Chlorination of substituted phenols with chloramine T. A kinetic study

Kinetics of chlorination of substituted phenols with a particular emphasis on p-nitrophenol (PNP) have been extensively studied using chloramine T (CAT). The effect of added mineral acids, neutral salts, and chloride have been investigated in detail. In aqueous acetic acid at high acidities the reactive phenols follow a zero-order process, while PNP or the disubstituted derivatives give a fractional-order dependence on substrate concentration. The concentration dependence of rate with respect to PNP, the chlorinating agent, and acid reveals the rate law 1/k_obs versus 1/[PNP] gave a straight line with a finite intercept. In aqueous dimethylformamide (DMF) and dimethylsulfoxide (DMSO) the reaction shows a second-order dependence on CAT and a first-order dependence on PNP in the case of DMF and a slight increment in order in DMSO. Addition of water increases the rate both in aqueous acetic acid and in dipolar aprotic solvents such as DMF and DMSO. The order of the reaction with respect to CAT is found to be dependent on pH as well as the reactivity of the phenols. In buffered acetic acid medium a second-order dependence on CAT was followed up to pH 7. The rate variations with temperature in the range of 30°¨Dot;50°C have been studied for all the substituted phenols, and the respective activation parameters have been calculated. The empirical rate law is accounted for by a mechanism involving species generated from CAT complexing PNP. Protonated CAT, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm Cl} $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Cl}\mathop {\rm O}\limits^{\rm + } {\rm AcH} $\end{document}, and dichloramine T (DCT) are considered important depending on reaction media. The effect of salts, pH, structural variations, and solvent dependence have been accounted for by the proposed mechanism. An attack by positive chlorine on oxygen of the phenol is the preferred mode of attack.     

Kinetic investigations on the reaction of pertechnetate with dimercaptosuccinic acid

The kinetics of the reaction of pertechnetate with racemic and mesodimercaptosuccinic acid in acidic solution have been studied. The reaction is first order in each reactant and is dependent on the acidity of the solution.

---

⁹⁹Tc- . . H_o .

     

A computational study of the heats of reaction of substituted monoethanolamine with CO2

Various amines have been considered as materials for chemical capture of CO(2) through liquid-phase reactions to form either carbamate or carbamic acid products. One of the main challenges in these CO(2)-amine reactions lies in tuning the heat of reaction to achieve the correct balance between the extent of reaction and the energy cost for regeneration. In this work, we use a computational approach to study the effect of substitution on the heats of reaction of monoethanolamine (MEA). We use ab initio methods at the MP2/aug-cc-pVDZ level, coupled with geometries generated from B3LYP/6-311++G(d,p) density functional theory along with the conductor-like polarizable continuum model to compute the heats of reaction. We consider two possible reaction products: carbamate, having a 2:1 amine:CO(2) reaction stoichiometry, and carbamic acid, having a 1:1 stoichiometry. We have considered CH(3), NH(2), OH, OCH(3), and F substitution groups at both the α- and β-carbon positions of MEA. We have experimentally measured heats of reaction for MEA and both α- and β-CH(3)-substituted MEA to test the predictions of our model. We find quantitative agreement between the predictions and experiments. We have also computed the relative basicities of the substituted amines and found that the heats of reaction for both carbamate and carbamic acid products are linearly correlated with the computed relative basicities. Weaker basicities result in less exothermic heats of reaction. Heats of reaction for carbamates are much more sensitive to changes in basicity than those for carbamic acids. This leads to a crossover in the heat of reaction so that carbamic acid formation becomes thermodynamically favored over carbamate formation for the weakest basicities. This provides a method for tuning the reaction stoichiometry from 2:1 to 1:1.     

