Kinetic Studies on the Reaction of Sodium Hexa-cyanoferrate(II) Complex with Peroxydisulfate Anion

Introduction In the previous studies on the oxidation reaction,peroxydisulfate was widely used as an oxidizingagent.1-5 One of the advantages of this oxidant lies in itsstability in a wide range of pH values. The reaction be-tween Fe(CN)5L3- (L=N-aromatic heterocyclic li-gands) and S2O8 2- has been proved to proceed throughan outer-sphere electron transfer mechanism.5 For a re-action [(Eq. (1)] to be under an outer-sphere mechanismthe steps involved are the formation of a reactant …     

Micellar and Mixed-Micellar Effects on Alkaline Hydrolysis of tris(1,10–phenanthroline)iron(II): Kinetic Exploration

The kinetics of alkaline hydrolysis of tris(1,10–phenanthroline)iron(II) has been studied in the presence of nonionic and mixed nonionic–ionic micellar media at 308 K. The effects of mixed-micellar environments of nonionic with ionic surfactants (C₁₂E₂₃/ATABs and C₁₂E₂₃/SDS) on the hydrolytic rate have been studied. The rate decreases monotonically with an increment of [C₁₂E₂₃]_T (total Brij 35 concentration) at constant [^?OH]₀ and has been discussed with the pseudo-phase micellar model. The rate also decreases with [C₁₂E₂₃]_T at a continuous addition of ionic surfactants (ATABs and SDS). The observed rate constant k_obs follows the empirical relation: k_obs = (k₀ + θK [C₁₂E₂₃]_T)/(1 + K [C₁₂E₂₃]_T) (where θ and K are empirical constants). The values of θ remain unaffected, whereas K decreases nonlinearly with [ATABs]_T in a mixed C₁₂E₂₃?ATAB micellar system. But the k_obs in a mixed C₁₂E₂₃–SDS micellar system is much lower than that of the C₁₂E₂₃–ATAB system and do not comply with any micellar kinetic models.     

Investigations on the redox behaviour of manganese in manganese(II)–saccharin and manganese(II)–saccharin–1,10-phenanthroline complexes

The redox behaviour of manganese system in Mn–Sac and Mn–Sac–Phen complexes were studied using cyclic voltammetry technique at glassy carbon electrode (GCE) in 0.1 M KCl electrolyte. The CV of Mn–Sac solution is more or less similar to that of uncoordinated Mn (in MnCl₂) accept slight difference in peak position and peak current. The presence of secondary ligand phenanthroline (in Mn–Sac–Phen complex) changes the CV of Mn system largely compared to those of uncoordinated Mn and Mn–Sac. The redox system is irreversible in Mn–Sac and quasi-reversible in Mn–Sac–Phen complex. The effect of concentration and pH on the redox behaviour of Mn system have been studied for both the complexes.     

Effect of ethylene glycol on micellization and micellar-catalyzed alkaline hydrolysis reaction of a cationic surfactant at 293–313 K

Changes in critical micellar concentrations (CMC’s) of gemini surfactant, α, ω-ethane bis(dimethyl cetyl ammonium bromide) (C₁₆-2-C₁₆) with different concentrations of ethylene glycol (EG) addition have been investigated by electrical conductivity method. Subsequently, alkaline hydrolysis of ethyl acetate (EA) in the presence of C₁₆-2-C₁₆ and C₁₆-2-C₁₆-EG has been studied conductometrically at 303.2 and 313.2 K, respectively. It was found that an increase in concentrations of EG added to C₁₆-2-C₁₆ aqueous solutions caused an increase in CMC’s of C₁₆-2-C₁₆, provoked by the decrease in the interfacial Gibbs energy contribution to G _M^∘. The hydrolysis of EA showed catalytic and restrained dual behavior in the presence of surfactant, it may be related to higher microviscosity and change of morphology with increased surfactant for C₁₆-2-C₁₆ at higher concentration. Addition of EG did not change microenvironment in micellar interfacial region significantly, which had less effect on gemini C₁₆-2-C₁₆ micellar catalytic efficiency.     

The effect of Fe(II) ions on the 1,10-phenanthroline and neocuproine intercalates of γ-zirconium phosphate

1,10-Phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neocuproine), and 4,7-dimethyl-1,10-phenanthroline have been intercalated between layers of -zirconium phosphate (-ZrP). The observed interlayer distances are not a simple function of the size of guest molecules. Despite the fact that -ZrP takes up very few Fe²⁺ ions, the phen and neocuproine intercalates do take up some Fe²⁺ ions without further changes in the interlayer distances. The chemical environments around Fe²⁺ ions between layers of the intercalates were investigated by⁵⁷Fe Mössbauer spectroscopy. A fairly large fraction of the Fe²⁺ ions was found to be in a high-spin state. The low-spin [Fe(phen)₃]²⁺ ions are also ion exchanged on -ZrP, with the expansion of the interlayer up to 19.9 Å.     

