Studies on intermolecular interactions of metal chelate complexes. Part X. Interactions of metal chelates with ozone

Summary The interactions of more than forty metal chelate complexes, dithiocarbamates, dithiophosphates and acetylacetonates, with ozone are studied in homogeneous phase and the stoichiometry and the rate constants of the reactions estimated. Most powerful ozone deactivators are nickel(II) and copper(II) dithiocarbamate and dithiophosphate complexes interacting with 6.5 moles ozone per mole of the ligand with rate constant >0⁶m · I^–1 · s^–1. The remote ligand substituents do not influence the reaction parameters. Other sulphur-containing complexes of iron(III), cobalt(II), cobalt(III), zinc(II), manganese(III), bismuth(III), antimony(III), arsenic(III), cadmium(II), platinum(II), palladium(II) and chromium(III) deactivate 3–4 moles ozone per mole ligand with rate constants of 10²–10⁴ m · I^–1 · s^–1. Acetylacetonate complexes of copper(II), nickel(II), cobalt(III), iron(III), chromium (III), and oxovanadium(II) deactivate 1–3 moles ozone per mole ligand with a rate constant of 10–10⁴ m · I^–1 · s^–1. Using e.p.r. and electronic spectra, some intermediate products are detected and the mechanism of the reaction is discussed. The reported data are compared with other widely used antiozonants and the metal chelates are shown to have several advantages.     

Kinetics and stoichiometry of the reaction between ozone and C70 fullerene in CCl4

The kinetics and stoichiometry of the reaction between C₇₀ fullerene and ozone have been studied. The reaction obeys a bimolecular rate law. The stoichiometric coefficients of the reaction are 1: 12 to 1: 22, depending on reaction conditions. The rate constant at 22°C is 5 × 10⁴ l mol^?1 s^?1 for the first stage of fullerene conversion and (0.8–0.6) × 10⁴ l mol^?1 s^?1 for the subsequent stages. Since the stages differ in terms of reaction rate, the original C₇₀ molecules are first involved in the reaction, whereas, at the subsequent stages, all molecules are involved with equal probabilities, irrespective of the number of preceding reaction events in which they have participated.     

Oxidative cleavage of α, β-unsaturated compounds by pentachlorohydroxoplatinate(IV) in alkaline medium

The kinetics of oxidation of α,β-unsaturated compounds by platinum(IV) in the presence of alkali {[OH⁻]= (1–9) × 10⁻³ mol dm⁻³} have been investigated over the 303–318 K temperature range . The rate of the reaction is dependent on the first power of the concentrations of substrates, oxidant, and alkali. The rate constant increases with an increase in ionic strength and also with increasing dielectric constant of the medium. The oxidation rates follow the order: –CN > –CONH₂ > –COO⁻. The values of the third order rate constant (k₃) for the oxidation of acrylonitrile, acrylamide and acrylate are 1.24, 0.826 and 0.628 mol⁻² dm⁶ s⁻¹ respectively, at 303 K. The oxidations of the substrates by PtCl₅(OH)²⁻ take place by an inner-sphere mechanism. Platinum(IV) is reduced to platinum(II) by the substrates in a one-step two-electron transfer process to give reaction products. The major reaction product, HCHO, is identified from the reaction mixture using i.r. spectrometry, n.m.r. and C, H, N analysis. A tentative reaction mechanism, leading to the formation of products, has been suggested. The activation parameters of the reaction have been evaluated.     

Retro-Bingel reaction in the electrochemical reduction of bis(dialkoxyphosphoryl)methanofullerenes

Four steps of reduction were detected for bis(diethoxyphosphoryl)- and bis(diisopropoxyphosphoryl)methano[60]fullerenes (1, 2) and bis(diethoxyphosphoryl)methano[70]fullerene (3) by cyclic voltammetry in the o-dichlorobenzene—DMF (3 : 1, v/v)/Bu₄NBF₄ (0.1 mol L^–1) system on a glass-carbon electrode. At the first step the reversible transfer of one electron affords stable radical anions 1 and 2 (g = 1.9999, H = 1.9 G). When two electrons per molecule are transferred, the methano fragment is rapidly eliminated (retro-Bingel reaction). This process involves the step-by-step cleavage of two C—C bonds of exo-carbon with the fullerene shell in combination with the stepwise transfer of other two electrons and a proton to form finally the carbanion of the methano fragment and fullerene dianion. For all studied compounds, the elimination rate is much higher than that for bis(alkoxycarbonyl)- and dialkoxyphosphoryl(alkoxycarbonyl)methano[60]fullerenes, which makes it possible to propose bisphosphorylmethane groups as protective in synthesis of new fullerene derivatives.     

