Kinetics and mechanism of oxidation of copper(I) ions with thiuram disulfide

The kinetics of the oxidation of copper(I) perchlorate with thiuram disulfide (tds) in acetonitrile and its mixtures with benzene or ethyl bromide have been investigated. It has been shown that the rate of the reaction is limited by the inner-sphere transfer of an electron from the copper(I) ion to tds in a complex of the type [Cu^I(tds)]⁺. The subsequent dissociation of the anionradical tds —proceeds rapidly and leads to the formation of copper(II) dithiocarbamate which is recorded in the absorption spectra and by EPR. The rate constant of electron transfer has been determined (3·10^–4sec^–1) and it was found that it is practically independent of the polarity of the medium. The absence of such a correlation is attributed to the negligible energies of reorganization of the solvent in the inner-sphere electron transfer.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 450–455, July–August, 1988.     

Reactivity of carbocations from 1,2-dihydroquinolines in binary mixtures of methanol with pentane and acetonitrile

The rate constants and activation parameters of the reactions of the carbocation resulting from 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline photolysis with methanol (k ₁) and the methoxide ion (k ₂) have been measured by flash photolysis in binary mixtures of methanol with inert solvents (nonpolar pentane and polar acetonitrile) in wide composition ranges. The changes in the activation parameters for k ₁ at different solvent compositions show that the increase in the rate constant in the pentane mixtures is mainly deter-mined by the increase in the preexponential factor. The decrease in k ₁ in the acetonitrile mixtures is deter-mined by the decrease in the methanol concentration and by the increase in the activation energy. The different roles of the methoxide ion in the reaction are demonstrated. They depend on the nature of the inert solvent in the mixture. The results of this study are considered in terms of methanol clustering in pentane and acetonitrile, the different solubilities of 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline in the components of the binary mixtures, and the difference in distribution and solvation between the carbocation and the methoxide ion in the mixtures.     

Determination of the Absolute Rate Constants of Reactions between Diphenyl Carbonyl Oxide and Alcohols by Flash Photolysis

The rate constants of the reactions of diphenyl carbonyl oxide Ph₂COO with a number of alcohols and water in acetonitrile, benzene, andn-decane solutions (295 K) were measured by flash photolysis. The rate constants vary over a range from 400 (triphenylmethanol in a MeCN solution) to 2.5 × 10⁵ l mol^–1 s^–1 (adamantanol in a benzene solution). -Methoxydiphenylmethyl hydroperoxide is the reaction product of Ph₂COO and MeOH. The absence of a kinetic isotope effect and the dependence of the logarithms of the rate constants on the first ionization potentials of alcohols are indicative of the formation of a C–O bond at the rate-limiting step of the reaction.     

The Solvent Effect on the Rate of Reaction between Propanethiol and Chlorine Dioxide

The products and kinetics of the liquid-phase oxidation of propanethiol by chlorine dioxide in organic media (n-heptane, 1,4-dioxane, carbon tetrachloride, benzene, diethyl ether, ethyl acetate, acetone, and acetonitrile) at temperatures from –10 to 70°C were examined. The reaction rate constants and activation parameters were measured in the above solvents. A strong solvent effect on the reaction kinetics was found (k= 1.67 × 10^–3or 52.7 l mol^–1s^–1(25°C) in heptane or acetonitrile, respectively). The data were analyzed in terms of the Leydler–Eyring and Koppel–Palm equations. The formation of high-polarity intermediates in the test reaction was suggested.     

Initial state and transition state solvation effects in the cobaltitungstate oxidation of iodide in binary aqueous solvent mixtures

Summary Rate constants are reported for 12-tungstocobaltate(III) [CoW₁₂O₄₀]^5– oxidation of iodide in water and in binary aqueous solvent mixtures containing up to 40% methanol, 40% acetonitrile, or 60% dimethyl sulphoxide. From these kinetic results, solubility measurements on potassium 12-tungstocobaltate(III), and published data on Gibbs free energies of transfer of appropriate ions, it has been deduced that the dominant factor in determining the marked decrease in rate observed on going from water into the binary aqueous solvent mixtures is destabilisation of the transition state for the electron-transfer reaction.     

