Kinetics,mechanism and cloud point measurements in the oxidative degradation of non-ionic Triton X-100 surfactant in acidic permanganate solutions

The polyoxyethylene chain of non-ionic surfactant Triton X-100 [4-(1,1,3,3-tetramethylbutyl) phenyl polyethylene glycol,TX-100] was degraded by permanganate in the presence of HClO₄. The oxidative degradation rate and cloud point have been obtained as a function of [surfactant], [permanganate], [HClO₄], and temperature. Dependence of the reaction rate on adding inorganic salts (Na₄P₂O₇, NaF and MnCl₂) was also examined. The oxidation rate increased with increase in [TX-100] and [H⁺]. The higher order kinetics with respect to [TX-100] at lower [H⁺] shifted to lower order at higher [H⁺]. The cloud point of TX-100 (67°C) shifted to lower temperature (23±0.5°C) after oxidative degradation of the polyoxyethylene chain. Evidence of complex formation between TX-100 and MnO ₄ ⁻ was obtained spectrophotometrically. Presence of the primary alcoholic (–OH) group in the TX-100 skeleton is responsible for the degradation of oxyethylene chain. Both monomeric and aggregated TX-100 molecules are oxidized by permanganate. A catalytic oxidation mechanism is proposed on the basis of the experimental findings.     

Ruthenium(III) Catalyzed Oxidative Degradation of Amitriptyline-A Tricyclic Antidepressant Drug by Permanganate in Aqueous Acidic Medium

The oxidation of amitriptyline by potassium permanganate has been investigated spectrophotometrically in the presence of ruthenium(III) as catalyst in aqueous acidic medium at a constant ionic strength of 0.20 mol⋅dm⁻³. The stoichiometry was found to be 1:1 in terms of the mole ratio of amitriptyline and permanganate ions consumed. The order of the reaction with respect to manganese(VII) and ruthenium(III) concentration was unity while the order with respect to amitriptyline was less than unity over the concentration range studied. The rate increased with an increase in acid concentration. The reaction rates revealed that the Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction. The oxidation products were identified by spectral analysis. A tentative mechanism consistent with the kinetics has been proposed. The reaction constants involved in the different steps of the reaction mechanism were calculated. Kinetic experiments suggest that HMnO₄ is the reactive permanganate species and [Ru(H₂O)₆]³⁺ is the reactive Ru(III) species.     

Reaction of ethyl bromoacetate with substituted naphthoate ions

Rate constants for the reaction of ethyl bromoacetate with three series of substituted naphthoate ions have been measured in an acetone-water mixture (90% v/v). Using σ _p values rate constants at 30^o correlate well with the Hammett equation yielding ρ=−0.54, −0.19 and −0.25 for (4,1−), (6,1−) and (6,2−) series, respectively. Comparison of these ρ values with those of the reaction of phenacyl bromide reveals the failure of the reactivity-selectivity principle RSP in these reactions. Failure of RSP has been explained in terms of isoselective temperature.     

Studies on electron transfer reactions: oxidation of phenol and ring-substituted phenols by heteropoly 11-tungstophosphovanadate(V) in aqueous acidic medium

