Studies on the Photochemical Oxidation of 1,3-Diphenylisobenzofuran and Cis-Cyclooctene in N,N-Dimethylformamide–Propanol Binary Mixture

Kinetic studies on the photochemical oxidation of 1,3-diphenylisobenzofuran have been carried out in binary liquid mixtures of N,N-dimethylformamide (DMF) with 1-propanol (PrOH). The strongest influence of solvating effects upon the course of this reaction was observed for compositions of the studied mixture corresponding respectively to ca. 50?mol% of PrOH. Additionally, we have carried out analogous studies of photooxidation of cis-cyclooctene. Similarly as previously, the noticeable influence of solvating effects upon the course of this reaction corresponded to ca. 50?mol% of DMF. We suspect that the mechanism of this effect is associated with the formation of the polar intermediate during the ene reaction being easier.     

Spectral and Mechanistic Investigation of the Osmium(VIII) Catalyzed Oxidation of Diclofenac Sodium by the Copper(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of the osmium(VIII) (Os(VIII)) catalyzed oxidation of diclofenac sodium (DFS) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium has been studied spectrophotometrically at a constant ionic strength of 1.0 mol⋅dm⁻³. The reaction showed first order kinetics in [Os(VIII)] and [DPC] and less than unit order with respect to [DFS] and [alkali]. The rate decreased with increase in [periodate]. The reaction between DFS and DPC in alkaline medium exhibits 1:2 [DFS]:[DPC] stoichiometry. However, the order in [DFS] and [OH⁻] changes from first order to zero order as their concentration increases. Changes in the ionic strength and dielectric constant did not affect the rate of reaction. The oxidation products were identified by LC-ESI-MS, NMR, and IR spectroscopic studies. A possible mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The catalytic constant (K _C) was also calculated for Os(VIII) catalysis at the studied temperatures. From plots of log ₁₀ K _C versus 1/T, values of activation parameters have been evaluated with respect to the catalytic reaction. The activation parameters with respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined. The active osmium(VIII) and copper(III) periodate species have been identified.     

Kinetic studies on the reaction of N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetate chromium(III) with hydrogen peroxide

The rate of reaction of Cr(III)L (L=N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetate) with hydrogen peroxide was studied in aqueous media and was found to yield Cr(VI) over the temperature range of 25–41 °C. The reaction was followed spectrophotometrically at 396 nm under pseudo-first order conditions with hydrogen peroxide in a large excess. The reaction follows first-order kinetics in Cr(III). The dependence of the rate constant on hydrogen peroxide concentration is attributed to the formation of an intermediate between the monohydroxy chromium(III) complex and hydrogen peroxide which decomposes in the rate determining step. At high hydrogen peroxide concentration, the order is changed from first to zero order.The values of the intramolecular electron transfer rate constant, the formation constant of the intermediate complex and the activation parameters were calculated.     

Oxidation of Fursemide by Diperiodatocuprate(III) in Aqueous Alkaline Medium—a Kinetic Study

Fursemide is the chemical compound 4-chloro-2-(furan-2-ylmethylamino)-5-(aminosulfonyl) benzoic acid. It was oxidized by diperiodatocuprate(III) in alkali solutions, and the oxidation products were identified as furfuraldehyde and 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid. The reaction kinetics were studied spectrophotometrically. The reaction was observed to be first order in [oxidant] and fractional order each in [fursemide] and [periodate], whereas added alkali retarded the rate of reaction. The reactive form of the oxidant was inferred to be [Cu(H₃IO₆)₂]⁻. A mechanism consistent with the experimental results was proposed, in which oxidant interacts with the substrate to give a complex as a pre-equilibrium state. This complex decomposed in a slow step to give a free radical that was further oxidized by reaction with another molecule of DPC to yield 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid and furfuraldehyde in a fast step. This reaction was studied at 25, 30, 35, 40 and 45 °C, and the activation parameters E _a,ΔH ^#,ΔS ^# and ΔG ^# were determined to be 51 kJ⋅mol⁻¹,48.5 kJ⋅mol⁻¹,−63.5 J⋅K⁻¹⋅mol⁻¹ and 67 kJ⋅mol⁻¹, respectively. The value of log ₁₀ A was calculated to be 6.8.     