Effect of the nature of inert solvent on the decay kinetics of the carbocation generated in the photolysis of 1,2-dihydroquinolines in methanol

The dependence of the quantum yield and the decay rate constant for the carbocation generated in the photolysis of 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline (6-EtO-DHQ) in methanol on the solvent composition was studied in the mixtures of methanol with isopropanol, acetonitrile, and pentane by pulse photolysis. The addition of these solvents decreases the yield of the carbocation and differently affects the kinetic parameters of its decay. The carbocation decay in the mixtures MeOH-i-PrOH and MeOH-C₅H₁₂ is described by the pseudo-first order equation (k ₁), with the dependence of k ₁ having a maximum at 50 vol % of MeOH in the MeOH-i-PrOH mixtures, and k ₁ increasing with a decrease in the MeOH concentration in the MeOH-C₅H₁₂ mixtures. In the MeOH-MeCN mixtures, the value of k ₁ decreases with a decrease in the MeOH concentration, and, at the concentration of MeOH lower than 50 vol %, the contribution of the second-order reaction (k ₂) is observed. The activation energies and preexponential factors were determined in the MeOH-C₅H₁₂ mixtures of different compositions, and it was shown that E _act practically did not depend on the solvent composition and were close to E _act for other carbocations obtained in MeOH. The increase in k ₁ with a decrease in the MeOH concentration is caused by an increase in the preexponential factor. The results were discussed on the basis of the reaction mechanism involving the competing reactions of the carbocation combination with two nucleophilic particles, the MeOH molecule and the MeO⁻ anion. The composition of the mixture and the nature of the inert solvent affect strongly the course of these reactions. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 411–416. The article was translated by the authors.     

Rate and Equilibrium of Acetyl Group Exchange between Pyridines and Pyridine N-Oxides

22 Acetyl group exchange reactions between N-acetoxypyridinium salts and 4-dimethylaminopyridine, 4-morpholinopyridine, and N-methylimidazole in acetonitrile at 298 K have been studied. The rate constants varied from 10⁵ to 10^–4 L/mol·s, and the equilibrium constants ranged from 10⁹ to 10^–9. The rates and equilibrium constants of these reactions did not comply with the Brönsted equation. The kinetics of the acetyl exchange reactions are well described by a correlation equation containing squared terms.     

Estimation of electron transfer rate constants by static (optical and electrochemical) measurements

A kinetic study of the reduction of Co(NH₃)₅(DMSO)³⁺ (DMSO=dimethylsulfoxide) by Fe(CN)₆⁴⁻ has been carried out in several water–cosolvent mixtures at 298.2 K. The cosolvents used were ethylene glycol, acetonitrile, methanol and glucose. The free energies of activation for this thermal electron-transfer reaction have been calculated from a combination of spectroscopic and electrochemical data and compared with those obtained from the kinetic study. Quantitative agreement is found between both series of data. This shows the possibility of estimating activation free energies for electron transfer reactions from these (static) measurements.     

Complex Formation of Crown Ethers with Cations in Water–Organic Solvent Mixtures. III. Thermodynamics of Interaction Between Na+ Ion with 15-Crown-5 Ether in Water–Acetonitrile Mixtures at 25°C

Enthalpies of solution of 15-crown-5 ether in the acetonitrile–water–sodium iodide system have been measured at 25°C. The equilibrium constants of complex formation of 15C5 with sodium iodide have been determined by molar conductance at various mole ratios 15C5 to sodium iodide in mixtures of water with acetonitrile at 25°C. The thermodynamic functions for complexation of the crown ether with Na⁺ were calculated. From the result, the standard Gibbs energies of complex formation as a function of the normalized Lewis acidity parameters E ^N _T and enthalpy of solvation of 15C5 in the mixtures of water with acetonitrile have been analyzed. The enthalpies of transfer of the 15C5 complex with sodium iodide from pure acetonitrile to the mixtures studied were calculated and discussed.     

On the role of solvent in complexation equilibiria. II. The acid-base chemistry of some sulfhydryl and ammonium-containing amino acids in water—acetonitrile mixed solvents