The kinetics of oxidation of phenol and a few ring-substituted phenols by heteropoly 11-tungstophosphovanadate(V), [PV^VW₁₁O₄₀]⁴⁻ (HPA) have been studied spectrophotometrically in aqueous acidic medium containing perchloric acid and also in acetate buffers of several pH values at 25 °C. EPR and optical studies show that HPA is reduced to the one-electron reduced heteropoly blue (HPB) [PV^IVW₁₁O₄₀]⁵⁻. In acetate buffers, the build up and decay of the intermediate biphenoquinone show the generation of phenoxyl radical (ArO^·) in the rate-determining step. At constant pH, the reaction shows simple second-order kinetics with first-order dependence of rate on both [ArOH] and [HPA]. At constant [ArOH], the rate of the reaction increases with increase in pH. The plot of apparent second-order rate constant, k ₂, versus 1/[H⁺] is linear with finite intercept. This shows that both the undissociated phenol (ArOH) and the phenoxide ion (ArO⁻) are the reactive species. The ArO⁻–HPA reaction is the dominant pathway in acetate buffer and it proceeds through the OH⁻ ion triggered sequential proton transfer followed by electron transfer (PT-ET) mechanism. The rate constant for ArO⁻–HPA reaction, calculated using Marcus theory, agrees fairly well with the experimental value. The reactivity of substituted phenoxide ions correlates with the Hammett σ⁺ constants, and ρ value was found to be −4.8. In acidic medium, ArOH is the reactive species. Retardation of rate for the oxidation of C₆H₅OD in D₂O indicates breaking of the O–H bond in the rate-limiting step. The results of kinetic studies show that the HPA-ArOH reaction proceeds through a concerted proton-coupled electron transfer mechanism in which water acts as proton acceptor (separated-CPET).     

Determination of total iron in fresh waters using flow injection with potassium permanganate chemiluminescence detection

A flow injection method is described for the determination of iron in fresh water based on potassium permanganate chemiluminescence detection via oxidation of formaldehyde in aqueous hydrochloric acid. Total iron concentrations are determined after reducing Fe(III) to Fe(II) using hydroxylamine hydrochloride. The detection limit (three standard deviations of blank) is 1.0 nM, with a sample throughput of 120 h⁻¹. The calibration graph was linear over the range (2–10) × 10⁻⁷ M (r ² = 0.9985) with relative standard deviations (n = 5) in the range 1.0–2.3%. The effect of interfering cations (Ca(II), Mg(II), Zn(II), Ni(II), Co(II), Fe(III), Mn(II), Pb(II), and Cu(II)) and common anions (Cl⁻, SO ₄ ²⁻ , PO ₄ ³⁻ , NO ₃ ⁻ , NO ₂ ⁻ , I⁻, F⁻, and SO ₃ ²⁻ ) was studied at their maximum admissible concentrations in fresh water. The method was applied to fresh-water samples from the Quetta Valley, and the results obtained (0.04 ± 0.001–0.11 ± 0.01 mg/L Fe(II)) were in reasonable agreement with those obtained using the spectrophotometric reference method (0.05 ± 0.01–0.12 ± 0.02 mg/L Fe(II)). The text was submitted by the authors in English.     

Behavior of ethylene and ethane within single-walled carbon nanotubes, 2: dynamical properties

The dynamical behavior of ethylene and ethane confined inside single-walled carbon nanotubes has been studied using Molecular Dynamics and a fully atomistic force field. Simulations were conducted at 300 K in a broad range of molecular densities, 0.026 mol⋅L⁻¹<ρ<15.751 mol⋅L⁻¹(C₂H₄) and 0.011 mol⋅L⁻¹<ρ<14.055 mol⋅L⁻¹(C₂H₆), and were oriented towards the determination of bulk and confined phase self-diffusion coefficients. In the infinite time limit, Fickian self-diffusion is the dominant mode of transport for the bulk fluids. Upon confinement, there is a density threshold (ρ=5.5 mol⋅L⁻¹) below which we observe a mixed mode of transport, with contributions from Fickian and ballistic diffusion. Nanotube topology seems to have only a small influence on the confined fluids’ dynamical properties; instead density (loading capacity) assumes the dominant role. In all cases studied and at a given density, the diffusivities of ethylene are larger than those of ethane, although the difference is relatively minor. We note the collapse of self-diffusivities obtained from the bulk fluids and confined phases into a unique single trend. These results suggest that it might be possible to infer dynamical properties of confined fluids from the knowledge of their bulk phase densities. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Kinetics and mechanism of Ru(III)-catalyzed oxidation of aliphatic alcohols by trichloroisocyanuric acid in HClO4 medium

The kinetics and mechanism of Ru(III)-catalyzed oxidation of some aliphatic alcohols by trichloroisocyanuric acid (TCICA) has been studied in aqueous HOAc-HClO₄ medium. The reaction is zero order in [TCICA], fractional order in [alcohol] and first order in [Ru(III)]. The reaction is insensitive towards changes in acid concentration. The rate is not affected by an increase in [Cl⁻]. The polar reaction constant (ρ*) was found to be −1.27 at 308 K. A mechanism involving complex formation between the substrate and catalyst in the fast equilibrium step followed by its decomposition in a slow step is proposed.     