A kinetic study of the reaction of O(3P) with toluene

The absolute rate constant of the reaction of O(³P) with toluene was measured by the microwave discharge-fast-flow method to obtain k_T = 10^{9.7–2.7/2.303RT} l./mole·sec at 100–375°C. This was in good agreement with the rate constant calculated from the combination of the relative rate constant obtained by Jones and Cvetanovic with the recently determined absolute rate constants of the reaction of O(³P) + olefins. The extrapolation of the above Arrhenius plot to 27°C was also in good agreement with the absolute value of k_T = 4.5 × 10⁷ l./mole·sec determined recently by Atkinson and Pitts at 27°C. The rate constant of the reaction of chlorobenzene with O(³P), obtained at 238°C as 10^8.3 l./mole·sec by a competitive method, was smaller than k_T by a factor of about two at the same temperature.     

A kinetic ESR study of the reaction of t-butylperoxy radicals with hexaphenylditin and hexaphenyldilead

Absolute rate constants for the reaction of t-butylperoxy radicals with hexaphenylditin and hexaphenyldilead have been found to fit the equations log (k_p/M⁻¹·s⁻¹) = (5.5±0.15) − (3800±150)/Θ and log (k_p/M⁻¹·s⁻¹) (9.5±0.3) − (6000±250)/Θ, where Θ = 2.303 RT cal mol⁻¹, respectively.     

A kinetic study of the decomposition of HNO3 and its reaction with NO

The rate of reaction between NO and HNO₃ and the rate of thermal decomposition of HNO₃ have been measured by FTIR spectroscopy. The measurements were made in a teflon lined batch reactor having a surface to volume ratio of 14 m^?1. During the experiments, with initial HNO₃ concentrations between 2 and 12 ppm and NO concentrations between 2 and 30 ppm, a reactant stoichiometry of unity and a first order NO and HNO₃ dependence were confirmed. The observed rate constant for the reaction at 22°C and atmospheric pressure was determined to 1.1 (±0.3) 10^?5 ppm^?1 min^?1. At atmospheric pressure, HNO₃ decomposes into NO₂ and other products with a first order HNO₃ dependence and with a rate constant of 2.0 (±0.2) 10^?3 min^?1. The apparent activation energy for the decomposition is 13 (±4) kJ mol^?1.     

A kinetic study for the reaction of aryloxytrimethylsilane with methanesulfinyl chloride giving aryl methanesulfinate

A nucleophilic attack of phenoxy-oxygen has been suggested as the mechanism of the reaction of aryloxytrimethylsilane with methanesulfinyl chloride.     

A kinetic study on the reaction of hydrogen with Mg2Ni

The kinetics of the reaction of hydrogen with Mg₂Ni has been investigated under hydrogen pressures from 3 up to 7 bar at various temperatures (548 ≤ T ≤ 593 K). Hydrogen absorption rates for the hydriding reaction show an inverse temperature dependence under our experimental conditions. The results are analyzed by considering the increase in temperature due to the heat of reaction in the course of hydrogen absorption. The rate-controlling step for hydriding reaction in the initial stage is the dissociative chemisorption on Ni involving heat transfer as “a rate-delaying step.” In later stages, hydrogen absorption rates decrease gradually with the effect of the particle size distribution and the diminution of the unreacted fraction. Other phenomena are also discussed, i.e., hydrogen absorption in α-solid solution region and an incubation period.     

A kinetic study of the reaction between formic acid and HoBr

The reaction between formic acid and HOBr in strongly acid aqueous media was studied by absorption spectrophotometry at 298 K. Bromine, the monitored species, displays a transient behavior, gradually rising up to a maximum and then decaying with first-order kinetics. Reaction rates, expressed as R = -dC_Br2/dt, depend on the concentrations of HCOOH (0.1–1.4M), HOBr (0.3–1.5 × 10^?3 M), and H⁺ (0.1–1.0M). The mechanism with k₁ =1.04 ± 0.20M^?1· s_?1, k₃ = 20.2M^?1, quantitatively accounts for all observations within experimental error.     

