Charge-transfer complexes betweenp-toluidine and iodine in solution: A kinetic study

The kinetics of charge-transfer interaction betweenp-toluidine and iodine in methylene chloride was investigated in depth. Thethermal process of formation of theinner complex was found to proceed to an equilibrium. Thephotochemical process follows a different reaction coordinate, going through the formation of an exciplex between the excitedouter complex and the amine ground state. In both cases the same ionic complex (Am ₂I⁺I ₃ ^– , whereAm stands forp-toluidine) was detected as the final product.

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Kinetische Untersuchung der Charge-Transfer-Komplexe zwischenp-Toluidin und Jod

Zusammenfassung Die Kinetik der Charge-Transfer-Wechselwirkung zwischenp-Toluidin und Jod in Methylenchlorid wurde ausführlich untersucht. Derthermische Prozeß, der zur Bildung desinner-Komplexes führt, geht bis zu einem Gleichgewicht. Derphotochemische Prozeß folgt einer unterschiedlichen Reaktionskoordinate und verläuft über die Bildung eines Exziplexes zwischen dem angeregtenouter-Komplex und dem Amin im Grundzustand. In beiden Fällen wurde derselbe ionische Komplex (Am ₂I⁺I ₃ ^– , wobeiAm fürp-Toluidin steht) als Endprodukt festgestellt.

     

Charge-transfer complexes in homogeneous catalysis

It is shown that these complexes can be formed between the reactants in redox reactions. Oxidizing and reducing agents are classified on the basis of charge-transfer capacity, which is defined by the integral for the overlap between the filled orbital of the reductant and the free one of the oxidant. Unfilled diffuse d-orbitals most readily give such complexes. Homogeneous catalysis of a redox reaction involves charge transfer in either direction between the catalyst (which has partly filled d-orbitals) and one of the reagents. The transfer is very much dependent on the orientation, so activators play a large part.     

A voltammetric study of aquozinc(II) complexes in methanol

Results of chronopotentiometric and polarographic determinations of the formation constants of aquozinc(II) complexes in methanol are reported. Chronopotentiometry offers some advantages over polarographic and spectrophotometric methods for studies of this kind.     

Charge-transfer complexes of barbiturates and phenytoin

Simple and sensitive spectrophotometric methods are described, for the first time, for the determination of sodium salts of phenobarbital (1), thiopental (2), methohexital (3) and phenytoin (4). The methods are based on the reaction of these drugs as n-electron donors with the sigma-acceptor iodine and various pi-acceptors: 7,7,8,8-tetracyanoquinodimethane; 2,3-dichloro-5,6-dicyano-1,4-benzoquinone; 2,3,5,6-tetrachloro-1,4-benzoquinone; 2,3,5,6-tetrafluoro-1,4-benzoquinone; 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone; tetracyanoethylene and 2,4,7-trinitro-9-fluorenon. Depending on the solvent polarity, different coloured charge-transfer complexes and radicals were developed. Different variables and parameters affecting the reactions were studied and optimized. The formed complexes were examined by UV/VIS, infrared and (1)H-NMR. Due to the rapid development of colours at ambient temperature, the obtained results were used on thin layer chromatograms for the detection of the investigated compounds. Beer's plots were obeyed in a general concentration range of 1-400 mug ml(-1) for the investigated compounds with different acceptors. Interference from some co-formulated drugs was also studied. No interference was observed due to additives commonly present in the pharmaceutical preparations. The proposed methods could be applied successfully to the determination of the investigated compounds in pure and pharmaceutical dosage forms with good accuracy and precision, the recoveries ranged from 98.7+/-0.5 to 101.1+/-0.5%. The results were compared favourably with the official methods.     

A spectrophotometric and thermodynamic study of the charge-transfer complexes of iodine with 2-aminomethyl-15-crown-5 in chloroform and 1,2-dichloroethane solutions

Interaction of 2-aminomethyl-15-crown-5 (AM15C5) with iodine has been investigated spectrophotometrically in chloroform and 1,2-dichloroethane (1,2-DCE) solutions. The observed time dependence of the charge-transfer band and subsequent formation of I(3)(-) in solution were related to the slow transformation of the initially formed 1:1 AM15C5.I(2) outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants were evaluated from the absorbance- and conductivity-time data. The stoichiometry and formation constants of the resulting EDA complexes have also been determined. Thermodynamic parameters, Delta H degrees and Delta S degrees , of the complexes have been determined from the temperature dependence of stability constants by Van't Hoff equation. The results indicate that iodine complexes of AM15C5 in both solvents are enthalpy stabilized but entropy destabilized. The influence of solvent properties on the kinetics and stability of the resulting charge-transfer complexes are discussed.     