Iron(III)–salen–H<Subscript>2</Subscript>O<Subscript>2</Subscript> as a peroxidase model: electron transfer reactions with anilines

Abstract  

Iron(III)–salen complexes catalyze the H₂O₂ oxidation of various ring-substituted anilines in MeCN have been studied, and [O=Fe^IV(salen)]^+· is proposed as the active species. Study of the kinetics of the reaction by spectrophotometry shows the emergence of a new peak at 445 nm in the spectrum which corresponds to azobenzene. Further oxidation of azobenzene by H₂O₂ leads to the formation of azoxybenzene. ESI–MS studies also support the formation of these products. The rate constants for the oxidation of meta- and para-substituted anilines were determined from the rate of decay of oxidant as well as the rate of formation of azobenzene, and the reaction follows Michaelis–Menten kinetics. The rate data show a linear relationship with the Hammett σ constants and yield a ρ value of −1.1 to −2.4 for substituent variation in the anilines. A reaction mechanism involving electron transfer from aniline to [O=Fe(salen)]^+· is proposed. The presence of axial ligands modulates the activity of the complex.     

Catecholase biomimetic catalytic activity of copper(II) complexes with 2-methyl-3-amino-(3H)-quinazolin-4-one

The oxidation of catechol by molecular oxygen in the presence of a catalytic amount of copper(II) complex with 2-methyl-3-amino-(3H)quinazoline-4-one (MAQ) and various anions (Cl⁻, Br⁻, ClO ₄ ⁻ , SCN⁻, NO ₃ ⁻ and SO ₄ ^– ) was studied. The catecholase biomimetic catalytic activity of the copper(II) complexes has been determined spectrophotometrically by monitoring the oxidative transformation of catechol to the corresponding light absorbing o-quinone (Q). The rate of the catalytic oxidation reaction was investigated and correlated with the catalyst structure, time, concentration of catalyst and substrate and finally solvent effects. Addition of pyridine or Et₃N showed a dramatic effect on the rate of oxidation reaction. Kinetic investigations demonstrate that the rate of oxidation reaction has a first order dependence with respect to the catalyst and catechol concentration and obeying Michaelis–Menten Kinetics. It was shown that the catalytic activity depends on the coordination environment of the catalyst created by the nature of counter anions bound to copper(II) ion in the complex molecule and follows the order: Cl⁻ > NO ₃ ⁻ > Br⁻ > SO ₄ ^– > SCN⁻ > ClO ₄ ⁻ . To further elucidate the catalytic activity of the complexes, their electrochemical properties were investigated and the catecholase mimetic activity has been correlated with the redox potential of the Cu²⁺/Cu⁺ couple in the complexes.     

Indirect photometric determination of europium(II) in some inorganic materials containing aliovalent europium species

A procedure is proposed for the indirect spectrophotometric determination of trace europium(II) in poorly soluble inorganic materials. The approach based on sample dissolution in the presence of excess vanadium(V) salts followed by the determination of vanadium(IV), equivalent to the concentration of europium(II), is used. The photometric determination of V(IV) is based on its oxidation with a potassium permanganate solution followed by the measurement of absorbance of excess MnO₄⁻. The procedure is applied to the analysis of EuF_{3 − x} with low europium(II) concentrations in the study the dissolution products of europium fluorides in salt melts and in the study the products of sorption europium(II) by strontium fluorapatite from salt melts. The proposed procedure is rapid and simple. It possesses satisfactory performance characteristics.