The macroscopic and microscopic acid-base chemistry of a series of sulfhydryl and ammonium-containing amino acids HS–R–NH₃ [R=–CH₂CH(COOH)–, cysteine (CYS); R=–C(CH₃)₂CH(COOH)–, penicillamine (PEN); R=–CH(COOH)CH₂CH₂CONHCH(–CH₂)CONHCH₂COOH, glutathione (GSH)] was characterized in water and its binary mixtures with acetonitrile (16.3, 34.2, and 53.9 mass % acetonitrile). Macroscopic acid dissociation constants were obtained by potentiometric titration using the glass-calomel electrode pair. Microscopic acid dissociation constants were calculated from ultraviolet absorption measurements at ca. 232 nm where the deprotonated sulfhydryl group absorbs. The macroscopic constants decrease uniformly as the solvent becomes enriched in acetonitrile. The microscopic constants, which characterize the relative concentrations of the two monoprotonated tautomers of the molecules (I and II) reveal that as the solvent becomes enriched in acetonitrile, the fraction of molecules existing as highly charged tautomer I decreases for CYS (0.68–0.40), PEN (0.85–0.34), and GSH (0.61–0.30). These results are related to the decreasing concentration of water as the solvent becomes enriched in acetonitrile.     

Flash Photolysis of Diphenyldiazomethane in the Presence of Organic Sulfides

The flash photolysis of diphenyldiazomethane in acetonitrile, benzene, and n-decane solutions saturated with air resulted in the formation of diphenyl carbonyl oxide Ph₂COO which decayed in combination reactions. In the presence of organic sulfides, the transfer of the terminal oxygen atom of Ph₂COO to the sulfur atom was observed. The kinetics of this reaction was studied. The absolute rate constants (k ₆, dm³ mol^–1 s^–1) of the reactions of Ph₂COO with sulfides at 295 K (acetonitrile as a solvent) varied from 4.1 × 10² (Me₂S) to 8.1 × 10⁴ (Ph₂S). The solvent effect on the reaction kinetics and product composition was studied. The mechanism of the process was discussed.     

Solvent effect on the kinetics of oxidation of [Co(en)2amS]2+ by IO4−

The dependence of the rate constants for the oxidation of [Co(en)2amS]2+ (amS=–SCH2CH2NH2 2– by IO4– on solvent composition has been established for aqueous mixtures of MeOH, i-PrOH, t-BuOH, urea (U), ethylene carbonate (EC), acetonitrile (AN), dimethyl formamide (DMF) and acetone (Me2CO). Addition of aprotic cosolvents leads to marked decrease in the reaction rate in comparison to monohydroxylic alcohols. Alcohols inhibit the reaction rate in order MeOH < i-PrOH < t-BuOH. The change in solvation on going from the initial to the transition state are discussed in terms of the Gibbs transfer function, Gt0.     

Effect of the nature of the solvent on the enthalpy characteristics of solvation of conformationally flexible 1,7-diaza-18-crown-6 molecules

Enthalpy changes during dissolution of 1,7-diaza-18-crown-6 (L) in benzene, MeCN, DMSO, methanol, and water have been determined calorimetrically. Standard enthalpies of solution at infinite dilution were calculated and used for analysis of enthalpies of solvation of L in solvents of different natures. The effect of self-association of the solvent, polarization of its molecules, and specific solvation on the concentration dependence of the enthalpies of solution are discussed. Specific interaction of L with methanol and water molecules through H-bonds is established. The concentration dependence of the enthalpies of solution in benzene and acetonitrile are sensitive to conformational equilibria over the range 0–5.10^–4 mole/kg.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2262–2264, October, 1991.     

Kinetics,mechanism, and products of the reaction of diphenylcarbonyl oxide with carboxylic acids

The kinetics of the reactions of acetic, benzoic, formic, oxalic, malic, tartaric, trifluoroacetic, and hydrochloric acids with diphenylcarbonyl oxide Ph₂COO was studied. The carbonyl oxide Ph₂COO was generated by flash photolysis of diphenyldiazomethane Ph₂CN₂ in solutions of acetonitrile and benzene at 295 K. The apparent rate constants of the reaction range from 4.6·10⁸ for (COOH)₂ in MeCN to 7.5·10⁹ L mol^–1 s^–1 for acetic acid in a benzene solution. The reaction mechanism was proposed, according to which at the first stage the carbonyl oxide is reversibly solvated by the solvent. Then the solvated carbonyl oxide reacts with the acid molecule by the mechanism of insertion at the O—H bond.     