Quenching excited triplet C60 fullerene by tetracyanoethylene in benzonitrile

Quenching excited triplet³C₆₀ fullerene by tetracyanoethylene (TCNE) in a benzonitrile solution proceeds with a rate constant equal to (4.2±0.3) · 10¹⁸ (M · s)^–1. The formation of a radical ion pair [C₆₀ ⁺ · · · TCNE^–] was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1228–1230, July, 1993.     

Flash photolysis of chloride complexes of Cu(II) in organic solvents

By means of flash photolysis and low-temperature spectrophotometry, the formation of a complex between a Cu(I) ion and a peroxy radical of the solvent has been detected in ethanol, isopropanol, and dimethylformamide. The peroxy radical is generated in a reaction of a solvent radical with a molecule of dissolved oxygen. The solvent radical appears as a result of photoreduction of chloride complexes of Cu(II). The radical complex has a band in the optical absorption spectrum with a maximum at 415–420 nm in ethanol and isopropanol. The rate of formation of this complex is determined mainly by the reaction of the radical of the matrix (R^.) with complexes of bivalent copper. The rate constant of this process in isopropanol at room temperature is (2–3)·10⁸ liters/ mole·sec. Disappearance of the radical complex Cu(I)...RO₂ ^. takes place in a reaction with complexes Cu²⁺ _solv and CuCl⁺ with a rate constant of 2.3·10⁷ liters/mole·sec at room temperature.Translated from Teoreticheskaya in iÉksperimental'naya Khimiya, Vol. 22, No. 1, pp. 39–44, January–February, 1986.     

Spectrophotometric study of the complexation of iodine with 1,7-diaza-15-crown-5 in chloroform solution

The complex formation reaction between iodine and 1,7-diaza-15-crown-5 (DA15C5) has been studied spectrophotometrically in chloroform at 25°C. The resulting 1:2 (DA15C5:I₂) molecular complex was formulated as (DA15C5...;I⁺)I ₃ ^– . The spectrophotometric results, as well as the conductivity measurements, revealed that the gradual release of triiodide ion from its contact ion paired form in the molecular complex into the solution is the rate determining step of the reaction. The rate constant was calculated ask=(8.8±0.2)×10^–3 min^–1. The formation constant of the molecular complex was evaluated from the computer fitting of the absorbance-mole ratio data as logK _f=6.89±0.09.     

Ligand exchange reaction of Zn(II)-acetylacetonate complex with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid

Ligand exchange reaction of Zn(II)-acetylacetonate complex (Zn-acac₂) with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid (H₂TPPS) has been investigated spectrophotometrically and radiometrically. The exchange reaction was observed by spectral change from H₂TPPS to Zn-TPPS or activity of⁶⁵Zn(acac)₂ extracted into the chloroform phase. The 2nd order rate constants (k ₂) for the exchange reaction at 70 °C and at pH 7.8 were found to be 32.8±2.3 and 31.2±3.2 M^–1·s^–1 from the spectrometric and radiotracer experiments, respectively. For the direct complexation of Zn(II) with H₂TPPS, a similar 2nd order rate constant (k=32.4±4.7 M^–1·s^–1) was obtained as that in the ligand exchange reaction. The activation energies (E) for the exchange and the formation of Zn-TPPS were found to be 69.3±0.2 and 69.4±0.2 kJ·mol^–1, respectively, in the temperature range from 40 to 70 °C.     

Rates of reactions of some aqueous free radicals with platinum-ammine complexes using pulse radiolysis

The fast reaction technique of pulse radiolysis in conjunction with UV- visible absorption detection was used to determine the rate of reactions of hydrated electron, hydrogen atom, hydroxyl radical and dichloride anion radical with tetraammineplatinum(II) perchlorate and with trans- dihydroxotetraammineplatinum(IV) perchlorate complexes. Generally these reactions proceed at near diffusion-controlled rates. The second-order rate constant for the reaction of e _aq ^– , H, OH and Cl ₂ ^– radical with the Pt(II) complex are (1.9±0.1)·10¹⁰ M^–1·s^–1, (2.8±0.3)·10¹⁰ M^–1·s^–1, (6.6±0.4)·10⁹ M^–1·s^–1 and (9±1)·10⁹ M^–1·s^–1, respectively. The rate constant for the reaction of e _aq ^– with the Pt(IV) complex is (4.9±0.3)·10¹⁰ M^–1·s^–1, however, H atom and OH radical reactions proceed at relatively slower rates.     