Copper(II) complexes of N-(phosphonomethyl)glycine in aqueous solution: a thermodynamic and spectrophotometric study

Copper(II) complexes with the herbicide N-(phosphonomethyl)glycine (glyphosate) have been investigated in aqueous solution by means of pH-metric measurements at different temperatures, 5 相似文献   

A study of HPLC separation and spectrophotometric, polarographic and voltammetric detection of 4-substituted derivatives of N-nitroso-N-methylaniline

Optimised conditions have been found for the separation of N-nitroso-N-methylaniline derivatives substituted in the position 4 (4-R-NMA, where R =- H,- CH₃, - OCH₃, - Cl, - CN, - OH and - NO₂), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of aqueous 0.01 mol l^–1 KH₂PO₄ with methanol (4+6) or acetonitrile (7+3), or a mixture of water, methanol, acetonitrile and 80% H₃PO₄ (200+200+200+3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hanging mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photolytic denitrosation of the analytes. The UV photometry is the most universal and yields limits of detection around 10^–6 mol l^–1. Polarography exhibits the poorest sensitivity (with a limit of detection of ca. 10^–5 mol l^–1) but it can be used for selective detection of 4-NO₂-NMA. Direct voltammetric detection is selective for the oxidizable derivatives and the limits of detection attained are lower than those obtained by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH₃-NMA). When the analytes are photolytically denitrosated to yield oxidizable derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH₃-NMA and 4-NO₂-NMA has limits of detection one order of magnitude lower than those obtained UV photometrically.     

Charge-transfer intensity in complexes with symmetrically equivalent acceptors

Mulliken's model for the intensity of charge-transfer absorption bands in donor/acceptor complexes is extended to transition-metal compounds. Attention is focused on the analysis of systems containing a central metal ion and symmetrically equivalent π-acceptor ligands. The theory is illustrated for a one-donor/two-acceptor complex in D_2d point symmetry. Results are stated for symmetries of commonly occurring transition-metal compounds that display well-documented metal-to-ligand charge-transfer transitions.     

Charge-transfer complexes of cobaltocene and nickelocene with tetrachloromethane

The photochemical properties of the systems cobaltocene—tetrachloromethane and nickelocene—tetrachloromethane in ethanol and cyclohexane were investigated; the equilibrium constants and molar extinction coefficients of the donor—acceptor complexes in these systems were determined.

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Charge-Transfer Komplexe von Kobaltocen und Nickelocen mit Tetrachlorkohlenstoff

Zusammenfassung Es wurden die photochemischen Eigenschaften der Systeme Kobaltocen–CCl₄ und Nickelocen–CCl₄ in Ethanol und Cyclohexen als Lösungsmittel untersucht. Die Gleichgewichtskonstanten und die molaren Extinctionskoeffizienten der Donor—Acceptor-Komplexe in diesen Systemen wurden bestimmt.

     

Charge-transfer properties of the hydrogen bond: Part 6. Charge-transfer theory and dipole moments of hydrogen-bonded complexes

The enhancement of the dipole moments of hydrogen-bonded complexes are discussed using Mulliken's charge-transfer theory.A linear relation is found between the ratio a/b and the ionization potential of the donor, I^V_D. This behaviour is similar to that previously found for halogen charge-transfer complexes [6].     

Charge-transfer complexes from decamethylferrocene and 1,4-quinone derivatives: neutral-ionic phase diagrams for metallocene complexes

Charge-transfer (CT) complexes of ferrocenes with 1,4-quinone derivatives were investigated. Deca- and octamethylferrocene complexes with 1,4-naphthoquinone derivatives were prepared and structurally characterized; these were neutral 1:2 DA complexes with mixed-stack structures. The formation of complexes with 1,4-benzoquinones was examined by applying solvent-drop grinding. CT energies and phase transitions in these neutral and other ionic complexes were investigated. Their electronic states are discussed on the basis of the phase diagrams derived for mixed-stack ferrocene-based CT complexes, taking into account their dependence on the DA ratio, dimensionality, and intermolecular interactions.     

