Kinetics and mechanism of oxidation of chromium(III)-tetraoxalylurea complex by periodate

A novel chromium(III) complex of tetraoxalylurea was prepared. In aqueous solutions, [Cr^III(H₂L)(H₂O)]⁺ (H₂L = diprotonated tetraoxalylurea) is oxidized by IO ₄ ^– according to the rate law

Reactions of alkoxy and hydroxy radicals generated photochemically from hydroperoxide molecules

In the present work as well as HRO^. radicals were generated in the photochemical interaction of 1,2-benzanthracene with -ethyl phenyl hydroperoxide /HROOH/ in C₆H₆ and CCl₄ at 304 K. radicals were trapped by C₆H₆. The main reaction of HRO^. radicals is hydrogen abstraction from the hydroperoxide group of HROOH. Although OH radicals are less selective, the hydrogen abstraction is the main process during their interaction with aromatics in contrast to reactions in aqueous solutions, where addition to the benzene ring is the rate-determining process in CCl₄:

Osmium(VIII) oxidation of arsenic(III) in aqueous sulphuric acid

The oxidation of As^III by Os^VIII or Os^VI in aqueous H₂SO₄ follows the rate law:

Dissociation Constants of Protonated Cysteine Species in NaCl Media

The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [ CH(CH₂SH)COOH; H₃B⁺]. The values of dissociated constants, p , for protonated cysteine species (H₃B⁺ H⁺ + H₂B, K ₁; H₂B H⁺ + HB^–,K ₂; HB^– H⁺ + B^2–,K ₃) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5–6.0 mol-(kgH₂O)^–1 and between 5, and 45°C. The equations

Nonisothermal membrane phenomena across perfluorosulfonic acid-type membranes,Flemion S: Part II. Thermal membrane potential and transported entropy of ions

Thermal membrane potentials across the perfluorosulfonic acid-type membrane, Flemion S, were measured for HCl, alkali metal chlorides, and ammonium and methyl ammonium chlorides. The difference between the mean molar transported entropy of the counterions in the membrane and the partial molar entropy of the counterions in the external solution was determined from the experimental data on thermal membrane potential, thermoosmosis and electroosmosis. The sign of the thermal membrane potential in HCl solution varies from positive to negative with the concentration. In HCl and alkali metal chloride solutions, the order of their thermal membrane potentials (–/T) is H⁺>Li⁺=Na⁺>K⁺ which is roughly the inverse of that of the crystallographic radii of the ions. However, the order of their entropy differences is H⁺>Na⁺>K⁺>Li⁺ which is just the inverse of that of their thermoosmotic coefficients (D) or the entropy difference of water in thermoosmosis. For the ammonium and methyl ammonium ion forms, the orders of both –/T and increase with an increasing number of methyl groups: (CH₃)₄N⁺>(CH₃)₃NH⁺>(CH₃)₂NH ₂ ⁺ > CH₃NH ₃ ⁺ >NH ₄ ⁺ , which is also the inverse of that ofD or .     

Catalytic Mechanism of the “Noncatalytic” Autooxidation of Sulfite

Iron ions are shown to play a special role among transition metal ions in the oxidation of sulfite by oxygen. The thermodynamically favorable formation of chain carriers S : FeOH²⁺+ HSO₃ ^– Fe²⁺+ H₂O + , H _{r 298} ⁰ –250 kJ/mol accompanied by the regeneration of the active Fe(III) form in the reactions of Fe(II) with and HSO₅ ^–provides the efficient catalytic mechanism for sulfite consumption even at [Fe]₀ 10^–8mol/l. Any aqueous solution contains iron ions in this amounts. Thus, the noncatalytic oxidation of sulfite is in fact the catalytic reaction involving unavoidable microadmixtures of iron ions. Other transition metal ions (Mn²⁺, Co²⁺, etc.) can only enhance the catalytic effect of iron admixture.     