Oxidation of substituted phenethyl alcohols by sodium-N-chloro-p-toluene sulfonamide: A kinetic study

Summary The kinetics of the oxidation of sixp-substituted phenethyl alcohols (PEA, R=–H, –Cl, –Br, –CH₃, –OCH₃, and -NO₂) by sodium-N-chloro-p-toluene sulfonamide (chloramine-T,CAT) in the presence of HCl was studied at 35°C. The rate shows a first order dependence on [CAT]₀ and [H⁺]₀ and a fractional order in [PEA]₀ and [Cl^–]₀. Ionic strength variations, addition of reaction product toluene sulfonamide, and variation of the dielectric constant of the medium have no effect on the rate. The solvent isotope effect amounts to about 0.90. Proton inventory studies have been made in H₂O-D₂O mixtures. The rates correlate satisfactorily withHammett's relationship. The reaction constant was –3.3 for electron releasing substituents and –0.25 for electron withdrawing groups at 35°C. The activation parameters H ^#, S ^#, G ^#, and logA were derived. H ^# and S ^# are linearly related, and an isokinetic relationship is observed with =166.7K, indicating entropy as a controlling factor.

---

Die Oxidation substituierter Phenethylalkohole mit Natrium-N-chlor-p-toluolsulfonamid: Kinetische Untersuchungen

Zusammenfassung Die Kinetik der Oxidation von sechsp-substituierten Phenethylalkoholen (PEA), R=–H, –Cl, –Br, –OCH₃ und NO₂) mit Natrium-N-chlor-p-toluolsulfonamid (Chloramin-T,CAT) in Gegenwart von HCl bei 35°C wurde untersucht. Die Reaktionsgeschwindigkeit ist in bezug auf [CAT]₀ und [H⁺]₀ ester und hinsichtlich [PEA]₀ und [Cl]₀ gebrochener Ordnung. Variation der Ionenstärke, Zusatz von Reaktionsprodukt oder Toluolsulfonamid und Variation der Dielektrizitätskonstante des Mediums haben keinen Einfluß auf die Reaktionsgeschwindigkeit Der Lösungsmittel-Isotopeneffekt beläuft sich auf etwa 0.90. Die Protonenbilanz wurde in H₂O-D₂O Mischungen untersucht. Die Geschwindigkeiten korrelieren zufriedenstellend nach derHammettschen Beziehung. Die Reaktionskonstante wurde mit =–3.3 für elektronenabgebende und =–0.25 für elektronenanziehende Substituenten bei 35°C bestimmt. Die Aktivierungsparameter H ^#, G ^#, G ^# und logA wurden abgeleitet; H ^# und S ^# korrelieren linear, und eine isokinetische Beziehung mit =166.7K weist auf die Entropie als kontrollierenden Faktor hin.

     

F原子与i-C3H7I反应的动力学研究

本文利用交叉分子束技术和激光诱导萤光方法, 研究了F+i-C3H7I→IF+i-C3H7反应的动力学过程. 获得了产物IF相对初生振动分布和相对细致反应速率常数. 初生态布居接近于模型III下的统计理论斯待值, 这不仅表明反应经过长寿命“配合物", 而且也说明自由基i-C3H7的内态是激发的. 另外, 确定了反应的产物IF内部能量分配和总反应截面σ, σ=(3.6±0.5)×10^-^1^6cm^2.     

Relative-rate kinetic study of the reaction of bromine atom with neopentane

The rate coefficient ratio ofk ₁/k ₂=0.83±0.21 has been determined for the reactions Br+neo-C₅H₁₂ (1) and Br+C₂H₆ (2) by applying the relative-rate kinetic method atT=298 K.     

