力学方法中的随机孔模型对低温区等温燃烧数据拟合,可得孔结构参数在0．17m^-3左右,反应活化能为178kJ／mol,约为内扩散反应活化能的两倍,最为接近本征的碳燃烧反应活化能．