Integral heats of solution and enthalpies of ionization of 100% nitric acid at 298 K 3. Aqueous solutions of sulfuric acid containing 70–90% H2SO4 and ionization of HNO3 as a base

The integral heats of solution of 100% HNO₃ at =0.1mole/liter in aqueous solutions of H₂SO₄ of <90% by wt. were measured. A scheme was proposed and proved for ionization of HNO₃ as a base in 82–90% aqueous solutions of H₂SO₄, according to which un-ionized HNO₃ exists in the form of an aqueous solvate H₂O-HNO₃ and the ionized form as the ion pair NO₂ ⁺·HSO₄ ^–. The value of the enthalpy of ionization of nitric acid H(NO₂ ⁺ HSO₄ ^–)=H(NO₂ ⁺·HSO₄ ^–) drops from 2.05 at 89.99% H₂SO₄ to 0.18 kcal/mole in 84.07% H₂SO₄.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 306–310, February, 1990.     

Solubility of Siderite (FeCO3) in NaCl Solutions

The solubility of siderite (FeCO₃) at 25°C under constant CO₂ partial pressure [p(CO₂)] was determined in NaCl solutions as a function of ionic strength. The dissolution of FeCO₃(s) for the reaction

Interaction of singlet oxygen with α-and β-naphthols

The oxidation of - and -naphthol/PhOH/ sensitized by protoporphirin has been studied in benzene and Ccl₄ at 25 °C by a laser flash photolysis apparatus with a time resolution of 10 ns. Kinetics of the¹O₂ decay in the presence and in the absence of PhOH was followed spectrophotometrically by using 1,3-diphenylizobenzofurane /DPBF/ as an acceptor for¹O₂. The effective rate coefficients/k_eff/of the consumption of DPBF were measured as a function of the concentration of PhOH. In CCl₄ the value of k_eff remained practically unchanged after the addition of PhOH at a concentration of 10^–5–10^–4M, at the same time short-lived intermediates were formed which absorb at 400 nm in such solutions. In benzene at [PhOH]<4×10^–2M 5×10⁵M^–1s^–1 and 1×10⁵M^–1s^–1, as it has been calculated. Long-lived intermediates have not been observed in C₆H₆.     

Kinetics and mechanism of the oxidation of hydrogen peroxide by the octacyanotungstate(V) ion in alkaline aqueous media

Summary The oxidation of H₂O₂ by [W(CN)₈]^3– has been studied in aqueous media between pH 7.87 and 12.10 using both conventional and stopped-flow spectrophotometry. The reaction proceeds without generation of free radicals. The experimental overall rate law, , strongly suggests two types of mechanisms. The first pathway, characterized by the pH-dependent rate constant k _s, given by , involves the formation of [W(CN)₈· H₂O₂]^3–, [W(CN)₈· H₂O₂·W(CN)₈]^6– and [W(CN)₈· HO]^3– intermediates in rapid pre-equilibria steps, and is followed by a one-electron transfer step involving [W(CN)₈·HO]^3– (k _a) and its conjugate base [W(CN)₈·O]^4– (k _b). At 25 °C, I = 0.20 m (NaCl), the rate constant with H _a =40±6kJmol^–1 and S _a =–151±22JK^–1mol^–1; the rate constant with H _b =36±1kJmol^–1 and S _b =–136±2JK^–1mol^–1 at 25 °C, I = 0.20 m (NaCl); the acid dissociation constant of [W(CN)₈·HO]^3–, K ₅ =(5.9±1.7)×10^–10 m, with and is the first acid dissociation constant of H₂O₂. The second pathway, with rate constant, k _f, involves the formation of [W(CN)₈· HO₂]^4– and is followed by a formal two-electron redox process with [W(CN)₈]^3–. The pH-dependent rate constant, k _f, is given by . The rate constant k ₇ =23±6m ^–1 s ^–1 with and at 25°C, I = 0.20 m (NaCl).     

