Potential response in the uncatalyzed bromate oscillatory system

The potential response of the platinum indicator electrode in the uncatalyzed bromate oscillator (UBO) with three different substrates, namely gallic acid (GA), pyrogallol (PG) and veratraldehyde (VA) has been analyzed. The large amplitude oscillations obtained with a Pt electrode are due to the sequential response of the indicator electrode to the varying concentration ratios of the redox couples present in the reaction mixture.     

笼形聚偕氨肟树脂的研究──Ag(Ⅰ)在树脂上的吸附过程

测定了Ag+离子在笼形聚偕胺肟树脂（CAO）及其酸、碱处理产物（ACAO、BCAO）上的吸附容量．Ag+离子在BCAO树脂上吸附容量较高,但同非选择性吸附,在ACAO上的吸附容量则与处理树脂的酸的pKa值有关．用高pKa值的硼酸、苯酸和对氨基酚处理所得的ACAO树脂的吸附容量接近BCAO树脂的水平,认为是胶后胺肟基发生互变异构所致．吸附动力学表明Ag+离子在H3BO3/ACAO和C6H5OH/ACAO树脂上进行多层吸附．在吸附中伴随有氧化还原反应并生成Ag（O）微晶的过程．     

CoTPP电化学催化原溴代环己烷的机理

以电化学循环伏安、现场ＥＳＲ电化学以及现场薄层电化学方法研究了电生Ｃｏ（Ｉ）ＴＰＰ与溴代五己烷的反机制。在ＤＭＦ中，Ｃｏ（Ⅱ）／Ｃｏ（Ⅰ）的氧化还原有明显的催化溴代环己烷还原的特片，反现场有自由基生成，反应产物之一是Ｃｏ－Ｃ键化合物，可以在１．３０Ｖ（ＳＣＥ）－电子还原，当存在ＣＨ２－ＣＨＣＮ时，。生成另一种Ｃｏ－Ｃ键化合物，该化合物在－１．１０Ｖ（ＳＣＥ）处一电子还原，证明溴代环己烷与Ｃｏ（Ｉ）     

Highly sensitive catalytic determination of molybdenum

A novel, highly sensitive, selective, and simple kinetic method was developed for the determination of Mo(VI) based on its catalytic effect on the oxidation of 1-amino-2-naphthol-4-sulfonic acid (ANSA) with H₂O₂. The reaction was followed spectrophotometrically by tracing the oxidized product at 465 nm after 30 min of mixing the reagents. The optimum reaction conditions were: 10 mmol l⁻¹ ANSA, 50 mmol l⁻¹ H₂O₂, 100 mmol l⁻¹ acetate buffer of pH 5.0 ± 0.05 and at 40 °C. Addition of 200 μg ml⁻¹ diethylenetriaminepentaacetic acid (DTPA) conferred high selectivity for the proposed method. Following the recommended procedure, Mo(VI) could be determined with a linear calibration graph up to 2.5 ng ml⁻¹ and a detection limit, based on the 3S_b-criterion, of 0.027 ng ml⁻¹. The unique sensitivity and selectivity of the implemented method allowed its direct application to the determination of Mo(VI) in natural and industrial waste water. The method was validated by comparison with the standard ETAAS method. Moreover, published catalytic-spectrophotometric methods for the determination of molybdenum were reviewed.     

On the Role Played by Dimers of Radical Cations in the Process of Electrochemical Oxidation–Reduction of Polyaniline: The Data that Were Obtained Using the Method of Cyclic Voltabsorptometry in the Presence of Counteranions of a Diverse Nature

The electrochemical oxidation–reduction of films of polyaniline is studied in the presence of various counteranions. The differential cyclic voltabsorptometric (DCVA) curves (dA/dt relative to potential, where A is the optical absorption) are recorded at characteristic wavelengths corresponding to individual spectrum components previously isolated with the Alentsev–Fok method. The DCVA curves for aqueous solutions of HCl, HClO₄, and H₂SO₄ at different potential scan rates are compared to traditional cyclic voltammograms. For the DCVA curves obtained at 665 nm discovered is one broad peak of dA/dt in the region of potentials between the first and second stages of polyaniline oxidation (0.6 V vs. Ag/AgCl). An assumption is made about a chemical nature of the process of generation of absorption in this spectral region, which, more likely than not, is connected with the emergence of dimers of radical cations of polyaniline. It is discovered that the electrochemical processes in the region of potentials that correspond to the first stage of oxidation give rise to variations in the absorption inside several regions of spectrum: 435 nm (radical cations) and 755 nm (localized polarons). An assumption is made that the first peak of the current corresponds to several successive processes that occur in a polyaniline molecule in the course of oxidation as well as to the existence of heterogeneous regions where the generation of localized polarons proceeds at different rates.     

Redox polymerization of 2-hydroxyethyl methacrylate (HEMA). I. Influence of surfactants on polymerization kinetics

Oxidation of ferrous orthophenanthroline (FeP) by peroxydiphosphate (PP) in aqueous medium at pH 1 was followed spectrophotometrically. Kinetic analysis has shown that oxidation occurs via the formation of an intermediate complex between FeP and PP. Equi-librium and rate constants were calculated. Influence of surfactants on the oxidation of FeP by PP was also Investigated. The equilibrium constant for complex formation was found to be higher in the presence of surfactants. The enhanced complex formation has been attributed to the ionic interactions between the charged surfactant and the ionic species in the reaction medium. Polymerization of HEMA initiated by the redox system,FeP/PP, was carried out in aqueous medium, under the conditions of excess reductant over oxidant and excess oxidant over reductant. The polymerization followed different mech-anisms under these conditions; with excess oxidant, the growing polymer radicals underwent oxidative termination, while with excess reductant, primary radical termination was pre-ferred. The effect of surfactants on the aqueous polymerization of HEMA using the redox system FeP/PP was also investigated. In addition to the decrease in rate, the polymerization followed a different mechanism in the presence of surfactants, the growing radicals ter-minated by mutual interaction. © 1995 John Wiley & Sons, Inc.     

Electronic structural changes between nickel(II)-semiquinonato and nickel(III)-catecholato states driven by chemical and physical perturbation

The selective synthesis of tetracoordinate square-planar low-spin nickel(II)-semiquinonato (Ni(II)-SQ) and nickel(III)-catecholato (Ni(III)-Cat) complexes, 1 and 2, respectively, was achieved by using bidentate ligands with modulated nitrogen-donor ability to the nickel ion. The electronic structures of 1 and 2 were revealed by XPS and EPR measurements. The absorption spectra of 1 and 2 in a noncoordinating solvent, dichloromethane (CH2Cl2), are completely different from those in tetrahydrofuran (THF), being a coordinating solvent. As expected from this result, the gradual addition of N,N-dimethylformamide (DMF), which is also a coordinating solvent like THF, into a solution of 1 or 2 in CH2Cl2 leads to color changes from blue (for 1) and brown (for 2) to light green, which is the same color observed for solutions of 1 or 2 in THF. Furthermore, the same color changes are induced by varying the temperature. Such spectral changes are attributable to the transformation from square-planar low-spin Ni(II)-SQ and Ni(III)-Cat complexes to octahedral high-spin Ni(II)-SQ ones, caused by the coordination of two solvent molecules to the nickel ion.     

Synthesis and properties of bis(heteroazulen-3-yl)methyl cations and bis(heteroazulen-3-yl)ketones

The synthesis and properties of a novel type of bis(heteroazulen-3-yl)methyl cations, bis(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl cation salt and nitrogen analogues, (9a-c·PF₆⁻) and (9a-c·BF₄⁻), as well as bis(heteroazulen-3-yl)ketones (12a-d) are studied. The synthetic method was based on a TFA-catalyzed electrophilic aromatic substitution on the heteroazulenes (6a-d) with paraformaldehyde to afford the corresponding disubstituted methane derivatives 7a-d, followed by oxidative hydrogen abstraction with DDQ, and subsequent exchange of the counter-anion by using aq. HPF₆ or aq. HBF₄. In addition, the reaction of 7a-d with 2.2 equiv. amounts of DDQ afforded carbonyl compounds 12a-d. The delocalization of the positive charge of 9a-c was evaluated by the ¹H and ¹³C NMR spectral data. The thermodynamic stability of cations 9a-c was evaluated to be in the order 9a<9b<9c on the basis of their reduction potentials measured by cyclic voltammetry (CV) and pK_R+ values (2.6-10.3) obtained spectrophotometrically. The reduction waves of cations 9a-c were irreversible, suggesting the dimerization of the radical species generated by one-electron reduction. This was demonstrated by the reduction of 9a·BF₄⁻ with Zn powder to give dimerized product 14a. In addition, the quenching of 9a·BF₄⁻ with MeOH/NaHCO₃ gives ether derivative 15a, which is proposed for the precursor for synthesizing tris(heteroazulene)-substituted methyl cations bearing two different heteroazulene-units.     

KINETICS OF POLYMERIZATION OF ACRYLONITRILE INITIATED BY VANADIUM(V)-THIOUREA REDOX SYSTEM

The kinetics of polymerization of acrylonitrile (AN) initiated by quinquevalent vanadium (V~(5+))-thiourea (TU) redox system has been investigated in aqueous nitric acid in the temperature range from 30 to 50℃. The polymerization rate (R_p) can be expressed as follows: In the copolymerization of acryionitrile with methyl acrylate (MA), the reactivity ratios were found to be 1.0 and 1.1, respectively. The experimental observations suggest that the initiating species is probably a complex consisting of a central ion of Lewis acid-VO_2~+ and the ligands of Lewis bases-acrylonitrile, thiourea, and nitrate anions, while the initiating system in lower concentration, the polymerization of acrylonitrile does not occur if the thiourea is acidified prior to its reaction with quinquevalent vanadium. This indicates that the primary radicals (or the monomeric radicals in the present article) are produced by associated thiourea rather than isothlourea.