Role of anions in the kinetics of the acid catalyzed dissociation of tris-(2,2′bipyridine) Fe(II) complex

Excess of Cl⁻ and NO₃⁻ ions bring about a significant increase in the rate of dissociation of the tris-(2,2′bipyridine) Fe(II) complex in HCl, HClO₄ and H₂SO₄ in a very narrow range of H⁺ concentration (∼0·1−0·3 M). Above and below this concentration range, these anions do not lead to significant variation in the rate of dissociation. This points to the involvement of these ions in a kinetic step which is only important in the rate expression in this narrow range. It is suggested that the anions occupy the coordination site left vacant by the partial dissociation of the complex leading to the half bonded intermediate. This would significantly lower the free energy of activation for the subsequent protonation step leading to complete dissociation and thus lead to acceleration. The lowering of the free energy of activation will be mainly due to an increase in entropy of this intermediate on account of charge reduction and lower rigidity due to lack of hydrogen bonding. The retarding effect of SO₄²⁻ concentrations and the unambiguously interpreted as its addition leads to simultaneous changes in H⁺ and HSO₄⁻ concentrations and the possibility of ion pair formation with the complex cannot be ruled out.     

Kinetic studies on the reactions of Ru(II) tetraammines with CS2N−3

The kinetics of the reactions of Ru(II) complexes with CS₂N⁻₃ ions were studied spectrophotometrically. The formation rate constants data for trans-[Ru(NH₃)₄L(CS₂N₃)] are 2.2 × 10², 1.8 × 10 and 1.3 × 10² M⁻¹ s⁻¹ for L = SO^2-₃, HSO⁻₃ and P(OEt)₃), respectively [μ = 1.0 M (NaCF₃COO), 25°C]. Under the same experimental conditions, the values of k⁻¹ (specific rate for the aquation reaction) are 1.5 × 10⁻², 5.0 × 10⁻² and 4.5 × 10 s⁻¹ for L = SO²⁻₃, HSO⁻₃ and P(OEt)₃, respectively. The free-energy change (ΔG^≠) for the systems where L = P(OEt)₃ and SO²⁻₃ are in agreement within the experimental error. It was observed that the affinity of the CS₂N⁻₃ ion decreases with the increasing π-acidity of the auxiliary ligand L. The order of affinity of the CS₂N⁻₃ ion for the Ru(II) center studies is SO²⁻₃ > HSO⁻₃ > P(OEt)₃ >SO₂.     

Kinetic Determination of Nanogram Levels of Manganese(II) by Naphthol Blue Black–Potassium Periodate–1,10-Phenanthroline System

 The catalytic effect of manganese(II) on the oxidation of Naphthol Blue Black, with potassium periodate in the presence of 1,10-phenanthroline in weakly acidic media is studied. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance of the dye at 618 nm. Under the optimum conditions (3 × 10⁻⁵ mol dm⁻³ Naphthol Blue Black, 6 × 10⁻⁴ mol dm⁻³ potassium periodate, 1 × 10⁻⁴ mol dm⁻³ 1,10-phenanthroline, 0.1 mol dm⁻³ acetate buffer – pH 4.0, 60 °C, 5 min) manganese(II) in the range 0.08–4 ng cm⁻³ can be determined by the fixed-time method with a detection limit of 0.025 ng cm⁻³. The influence of foreign ions on the accuracy of the results is investigated. The developed method is highly sensitive, selective, and simple. The method was applied successfully to the determination of manganese in cucumbers, garlic cloves and parsley leaves. Received June 12, 2000. Revision December 12, 2000.     

Effect of some added salts on the kinetics of dissociation of tris-2,2′-bipyridine-Fe(II) complex

Both monovalent cations and anions show a regular gradation, according to their sizes, in their effect on the rate and the activation parameters for the dissociation of tris(2,2′-bipyridine)-Fe(II) complex in acid. ΔS and ΔH of activation in M, 0.1 M and 0.01 M acid decrease in the order Cl⁻ > Br⁻ > I⁻ for anions and Li⁺ > Na⁺ > Cs⁺ for cations. The effect of the bulky tetra-alkyl ammonium ions is anomalous and does not depend on their sizes. The effect of the anions can be rationalized in terms of their involvement with the vacant coordination site of the partially bonded intermediate. The effect of cations is probably due to their altering the water structure at high concentration. The anomalous of the tetra-alkyl ammonium ions supports this view.     