The Effect of Temperature on the Equivalent Conductivities and Ion-Association Constants of Some Tris-(ethylenediamine)chromium(III) Complexes in N,N-dimethylformamide and N,N-dimethylacetamide

The equivalent conductivities of tris-(ethylenediamine)chromium complexes, [Cr(en)₃]X₃ (where X⁻= Cl⁻, Br⁻, I⁻; en = ethylenediamine) were measured as functions of temperature (278.15 to 328.15 K) and concentration [(1.948 ×10⁻⁴ to 10.728 ×10⁻⁴ mol⋅dm⁻³) and (2.282 ×10⁻⁴ to 11.246 ×10⁻⁴ mol⋅dm⁻³)] in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC), respectively. Equivalent conductivity values for [Cr(en)₃]X₃ in DMF were found to be higher than those in DMAC. The conductivity data were analyzed with the Robinson-Stokes equations. For [Cr(en)₃]X₃, the limiting equivalent ionic conductivities of [Cr(en)₃]³⁺ and the ion-association constants (K _A) of the ion-pair between [Cr(en)₃]³⁺ and the monovalent halide anions were determined in DMF and DMAC. The values of K _A for three complex salts in DMF were higher than those in DMAC. This can be ascribed to an increase of the ion-association constants with a decrease of the relative permittivity of the solvents. The values of K _A at 298.15 K decreased in the order Cl⁻> Br⁻> I⁻ in DMF and Cl⁻> I⁻> Br⁻ in DMAC. The K _A values for [Cr(en)₃]Cl₃ increased with increasing temperature in both DMF and DMAC. For [Cr(en)₃]X₃(X⁻= Br⁻, I⁻) in both solvents, this indicates increasing disorder occurs with increasing temperature. Thermodynamic parameters (standard Gibbs energy, enthalpy and entropy changes) were determined from the temperature dependence of K _A in DMF and DMAC. These parameters were inter-compared in their dependences on temperature and solvent.     

Volumetric Properties of l-Alanine and l-Serine in Aqueous N,N-Dimethylformamide Solutions at 298.15 K

The densities of l-alanine and l-serine in aqueous solutions of N,N-dimethylformamide (DMF) have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes $ (V_{\phi } ) $ ( V ? ) , standard partial molar volumes $ (V_{\phi }^{0} ) $ ( V ? 0 ) , standard partial molar volumes of transfer $ (\Updelta_{\text{tr}} V_{\phi }^{0} ) $ ( Δ tr V ? 0 ) and hydration numbers have been determined for the amino acids. The $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 values of l-serine are positive which suggest that hydrophilic–hydrophilic interactions between l-serine and DMF are predominant. The –CH₃ group of l-alanine has much more influence on the volumetric properties and the $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 have smaller negative values. The results have been interpreted in terms of the cosphere overlap model.     

Dissociation Constant of Acetic Acid in (N,N-Dimethylformamide + Water) Mixtures at the Temperature 298.15 K

In the present work the thermodynamic dissociation constants of acetic acid were determined in (N,N-dimethylformamide (DMF) + water) mixtures over the DMF mole fraction range from 0 to 0.65 at the temperature 298.15 K by the potentiometric titration method. The dissociation constant in pure DMF was obtained by extrapolation and comparative calculation methods. The dependence of the acetic acid dissociation constant on the mixed solvent composition was fitted with linear multiple regression of the solvatochromic parameters of (DMF + water) mixtures at every studied composition.     

Static Dielectric Constants and Kirkwood Correlation Factor of the Binary Mixtures of N-Methylformamide with Formamide,N,N-Dimethylformamide and N,N-Dimethylacetamide

Static dielectric constant values of the binary mixtures of N-methylformamide with formamide, N,N-dimethylformamide and N,N-dimethylacetamide have been measured in the whole composition range at 303 K. The Kirkwood correlation factor values of the amide–amide mixtures were determined from the measured values of the static dielectric constant and high-frequency limit dielectric constant. The evaluated values of the excess dielectric constant and deviation in the Kirkwood correlation factor infer that deviations of their mixture values occur from the mole-fraction mixture law. Results confirm that there are strong hydrogen-bond interactions between unlike molecules of amide–amide mixtures and that 1:1 complexes are formed.     

Electrochemical investigation of N,N′-Propylene-bis-(salicylideneiminato) Mn(III) in phosphate buffer solutions

Summary An electrochemical study on N,N-Propylene-bis-(salicylideneiminato) Mn(III) was performed using cyclic voltammetry with convolution-deconvolution and digital simulation in phosphate buffer solutions ofpH values ranging from 5–9.5 at a hanging mercury drop electrode (HMDE). The reduction pathway of the investigated complex shows that a moderately fast transfer of one electron is followed by a very fast chemical reaction (E _q C _irr scheme). The electrochemical parameters have been determined experimentally andvia digital simulation experiments.

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Elektrochemische Untersuchung von N,N-Propylen-bis-(salicylideniminato)-Mn(III) in Phosphatpufferlösungen

Zusammenfassung N,N-Propylen-bis-(salicylideniminato)-Mn(III) wurde in Phosphatpufferlösungen mitpH-Werten im Bereich von 5–9.5 an einer Quecksilbertrofelektrode (HMDE) mittels cyclischer Voltammetrie (Konvolution-Dekonvolution, digitale Simulation) elektrochemisch untersucht. Ein mäßig schneller Transfer eines Elektrons wird von einer sehr schnellen chemischen Reaktion gefolgt (E _q C _irr-Schema). Die elektrochemischen Parameter wurden experimentell und durch Simulations-experimente bestimmt.

     

Study on the Mechanism of the Radiation-Induced Chain Oxidation of N,N,N,N-Tetramethyl-4,4′-diaminodiphenylmethane by Tetrabromomethane in Poly(vinyl chloride) Films

Kinetics and mechanism of the radiation-induced chain oxidation of N,N,N,N-tetramethyl-4,4-diaminodiphenylmethane (Am) by tetrabromomethane in poly(vinyl chloride) (PVC) films were studied by ESR and optical spectroscopy. The quantitative analysis of the ESR spectra of PVC films containing Am and CBr₄ irradiated with -rays at 77 K was performed. The nature of radical species involved in the chain process was established. It was shown that the heating of the films after their irradiation at 77 K resulted in the formation of free radicals Am^·, which initiated the chain oxidation of amine with a chain length of 100. The kinetic features of the chain oxidation–reduction reactions occurring in vacuum and in the presence of oxygen were compared.     

Investigation of the kinetics of formation of 1 : 1 complex between chromium(III) with 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate ion in aqueous acidic media

The kinetics of formation of the 1?:?1 complex of chromium(III) with 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate (1,3-pddadp) were followed spectrophotometrically at λ _max?=?557?nm. The reaction was first-order in chromium(III). Increasing the 1,3-pddadp concentration from 2.2?×?10^?2 to 0.11?mol?dm^?3 accelerated the reaction rate. Increasing the hydrogen ion concentration from 1.995?×?10^?5 to 6.31?×?10^?4 mol?dm^?3 retarded the reaction rate. The reaction rate was also retarded by increasing ionic strength and dielectric constant of the reaction medium. A mechanism was suggested to account for the results obtained which involves ion-pair formation between the various reactants. Values of 22?kJ?mol^?1 and ?115?J?K^?1 mol^?1 were obtained for the energy and the entropy of activation, respectively, which indicate an associative mechanism. The logarithm of the formation constant of the 1?:?1 complex formed was 11.3.     

Cyclization of N,N′‐Bis(Salicylidene)Diamines with Carbon Suboxide

Abstract

The reaction between N,N′‐bis(salicylidene)diamines and carbon suboxide afforded dicoumarinoyl diamides in only one step and in yields that strictly depend on the methylene linkers between the salicylic moieties.     

Bis(arene)metal compounds: I. Nucleophilic substitution of bis(η6-chlorobenzo-trifluoride)chromium(0) with thiophenoxide

The ortho, meta and para complexes of bis(η⁶-chlorobenzotrifluoride)chromium(0) were made by metal-vapor synthesis. Nucleophilic substitutions by thiophenoxide of these complexes are compared to nucleophilic substitutions by thiophenoxide on the uncoordinated arenes. It was found that substitution at the chloro position is more facile on the complexes than on the free arenes. Substitution of the chloro on the meta-isomer sandwich was more facile than substitution of the chloro on the ortho-isomer sandwich, contrary to the observed reactivity pattern in the free arenes.     

Ferrocene-containing ligands in the self-assembly of trinuclear μ3-oxocentered carboxylate complexes of chromium(III, III, III)carboxylate complexes of chromium(III, III, III)

New trinuclear μ₃-oxocentered chromium(III, III, III) complexes were obtained by the self-assembly of ferrocenecarboxylate ligands and the Cr₃O fragment. The complexes were investigated by fast-atom bombardment (FAB) mass spectrometry, cyclic voltammetry, and electronic and IR spectroscopy. V. I. Vernadskii Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine, 32/34 Prospekt Akademika Vernadskogo, Kiev 03142, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 4, pp. 233–237, July–August, 2000.     