Determination of the formation rate constant of carrier-free111In(III) with EDTA

The kinetics of reaction of indium(III)ion with EDTA (H₄ edta) has been studied in aqueous acidic solutions using carrier-free¹¹¹In and low concentrations of EDTA. The reaction takes place predominatly between indium(III) and H₃ edta. The rate constant k₃ is determined to be k₃=(1.3±0.1)·10⁵ dm³ mol^–1 s^–1 (25 °C).     

Acid Catalysis in Reaction of Ozone with Chloride Ions

The kinetics of the interaction of ozone with aqueous solutions of chlorides resulting in Cl₂ evolution to the gas phase was studied. The reaction of O₃ with Cl^– is accelerated by H⁺ ions. The effects of the concentrations of H⁺ and Cl^–, the ionic strength, and temperature (ranged from 7 to 60°C) on the reaction rate were studied. A mechanism explaining the experimental kinetics was proposed. The acid catalysis is due to the formation of the HO₃Cl complex, which is in equilibrium with H⁺, O₃, and Cl^–. The constants of reactions involved in the proposed mechanism were determined.     

Experimental Evidence for Acceleration of Reaction between Iodine Monoxide and Chlorine Monoxide at the Reactor Surface

The reaction of iodine monoxide with chlorine monoxide resulting in atom escape to the gas phase is studied at T = (303 ± 5) K and P = 2.5 Torr using a flow setup for measuring the resonance fluorescence signals of atomic iodine and chlorine. The heterogeneous reaction between chlorine monoxide and iodine monoxide occurring at the reactor surface covered with an F32-L Teflon-like compound and treated by the reaction products is characterized by the rate constant k = (4.9 ± 0.2) × 10^–11 cm³ molecule^–1 s^–1. This value is substantially higher than the rate constant for the homogeneous reaction IO^· + ClO^· (k ₁ 1 × 10^–12 cm³ molecule^–1 s^–1).     

Comparative studies on hydrolysis of bis(p-nitrophenyl) phosphate catalyzed by short- and long-alkyl-multiamine metallomicelles

Four short- and long-alkyl-multiamine ligands L¹–L⁴ have been synthesized and characterized. The catalytic efficiency of complex CuL¹ and functional metallomicelles CuL²–CuL⁴ were comparatively investigated for the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in buffered solution at 30 °C. The ternary kinetic model for metallomicellar catalysis was suggested to analyze the experimental data. The kinetic and thermodynamic parameters k^′_N, K_T and pK_a were obtained. The results indicated that the complexes with 1:1 ratio of ligands L²–L⁴ to copper(II) ion were the kinetic active catalysts, and the deprotonized Cu(II) complex formed by activated water molecule was the real active species for BNPP catalytic hydrolysis. The real rate constant of the reaction catalyzed by CuL¹–CuL⁴ was 4.00 × 10⁻⁶, 7.44 × 10⁻⁵, 1.42 × 10⁻⁴ and 4.10 × 10⁻⁴ s⁻¹, respectively. The effects of ligand and microenvironment on the hydrolytic reaction of BNPP have been discussed in detail.     

A complex of buckminsterfullerene with sulfur,C60·2S8: synthesis and crystal structure

The C₆₀·2S₈ complex was prepared by reaction of buckminsterfullerene C₆₀ with sulfur in trichloroethylene and its single-crystal X-ray structure was studied at room temperature. Crystals of this compound are monoclinic, space groupC 2/c, a=20.90(1),b=21.10(1),c=10.537(9) Å, =111.29(7)°,Z=4,d _calc=1.89 g·cm^–3. The crystal structure of the C₆₀·2S₈ complex consists of packed fullerene molecules that form hexagonal channels along thec axis with eight-membered crown-shaped S₈ cyclic molecules inside the channels. The distances between the centers of neighboring fullerene molecules are 10.036(7), 10.636(7), and 10.537(9) Å. Each C₆₀ molecule is linked to eight S₈ molecules with ten shortened intermolecular contacts C...S 3.41(1)–3.52(2) Å. The average values of the C=C and C-C bond lengths are 1.32(3) and 1.47(3) Å, which attest to a significant degree of localization of electron density in the c₆₀ molecule.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 262–266, February, 1994.     