Tungsten(VI) complexes formed in an excess of gluconic acid: A polarimetric and spectrophotometric study

Summary The tungsten(VI)-gluconic acid system in an excess of this organic reagent has been spectroscopically and polarimetrically studied and four species, two mononuclear with stoichiometry 12 (metalligand) and two dinuclear with composition 22, have been identified. The non-formation of a binuclear species with stoichiometry 21 (metalligand) demonstrates some preference towards coordination of carboxylate group.The pH of the medium is the main variable controlling the formation and interconversion equilibria, which are similar to those previously described for other -hydroxyacids ligands. Thus, the three species being stable at a lower pH require for their formation from [WO₄]^2– and gluconate ions, 2,2 and 2.5H⁺/W, respectively.However, for pH values higher than 9.0, where the carboxylic group may be assumed not to coordinate, a fourth weaker monomeric complex is formed, similar to those formed by mannitol or sorbitol at the same pH.     

A potentiometric and spectrophotometric study on acid-base equilibria in ethanol-aqueous solution of acetazolamide and related compounds

Acid-base equilibria in ethanol-aqueous solution of 5-acetamido-1,3,4-thiadiazole-2-sulfonamide (acetazolamide, H(2)acm), 5-tertbutyloxycarbonylamido-1,3,4-thiadiazole-2-sulfonamide (B-H(2)ats), 5-amino-1,3,4-thiadiazole-2-sulfonamide (Hats) and 5-amino-1,3,4-thiadiazole-2-thiol (Hatm) at 25 degrees C, 0.15 mol dm(-3) ionic strength (NaNO(3)), have been investigated by potentiometry and UV spectrophotometry. The ionization constants were calculated with SUPERQUAD program from potentiometric measurements and by a method according to Edsall et al. using the mole fractions determined by complementary tri-stimulus colorimetry (CTS). The constants obtained by potentiometry were: B-H(2)ats, pk(a(1))=7.33(3) and pk(a(2))=9.27(1); Hats, pk(a(1))=2.51(3) and pk(a(2))=8.49(1); Hatm, pk(a(1))=1.92(1) and pk(a(2))=6.81(1); whereas the constants determined by spectrophotometry were: H(2)acm, pk(a(1))=7.78(1) and pk(a(2))=9.57(2); B-H(2)ats, pk(a(1))=7.71(2) and pk(a(2))=9.61(2); Hats, pk(a(1))=2.19(3) and pk(a(2))=8.61(2); Hatm, pk(a(2))=6.90(2). Theoretical calculations using MO semiempirical and ab-initio RHF/6-31G* computations for the compounds were also performed. It was possible to clarify the preferred deprotonation mechanism of acetazolamide and B-H(2)ats in which the first deprotonation takes place at the carbonamido group.     

The thorium-apans complex : A spectrophotometric study

The compound formed from thorium and Apans has been studied by spectrophotometric methods and shown to contain thorium and reagent in the ratio 1 : 2. The apparent stability constant of this complex has been measured as 1.4 ± 0.1$\text{.}\text{?}$10¹⁰     

阻抑动力学光度法测定乳品中的痕量碘

研究了在稀H2SO4介质中,痕量I-对KBrO3氧化酸性品红的阻抑作用及其动力学条件,建立了测定痕量I-的阻抑动力学光度分析的新方法.测定I-的线性范围为0～0.04 μg/mL,检出限为1.1×10-9 g/mL.已用于乳品中痕量碘的测定.     

Charge-transfer complexes in organic chemistry—XII : Solvent effects on charge-transfer spectra

The charge-transfer transition energies of 2,6-dimethoxynaphthalene and 9-methylanthracene with tetrachlorophthalic anhydride, and acenaphthene and anthracene with 3,5-dinitrophthalic anhydride were measured in sixty aprotic solvents. The observed effects can be interpreted in terms of various solvent parameters if the solvents are divided into the following classes: halogen-containing, aromatic and n-donor solvents.