Direct kinetic study of the reaction of OH radicals with methyl-ethyl-ketone

The low-pressure discharge flow technique with resonance fluorescence monitoring of OH has been applied to study the kinetics of the overall reaction:

A kinetic study of the electron-transfer reaction of the phthalimide-N-oxyl radical (PINO) with ferrocenes

A kinetic study of the one-electron oxidation of a series of ferrocenes (FcX: X = H, CO2Et, CONH2, CH2CN, CH2OH, Et, and Me2) by PINO generated in CH3CN by reaction of N-hydroxyphthalimide (NHPI) with the cumyloxyl radical produced by 355 nm laser flash photolysis of dicumyl peroxide has been carried out. Ferrocenium cations were formed, and the reaction rate was determined by following the decay of PINO radical at 380 nm as a function of the FcX concentration. Rate constants were very sensitive to the oxidation potential of the substrates and exhibited a good fit with the Marcus equation, from which a lambda value of 38.3 kcal mol(-1) was calculated for the reorganization energy required in the PINO/ferrocenes electron-transfer process. Knowing the ferrocene/ferrocenium self-exchange reorganization energy it was possible to calculate a value of 49.1 kcal mol(-1) for the PINO/PINO- self-exchange reaction in CH3CN. Moreover, from the Marcus cross relation and the self-exchange rates of ferrocene and dimethylferrocene, the intrinsic reactivity of PINO in electron-transfer reactions has been calculated as 7.6 x 10(2) M(-1) s(-1). The implications of these values and the comparison with the electron-transfer self-exchange reorganization energies of peroxyl radicals are briefly discussed.     

A kinetic and product study of the Cl + HO2 reaction

Absolute rate data and product branching ratios for the reactions Cl + HO2 --> HCl + O2 (k1a) and Cl + HO2 --> OH + ClO (k1b) have been measured from 226 to 336 K at a total pressure of 1 Torr of helium using the discharge flow resonance fluorescence technique coupled with infrared diode laser spectroscopy. For kinetic measurements, pseudo-first-order conditions were used with both reagents in excess in separate experiments. HO2 was produced by two methods: through the termolecular reaction of H atoms with O2 and also by the reaction of F atoms with H2O2. Cl atoms were produced by a microwave discharge of Cl2 in He. HO2 radicals were converted to OH radicals prior to detection by resonance fluorescence at 308 nm. Cl atoms were detected directly at 138 nm also by resonance fluorescence. Measurement of the consumption of HO2 in excess Cl yielded k1a and measurement of the consumption of Cl in excess HO2 yielded the total rate coefficient, k1. Values of k1a and k1 derived from kinetic experiments expressed in Arrhenius form are (1.6 +/- 0.2) x 10(-11) exp[(249 +/- 34)/T] and (2.8 +/- 0.1) x 10(-11) exp[(123 +/- 15)/T] cm3 molecule(-1) s(-1), respectively. As the expression for k1 is only weakly temperature dependent, we report a temperature-independent value of k1 = (4.5 +/- 0.4) x 10(-11) cm3 molecule(-1) s(-1). Additionally, an Arrhenius expression for k1b can also be derived: k1b = (7.7 +/- 0.8) x 10(-11) exp[-(708 +/- 29)/T] cm3 molecule(-1) s(-1). These expressions for k1a and k1b are valid for 226 K < or = T < or = 336 and 256 K < or = T < or = 296 K, respectively. The cited errors are at the level of a single standard deviation. For the product measurements, an excess of Cl was added to known concentrations of HO2 and the reaction was allowed to reach completion. HCl product concentrations were determined by IR absorption yielding the ratio k1a/k1 over the temperature range 236 K < or = T < or = 296 K. OH product concentrations were determined by resonance fluorescence giving rise to the ratio k1b/k1 over the temperature range 226 K < or = T < or = 336 K. Both of these ratios were subsequently converted to absolute numbers. Values of k1a and k1b from the product experiments expressed in Arrhenius form are (1.5 +/- 0.1) x 10(-11) exp[(222 +/- 17)/T] and (10.6 +/- 1.5) x 10(-11) exp[-(733 +/- 41)/T] cm3 molecule(-1) s(-1), respectively. These expressions for k1a and k1b are valid for 256 K < or = T < or = 296 and 226 K < or = T < or = 336 K, respectively. A combination of the kinetic and product data results in the following Arrhenius expressions for k1a and k1b of (1.4 +/- 0.3) x 10(-11) exp[(269 +/- 58)/T] and (12.7 +/- 4.1) x 10(-11) exp[-(801 +/- 94)/T] cm3 molecule(-1) s(-1), respectively. Numerical simulations were used to check for interferences from secondary chemistry in both the kinetic and product experiments and also to quantify the losses incurred during the conversion process HO2 --> OH for detection purposes.     

In situ electrogeneration of o-benzoquinone and high yield reaction with benzenethiols in a microflow system

We have successfully demonstrated that a microflow reactor is extremely useful in controlling reactions involving an unstable o-benzoquinone. The key features of the method are an effective o-benzoquinone generation and its rapid use for the following reaction without decomposition in a microflow system.     

A kinetic and product study of the gas-phase reaction of ozone with vinylcyclohexane and methylene cyclohexane

The gas-phase reaction of ozone with vinylcyclohexane and methylene cyclohexane has been investigated at ambient T and p=1 atm of air in the presence of sufficient cyclo-hexane or 2-propanol added to scavenge OH. The reaction rate constants, in units of 10⁻¹⁸ cm³ molecule⁻¹ s⁻¹, are 7.52±0.97 for vinylcyclohexane (T=292±2 K) and 10.6±1.9 for methylene cyclohexane (T=293±2 K). Carbonyl reaction products were cyclohexyl meth-anal (0.62±0.03) and formaldehyde (0.47±0.04) from vinylcyclohexane and cyclohexanone (0.55±0.10) and formaldehyde (0.60±0.05) from methylene cyclohexane, where the yields given in parentheses are expressed as carbonyl formed, ppb/reacted ozone, ppb. The sum of the yields of the primary carbonyls is close to the value of 1.0 that is consistent with the simple mechanisms: O₃+cyclo(C₆H₁₁)−CH(DOUBLEBOND)CH₂→α(HCHO+cyclo(C₆H₁₁)CHOO)+(1−α)(HCHOO+cyclo(C₆H₁₁)CHO) for vinylcyclohexane and O₃+(CH₂)₅C(DOUBLEBOND)CH₂→α(HCHO +(CH₂)₅COO)+(1−α)(HCHOO+(CH₂)₅C(DOUBLEBOND)O) for methylene cyclohexane. The coefficients α are 0.43±0.10 for vinylcyclohexane and 0.52±0.05 for methylene cyclohexane, i.e., (formaldehyde+the substituted biradical) and (HCHOO+cyclohexyl methanal or cyclo-hexanone) are formed in ca. equal yields. Reaction rate constants, carbonyl yields, and reaction mechanisms are compared to those for alkene structural homologues. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 855–860, 1997     

A substituent effects study reveals the kinetic pathway for an interfacial reaction

This paper describes the use of a substituent effects study to understand the mechanistic basis for an interfacial Diels-Alder reaction that does not proceed with standard second-order kinetics. Cyclopentadiene (Cp) undergoes a Diels-Alder reaction with a chemisorbed mercaptobenzoquinone to yield an immobilized Diels-Alder adduct. The pseudo-first-order rate constants are not linearly related to the concentration of diene, but they reach a limiting value with increasing concentrations of diene. The results of a substituent effects study support a mechanism wherein the electrochemical oxidation of hydroquinone produces two states of quinone. The first form, Q*, either reacts with Cp or isomerizes to Q, a form that is significantly less reactive with the diene. The interfacial reaction reaches a maximum rate when the concentration of diene is sufficiently high so that Q* undergoes complete Diels-Alder reaction and does not isomerize to Q. This work provides an example of the use of physical organic chemistry to understand an interfacial reaction.