Conductance and Thermodynamic Study of Thallium and Silver Ion Complexes with Crown Ethers in Different Binary Acetonitrile–Water Solvent Mixtures

The complexation reactions between Ag⁺ andTl⁺ ions with 15-crown-5 (15C5) and phenyl-aza-15-crown-5(PhA15C5) have been studied conductometrically in 90%acetonitrile-water and 50% acetonitrile - water mixed solvents attemperatures of 293, 298, 303 and 308 K. The stability constants of theresulting 1 : 1 complexes were determined, indicating that theTl⁺ complexes are more stable than the Ag⁺complexes. The enthalpy and entropy of crown complexation reactions were determined from the temperature dependence of the complexation constants.The enthalpy and entropy changes depend on solvent composition and the T S⁰ _o–H⁰ plotshows a good linear correlation, indicating the existence of entropy –enthalpy compensation in the crown complexation reactions.     

Kinetic characteristics of initiated oxidation of limonene

The kinetics of oxygen absorption .n the process of limonen (4-isopropenyl- l-methulcyclohex-1-ene) oxidation was studied in chlorobenzene solution at 40–80 °C. The values of the kinetic parameters of oxidation and the activation energy (38.1 kJ mol^–1) have been determined. The nonlinear dependence of the rate of the oxidation of limonene on its concentration has been established, The rate constants of the chain termination reactions were estimated by chemiluminescence techniques.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1676–1681, July, 1996.     

Conductance Study of Complexation of Lead Ions by Several 18-Membered Crown Ethers in Acetonitrile-Dimethyl Sulfoxide Mixtures Between 25 and 55°C

A conductance study of the interaction between Pb²⁺ ion and 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexyl-18-crown-6 (DC18C6), aza-18-crown-6 (A18C6), diaza-18-crown-6 (DAI8C6), dibenzopyridino-18-crown-6 (DBPy18C6), and dibenzyldiaza-18-crown-6 (DBzDA18C6) in acetonitrile–dimethyl sulfoxide mixtures was carried out at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance–mole ratio data and found to vary in the order DA18C6 > A18C6 > DBzDA18C6 > DC18C6 > 18C6 > B18C6 > DBPy18C6. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the resulting complexes are enthalpy stabilized, but entropy destabilized. A linear relationship is observed between log K _f of different complexes and mole fraction of acetonitrile in the solvent mixtures. The TS ⁰ vs. H ⁰ plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of an enthalpy–entropy compensation in the complexation reactions.     

Nonlinear fluorescence quenching of newly synthesized coumarin derivative by aniline in binary mixtures

The fluorescence quenching of newly synthesized coumarin (chromen-2-one) derivative, 4-(5-methyl-3-phenyl-benzofuran-2-yl)-6-chloro-chromen-2-one (MPBClC) by aniline in different binary solvent mixtures of benzene and acetonitrile have been reported by steady state fluorescence measurements. All the measurements were carried out at room temperature (296 K). A positive curvature from linearity was observed in the Stern–Volmer (S–V) plot in all the solvent mixtures. Various rate parameters for the fluorescence quenching have been determined by sphere of action static quenching model and finite sink approximation model. The results show that the positive curvature in the S–V plot is due to both static and dynamic quenching processes. Further, with the use of finite sink approximation model, it is concluded that these bimolecular reactions are diffusion-limited.     

Kinetics of the Dissolution of Silver in Thiocarbamide Solutions

The dependence of the rate of solution of silver on the pH of the solution, the ratio of the iron(III) and thiocarbamide concentrations, and the temperature has been determined. The rate constants for the solution of silver (k _i = 2.3·10^–4 to 9.6·10^–4s^–1) at temperatures from 283-298 K have been calculated and from the temperature dependence of the rate constant the activation energies have been calculated: 68.84 kJ/mol for kinetic control of the rate of solution and 26.06 kJ/mol in the adsorption inhibition region.     

FORMATION AND DISSOCIATION KINETICS OF THE STRONTIUM(II) COMPLEX OF CRYPT AND C222 IN BINARY DIMETHYLSULFOXIDE-ACETONITRILE MIXTURES

Abstract

The dissociation and the formation rates of the Sr ²⁺ - C222 cryptate in different dimethylsulf-oxide-acetonitrile mixtures have been studied spectrophotometrically using murexide as a metallochromic indicator. In all solvent mixtures used, the ratio of the rate constants for dissociation and formation of the cryptate was found to be in agreement with the formation constants obtained by an independent equilibrium spectrophotometric technique. The activation parameters E _a, δH ^? and δS ^? for the formation and dissociation of the cryptate were determined from the temperature dependence of the corresponding rate constants, and found to be strongly solvent dependent. There is a linear relationship between the logarithm of the formation constant as well as the activation parameters and the mol fraction of acetonitrile in the mixed solvent.