Kinetic and mechanistic investigations on the oxidation of N’-heteroaryl unsymmetrical formamidines by permanganate in aqueous alkaline medium

Kinetic studies on the oxidation of two substituted azinyl formamidines (Azn-Fs), namely N,N-dimethyl-N’-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F), by alkaline permanganate have been performed by spectrophotometry. The spectroscopic and kinetic evidence reveals the formation of 1:1 intermediate complexes between the oxidant and substrates. The influence of pH on the oxidation rates indicated that the reactions are base-catalyzed. The reactions show identical kinetics, being first order each in [MnO₄ ^?]₀ and [Azn-F]₀, but with a fractional first-order dependence on [OH^?]. The effect of temperature on the reaction rate has been studied. Increasing ionic strength has no significant effect on the rate. The final oxidation products of Pym-F and Py-F were identified as 2-aminopyrimidine and 2-aminopyridine, respectively, in addition to dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate of Py-F is higher than that of Pym-F. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-limiting step of the reactions, along with thermodynamic quantities, are presented and discussed.     

Studies on outer-sphere electron transfer reactions of surfactant–cobalt(III) complexes with iron(II) in liposome (dipalmitoylphosphotidylcholine) vesicles

The effect of unilamellar vesicles of dipalmitoylphosphotidylcholine (DPPC), both below and above the phase transfer region, on the second-order rate constants for outer-sphere electron transfer between Fe²⁺ and the surfactant?Ccobalt(III) complexes, cis-[Co(en)₂(C₁₂H₂₅NH₂)₂]³⁺ and cis-[Co(trien)(C₁₂H₂₅NH₂)₂]³⁺ (en?=?ethylenediamine, trien?=?triethylenetetramine, C₁₂H₂₅NH₂?=?dodecylamine) was studied by UV?CVis absorption spectroscopy. Below the phase transition temperature of DPPC, the rate decreased with increasing concentration of DPPC, while above the phase transition temperature the rate increased with increasing concentration of DPPC. It is concluded that below the phase transition temperature, there is an accumulation of surfactant?Ccobalt(III) complexes at the interior of the vesicle membrane through hydrophobic effects, and above the phase transition temperature the surfactant?Ccobalt(III) complex is released from the interior to the exterior surface of the vesicle. Through isokinetic plots, we have established that the mechanism of the reaction does not alter during the phase transition of DPPC.     

Effect of alkaline and alkaline–earth cations on the supercapacitor performance of MnO2 with various crystallographic structures

The electrochemical performances of the α-, γ-, and δ-MnO₂ with different crystallographic structures were systematically investigated in 0.5 mol/L Li₂SO₄, 0.5 mol/L Na₂SO₄, 1 mol/L Ca(NO₃)₂, and 1 mol/L?Mg(NO₃)₂ electrolytes. The results showed that the electrochemical performances of the manganese dioxides depended strongly on the crystallographic structures of MnO₂ as well as the cation in the electrolytes. Because the δ-MnO₂ consists with layers of structure and the interlayer separation is 7 Å, which is suitable for insertion/extraction of some alkaline and alkaline–earth cations, the δ-MnO₂ electrode showed the higher specific capacitance than that of α-MnO₂ and γ-MnO₂. We also found that the α-, γ-, and δ-MnO₂ electrodes in the Mg(NO₃)₂ electrolyte showed a higher specific capacitance, while all the α-, γ-, and δ-MnO₂ electrodes in the Li₂SO₄ electrolyte exhibited a better cycle life. The reason for the different behavior of Li⁺ and Mg²⁺ during the charge/discharge process can be ascribed to the charge effect of the cations in the electrolytes. The ex situ X-ray diffraction (XRD) and long-time cyclic voltammogram measurements were used to systematically study the energy storage mechanism of MnO₂-based electrodes. A progressive crystallinity loss of the materials is also observed upon potential cycling at the oxidized states. A reasonable charge/discharge mechanism is proposed in this work.     

Equilibria in complexes of n-heterocycles—XLVI. Polymorphism and solvatochromism in some salts of the tris-(1,10-phenanthroline) nickel(II) ion

The extensive polymorphism among hydrated racemic and resolved salts of tris-1,10-phenanthrolinenickel(II), notably the iodides, [Ni(phen)₃]I₂·nH₂O, is described.     

Synthesis and magnetic characterization of Ln(III)–Co(II) complexes with 1,10-phenanthroline ligands

Four heteronuclear complexes, [Ln₂Co₂L₁₀(H₂O)(phen)₂] · n(H₂O) (Ln = La 1, n = 2; Ln = Nd 2, Sm 3, Gd 4, n = 0; HL = α-methylacrylic acid, phen = 1,10-phenanthroline), have been synthesized and characterized by elemental analysis, IR and X-ray diffraction. The complexes with a discrete Co–Ln–Ln–Co tetranuclear molecule are isomorphous in the triclinic space group P 1 and Z = 1, in which all metal ions are bridged by bidentate α-methylacrylato groups. Magnetic measurements of 1, 2 and 3 show antiferromagnetic exchange interaction between paramagnetic centers.     