An independent kinetic and mechanistic study of the secondary reactions in the substitution of [FeL(OH)](n−2)− (L= triethylenetetraaminehexaacetic acid) by cyanide ions

Summary The kinetics of reaction between [Fe(CN)₅OH]^3– and CN^– have been investigated spectrophotometrically at pH=11.00, I=0.25 M(NaClO₄) and temp.=25.0°C by disappearance of the absorption peak at 395 nm. The rate data for this reaction followed first order kinetics in both [Fe(CN)₅OH^3–] and [CN^–]. The second order rate constant (k_f) was found to be (3.44±0.08)×10^–3 M^–1 s^–1. The pH dependence of the reaction was also investigated in the range 9–12. The activation parameters were found to be H=36.4kJ mol^–1 and S=–168JK^–1 mol^–1.The reaction between [Fe(CN)₆]^3– and TTHA^6– (TTHA=triethylenetetraaminehexaacetic acid) has also been followed spectrophotometrically at 420 nm, pH=11.00, I=0.1M (NaClO₄) and temp.=25.0°C. This reaction also followed first order kinetics in both [Fe(CN) ₆ ^3– ] and [TTHA^6–]. The second order rate constant (k_f) was found to be (3.74±0.21)×10^–2 M^–1 s^–1. The rate of reaction was found to increase with pH in the range 9–11.5. The different reactive species of TTHA (L) are H₂L^4– HL^5– and L^6–. The rate constants for these species have been calculated and the pH profile is explained. The values of the activation parameters were found to be H= 30.9 kJmol^–1 and S=–167JK^–1 mol^–1. Electron transfer from [Fe(CN)₆]^3– to the substrate followed by decomposition of the latter is proposed. The oxidation products of TTHA have been investigated by g.l.c.     

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.     

Kinetics of oxidation of hypophosphite ion by platinum(IV) in an alkaline medium

Summary The kinetics of the oxidation of hypophosphite ion by platinum(IV) have been studied spectrophotometrically in alkaline medium at different temperatures. The rate increases as the pH increases and the empirical rate law applicable to the reaction is given by:-d[Pt^IV]/dt = k₃[Pt^IV][H₂PO^2–][OH^–]The rate constant is 2.17×10^–3 (l² mo^–2s^–1) at 40.5°. The energy and entropy of activation for the reaction are 104.2 kJ mol^–1 and 28.5 JK^–1mol^–1 respectively.     

Utilization of Chromatographic and spectroscopic techniques to study the oxidation kinetics of selenomethionine

Ion-exchange LC and spectroscopic supporting techniques have been successfully used to study the kinetics and mechanism of oxidation reactions of selenomethionine (SeMet). Oxidation of selenomethionine with both cyanogen bromide (CNBr) and hydrogen peroxide (H₂O₂) proceeds through a stable intermediate which undergoes cyclization and C-Se bond cleavage to form 2-amino-4-butyrolactone. This stable intermediate was identified by IR spectroscopy as methionine dihydroxy selenide. The CH₃-Se moiety of SeMet formed methyl selenic acid upon reaction with H₂O₂ and methyl selenocyanate (CH₃SeCN), characterized by GC-MS, for the reaction with CNBr. Both reactions were of apparent first order with respect to the concentration of SeMet. A rate constant (k₁)of 4.0×10^–3 s^–1 for the reaction of SeMet with HO and 4.0×10^–3 s^–1 for the reaction with CNBr were determined at a temperature of 22°C. Oxidation of methionine (Met) gives disparate kinetics and oxidation products from SeMet. Thus the differential rate method can be utilized to quantitatively separate SeMet in biological samples in the presence of much higher concentrations of Met.     

Pulse radiolysis investigations on the reactions of primary radiolytic species of water with atropine

On pulse radiolysis of N₂O saturated aqueous solutions of atropine, an optical absorption band (_max at 320 nm,e=2.81·10³ dm³·mol^–1·cm^–1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·10⁸ dm³·mol^–1·s^–1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·10⁹ dm³·mol^–1·s^–1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e _aq ^– was found to react with atropine forming a transient band with _max at 310 nm (=3.55·10³ dm³·mol^–1). Its decay was also second order with a rate constant of 1.64·10⁹ dm³·mol^–1·s^–1. The bimolecular rate constant for the reaction of e _aq ^– with atropine as estimated from the decay of e _aq ^– absorption at 720 nm is 3.9·10⁹ dm³·mol^–1·s^–1. Specific one-electron oxidizing and reducing agents (such as Cl ₂ ^– , Tl²⁺, SO ₄ ^– and (CH₃)₂COH, CO ₂ ^– , respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e _aq ^– was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·10⁹ and 3.2·10⁹ dm³·mol^–1·s^–1, respectively.