Kinetics of the manganese(III)-oxalate reaction in acidic sulphate media

The kinetics of the reaction of manganese(III) with oxalic acid (OA) has been studied in H₂SO₄ solutions. Under the experimental conditions of 6 × 10^–3 <>₀ < 0.4=" mol=">^–3 and [H₂SO₄]₀ 0.2 mol dm^–3 the observed pseudo-first order rate constant k _obs follows the expression

Ion-molecular interactions in the HCl—isopropanol system

Multiple Attenuated Total Reflectance (MATR) IR spectra of solutions of HCl in isopropanol, containing 0 to 43 mol. % HCl, were studied in the 900–4000 cm^–1 range. The addition of HCl to PrⁱOH yields proton disolvates with strong symmetrical H-bonds. At high concentrations of HCl (C _HCl ⁰ > 5.7 mol L^–1, /C⁰ _HCl < 2), when the number of alcohol molecules is not enough to form disolvates with all of the protons present in the solution, (Cl...H...Cl)^– ions are formed, in addition to (C₃H₇OH)₂H⁺. The spectra of these ions have been assigned.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1753–1756, September, 1995.This work was carried out with financial support of the Russian Foundation for Basic Research (Project No. 93-03-18356).     

Studies on mixed ligand complexes of cobalt(II), nickel(II), copper(II) and zinc(II) involving 8-hydroxyquinoline-5-sulphonic acid as a primary ligand and substituted catechols as secondary ligands

Summary Stability constants (K _MAL ^MA ) and other thermodynamic parameters of the MAL complexes (charges omitted) [M=Co^II, Ni^II, Cu^II or Zn^II; AH₂=8-hydroxyquinoline-5-sulphonic acid; LH₂=catechol (L¹H₂), 1,2-dihydroxybenzene-sulphonate (L²H₂), 1,2-dihydroxybenzene-3, 5-disulphonate (L³H₂), 4-nitro-1,2-dihydroxybenzene (L⁴H₂)] have been determined at 25°C and at an 0.1 M KNO₃ ionic strength by the extended Irying-Rossotti technique. The stability constants lie in the sequences: K_{MAL}^{MA} ?K_{ML_2 }^{ML} ; K_{MAL}^{MA_1 } > K_{MAL}^{MA_2 } > K_{MAL}^{MA_3 } \gg K_{MAL}^{MA_4 } $$ " align="middle" border="0"> and all follow the Irving-Williams stability order. These observations can be explained in terms of electrostatic interaction, change of electrophilicity of the bound metal and -acidic character of the primary ligand.     

Excess partial molar volumes and thermal expansivities in the water-rich region of aqueous 2-butanone

Excess partial molar volumes of 2-butanone V _m ^E (B) and thermal expansivities _p were measured in the water-rich region of aqueous 2-butanone. The composition derivatives of both quantities showed anomalies at about X _B =0.033 (x _B is the mole fraction of B). showed a step anomaly, while exhibited a peak anomaly. The compositions at which these anomalies occurred match those of the step anomalies observed earlier in and in aqueous 2-butanone. These results are discussed in comparison with those obtained previously for aqueous 2-butoxyethanol.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

α-Ketothioketene dimers

Conclusions When,-dichlorovinyl ketones are reacted with Na₂S, NaSC(S)N(C₂H₅)₂, KSC(S)OC₂H₅, and NaSCOCH₃, two types of sulfur-containing heterocyclic compounds are formed: 1,3-dithietanes and 1,3-dithiols , at which time the ratio of the products depends on the nature of the sulfur-containing nucleophilic reagent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2940–2048, September, 1976.     

Influence of solvents on the parameters of the NMR spectra of Vinca alkaloids. V

Summary On the basis of the results of a study of the influence of various solvents on the parameters of the NMR spectra of some hydroxyindole alkaloids, the following characteristic values of for the protons have been found:a) for C₁₉-CH₃ in the allo bases is +0.18 ppm; b) in the epiallo bases it is +0.36 ppm; c) for CO₂CH₃ in the allo bases is +0.30 to +0.37 ppm; d) in the epiallo bases it is +0.19 ppm; and e) for the 11-OCH₃ group in the hydroxyindoles is +0.44 to +0.52 ppm.It has been established that in the epiallo bases benzene causes a diamagnetic shift, and in the allo bases a paramagnetic shift, of the H₁₉ signal. It is possible to perform a stereochemical identification of the hydroxyindole alkaloids on the basis of the value of for C₁₉-CH₃, CO₂CH₃, and H₁₉ protons.Analysis of the signals of the aromatic protons of vineridine in C₆D₆ solution and in a number of other solvents has permitted their assignments to be refined and a long-range (allyl) coupling of the H₁₇ and H₁₅ protons with an SSCC of 2.0 Hz that is characteristic of the epiallo alkaloids to be found. It has been shown that the change in the CSs of the protons of rings D and E of the hydroxyindole alkaloids and the indole alkaloid reserpinine as a result of the influence of various solvents mainly has a symbatic nature. The invariability of the SSCCs of the protons in the solvents investigated with the exception of solutions in TFA, shows that the conformations of rings C, D, and E in them do not change. The changes in the CSs and SSCCs of the protons in the alkaloids investigated in TFA are an indication of the isomerization of these compounds in the acid.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 360–368, May–June, 1977.     