Linear/branched Block Polyethylene Produced by α-Diimine Nickel(Ⅱ)Catalyst and Bis(phenoxy-imine) Zirconium Binary Catalyst System in the Presence of Diethyl Zinc

In order to promote development of linear/branched block polyethylenes based on new catalytic systems,we synthesized a novel α-diimine nickel(Ⅱ) complex with isopropyl substituents on ortho-N-aryl and hydroxymethyl phenyl substituents on para-N-aryl structures.The activity of α-diimine nickel(Ⅱ) catalyst was 3.02×106 g·molNi-1·h-1 at 70 ℃,and resultant polyethylene possessed 135/1000C branches.The linear/branched block polyethylenes were synthesized from ethylene polymerization catalyzed by the α-diimine nickel(Ⅱ) complex/bis(phenoxy-imine) zirconium in the presence of diethyl zinc.With the addition of ZnEt2 (from 0 to 400),the melting peak of resultant polyethylene changed from a single melting peak to bimodal melting peaks.The molecular weights of resultant polyethylene ranging from 26.8 kg/mol to 17.1 kg/mol and PDI values varying gradually from 24.4 to 15.2 were obtained via adjusting ZnEt2 equiv.and molar ratio of two catalysts.In addition,the branching degree of the polyethylene increased from 13/1000C to 56/1000C with the increase of the proportion of α-diimine nickel(Ⅱ) catalyst.Using this binary catalyst system,the reaction temperature of chain shuttling polymerization can be carried out at 70 ℃,which is more conducive to industrial application.     

Synthesis,crystal structure and reactivity of trans-diaquo N,N′-ethylenebis-(3-methoxysalicylideneiminato)chromium(III)

A new chromium(III) Schiff base complex, [Cr(3-methoxysalen)(H₂O)₂]ClO₄, where salen=N,N-ethylenebis- (salicylideneimine), has been synthesized and characterized by spectroscopic techniques. Single crystal X-ray data reveals that the complex assumes a trans-diaquo structure with formulation [Cr(C₁₈H₂₂N₂O₆)]ClO₄ but, unlike in Cr (salen)(H₂O)₂ ⁺, the two trans-water molecules are equidistant from Cr^III. The effect of the substituent on the phenyl ring in respect of redox reactivity has been investigated. The kinetics of the oxidation of [Cr(Schiff base)- (H₂O)₂]ClO₄, where Schiff base=salen, (1) and 3-OMe-salen, (2) by PhOI has been studied. The bimolecular rate constant for the formation of the O=Cr^v Schiff base in case of (2) was four times faster than that of (1). The introduction of the OMe group substituent on the phenyl ring influences not only the structure and crystal packing, but also the reactivity of the complex and the electronic environment around the metal ion.     

Electrochemical synthesis and spectroscopy of the polymeric form of N,N′-bis(3-methoxysalicylidene)-1,3-propylenediamine

Electrochemical oxidation of N,N′-bis(3-methoxysalicylidene)-1,3-propylenediamine leads to the formation of a conducting polymer on the electrode surface. The diffusion coefficient and activation barrier of the charge transfer in the bulk of the polymer in an electrolyte medium were determined. The Schiff base and its polymeric form in the oxidized and reduced states were characterized by IR, X-ray photoelectron, and electronic absorption spectroscopy. Reversible changes in the polymer structure, accompanying its electrochemical oxidation-reduction, are substantiated.     

(η6-Anisole) (η2-benzene) dicarbonylchromium(0): an intermediate in the photochemical carbonyl substitution of (η6-anisole)tricarbonylchromium(0) in benzene

The photochemical carbonyl substitution of (η⁶-anisole)Cr(CO)₃ has been investigated by laser flash photolysis. Both transient spectra and second-order rate constants for the reactions of transients with nucleophiles are found to be extremely variable depending upon solvents used. The coordination of benzene to the transient in cyclohexane forms the transient in benzene, indicating two discrete chemical species: (η⁶-anisole)Cr(CO)₂ and (η⁶-anisole)Cr(CO)₂(η²-benzene). The latter type of transient was observed also for fluorobenzene and mesitylene, leading to the assignment of a weak band in the visible region as η²-arene → Cr charge transfer. The existence of (η⁶-arene)Cr(CO)₂(η²-arene′) may throw light on what have been described as solvent effects in organometallic reactions.     

Electrical Conductivity and Decomposition Potentials of the LiAsF6 Solutions in the Propylene Carbonate–N,N-Dimethylformamide Mixed Solvent

Russian Journal of Electrochemistry - The electrical conductivity of LiAsF6 solutions in a propylene carbonate–N,N-dimethylformamide mixed solvent is measured at temperatures of 253.15,...     

Comparison of the Activities of Pd(0) and Pd(I) in Low-Temperature Oxidation of Carbon Monoxide on the Pd/γ-Al2O3 Catalyst

Kinetics and Catalysis - Low-temperature oxidation of carbon monoxide on the Pd/γ-Al2O3 catalyst has been studied at room temperature and atmospheric pressure of air containing 100 mg/m3 CO....