Kinetic catalytic determination of trace Cu(II) in water samples with the thioglycolic/thiolactic acid–chromate reaction

The use of two novel similar indicator reactions as applied to the kinetic determination of Cu(II) in water is investigated. The methods rely on the catalytic effect of the analyte on the oxidation of thioglycolic (TGA) and thiolactic (TLA) acids by chromate in acidic media. The extent of the reactions was followed spectrophotometrically at 345 nm. Pseudo-first-order rate coefficients, k_obsd, were determined as a function of catalyst concentration. Interference of Fe(III) and Pb(II) was suppressed by complexation with pyrophosphate. For the reaction of TGA, a linear regression for k_obsd versus [Cu(II)] was obtained for the entire concentration range considered. Although the plot corresponding to TLA oxidation exhibits a sharp change of slope at approximately 1.8×10^–5 M Cu(II), it can still be described effectively by two linear regressions with different slopes. The reaction of TGA is more sensitive than that of TLA at low Cu(II) concentration. The opposite is true for higher catalyst contents. The detection limits were 65 gL^–1 for TGA and of 80 gL^–1 for TLA oxidation, respectively. The relative standard deviations, of 0.4% for TGA and 1.1% for TLA oxidation, respectively, were obtained for five replicate runs at 1000 g L^–1. Samples of river and wastewater from the mining region of Baia-Mare, Northern Romania were analyzed using the more sensitive reaction of thioglycolic acid. Results were compared to those obtained by the officially standardized methods. Good agreement was obtained, even for an untreated sample. Measurements did not require prior separation of interfering species.     

Effect of substitution degree of 2-hydroxypropyl-β-cyclodextrin on the alkaline hydrolysis of cinnamaldehyde to benzaldehyde

The yield of benzaldehyde in the 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD), with a low degree of substitution (DS = 3.9), catalytic system was 70%, which was higher than that of the system with 8.8 DS under the optimised conditions (323 K, 2% NaOH (w/v), cinnamaldehyde:2-HP-β-CD = 1:1 (molar ratio)). Due to the structural complementary effects of the host and guest, cyclodextrins (CDs) played the catalysis role in the reaction, which was confirmed by kinetic studies and solubilisation. The characterisation of NMR and fluorescence measurement suggested that the extent of hydroxypropyl substitution affected the cavity structure of the CD molecule. The hydroxypropyl groups at O₂ positions were spatially spread out but restricted, which affected the molecular encapsulation capabilities.     

Tuning the hemilabile behaviour of a thioether–pyrazole ligand on Pd(II) complexes with diphosphines

The coordination mode of thioether–pyrazole ligand, 1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane (bdtp) and 1,8-bis-(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo) ligands, in Pd(II) complexes containing a diphosphine ligand is determined by subtle changes in size of the bridge between the two phosphorus atoms. The ¹H NMR and ³¹P{¹H} NMR at variable temperature in acetonitrile solution prove that the hemilabile character of the bdtp ligand depend on the diphosphine ligand. Thus, while in [Pd(bdtp)(dppe)](BF₄)₂ [1](BF₄)₂ the thioether group not participate in the Pd(II) coordination sphere, two isomers with different coordination (P₂N₂ vs P₂NS) are in equilibrium in [Pd(bdtp)(dppp)](BF₄)₂ [2](BF₄)₂ acetonitrile solution. For complexes [Pd(bddo)(dppe)](BF₄)₂ [3](BF₄)₂ and [Pd(bddo)(dppp)](BF₄)₂ [4](BF₄)₂, only the coordination N,N is observed.     

Tuning the hemilabile behaviour of a thioether–pyrazole ligand on Pd(II) complexes with diphosphines

The coordination mode of thioether–pyrazole ligand, 1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane (bdtp) and 1,8-bis-(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo) ligands, in Pd(II) complexes containing a diphosphine ligand is determined by subtle changes in size of the bridge between the two phosphorus atoms. The ¹H NMR and ³¹P{¹H} NMR at variable temperature in acetonitrile solution prove that the hemilabile character of the bdtp ligand depend on the diphosphine ligand. Thus, while in [Pd(bdtp)(dppe)](BF₄)₂ [1](BF₄)₂ the thioether group not participate in the Pd(II) coordination sphere, two isomers with different coordination (P₂N₂ vs P₂NS) are in equilibrium in [Pd(bdtp)(dppp)](BF₄)₂ [2](BF₄)₂ acetonitrile solution. For complexes [Pd(bddo)(dppe)](BF₄)₂ [3](BF₄)₂ and [Pd(bddo)(dppp)](BF₄)₂ [4](BF₄)₂, only the coordination N,N is observed.