Effect of the concentration of polybasic aminoanilides and aminobenzimidazoles on the acidity functionH 0 of aqueous solutions of HCl

The effect of the concentrations of the reactants and reaction products on the protonating ability of aqueous HCl is investigated in the example of the cyclization of polybasic aminoanilides to aminobenzimidazoles at 25°C and 50°C. It is established that the acidity functionH ₀ ^s of HCl solutions in organic-aqueous solvents of constant composition is equal toH ₀, the acidity function for an aqueous solution with the same concentration of HCl on the mole-ratio scale. This can be utilized for the quantitative prediction ofH ₀ ^s. The decrease in the basicity of indicators in mixed solvents is a consequence of the decrease in the activity coefficient of the unionized form of the base standardized to water _B. It is observed that not onlyH ₀ ^s but also the basicity constant of the reactant may vary during the reaction. The latter depends on the concentration of the reactant, as well as on the effect of the product concentration on the value of _B for the reactant.Deceased April 8, 1991.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 488–491, March, 1993.     

An <Emphasis Type="Italic">ab initio </Emphasis> Quantum-Chemical Study of C<Subscript>6</Subscript>H<Subscript>5</Subscript>S(O)CH<Subscript>3</Subscript> and C<Subscript>6</Subscript>H<Subscript>5</Subscript>S(O)CF<Subscript>3</Subscript>

The potential functions of internal rotation around the C -S bond in the C₆H₅S(O)CH₃ and C₆H₅S(O)CF₃ molecules were obtained by ab initio MP2(full)/6-31+G* calculations. The stationary points were identified by solving the vibrational problems. The structures in which the plane of the C -S-C bonds is approximately perpendicular to the benzene ring plane correspond to the energy minimum. The barriers to rotation around the C -S bond, corrected for the zero-point vibration energy, are 21.29 [C₆H₅S(O)CH₃] and 28.98 [C₆H₅S(O)CF₃] kJ mol⁻¹. The bond angles (deg) are as follows: 95.7 (CSC), 107.1 (C SO), 106.3 (C SO) in C₆H₅S(O)CH₃; 93.5 (CSC), 108.2 (C SO), 105.2 (C SO) in C₆H₅S(O)CF₃. The bond lengths are as follows (Å): 1.520 (S=O), 1.804 (C -S), 1.810 (C -S) in C₆H₅S(O)CH₃; 1.507 (S=O), 1.799 (C -S), 1.870 (C -S) in C₆H₅S(O)CF₃. According to the results of NBO calculations, the formally double S=O bond consists of a strongly polarized covalent σ bond (S→O) and an almost ionic bond. An increase in the S=O bond multiplicity relative to a single bond is mainly due to hyperconjugation by the mechanism n(O)→σ*(C -S) and n(O)→σ*(C -S) and, to a lesser extent, by interaction of the oxygen lone electron pairs with the Rydberg orbitals of the S atoms, characterized by a large contribution of the d component.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 1, 2005, pp. 96–104.Original Russian Text Copyright © 2005 by Bzhezovskii, Il’chenko, Chura, Gorb, Yagupol’skii.     

Kinetic studies of the oxidation ofN-(2-hydroxycyclohexyl)-ethylenediaminetriacetatochromate(III) by periodate

The kinetics of the oxidation of [Cr^III(H₂O)(XOH)], (XOH=N-(2-hydroxycyclohexyl)ethylenediaminetriacetate) to Cr^VI by periodate have been investigated in aqueous solution at various pH values (6.00–7.20) and temperatures (15.0–35.0°C). The reaction follows the rate law: