Exploration of Ruthenium (III) Chloride catalysis on oxidative conversion of aryloximes to arylaldehydes with bromamine-B: A kinetic and mechanistic approach

Conversion of aryloximes to corresponding arylaldehydes is an important oxidative transformation in synthetic chemistry. In the course of this research, optimum conditions for the facile oxidation of benzaldehyde oxime and p-substituted benzaldehyde oximes viz., p-hydroxybenzaldehyde oxime, p-methoxy benzaldehyde oxime, p-bromobenzaldehyde oxime and p-nitrobenzaldehyde oxime (aryloximes) with bromamine–B (BAB) catalyzed by ruthenium (III) chloride (RuCl3) in perchloric acid (HClO4) medium have been kinetically investigated at 303 K. All the five aryloximes follow identical kinetics with a first-order dependence of rate on [BAB]o, fractional-order each on [aryloximes]o and [RuCl3], and an inverse fractional-order on [H+]. Activation parameters have been evaluated. Oxidation products were characterized by spectral analysis. Under the identical set of experimental conditions, the kinetics of catalyzed reactions has been compared with uncatalyzed reactions and found that the catalyzed reactions are 4–6 folds faster. Isokinetic temperature is found to be 338 K. The catalytic constants (Kc) have been calculated at different temperatures and the values of activation parameters with respect to the catalyst have been evaluated. Spectroscopic evidence for the formation of 1:1 complex between BAB and RuCl3 has been obtained. The observed results have been explained by a plausible mechanism and the related rate law has been deduced. The present method offers many advantages including high conversion, short reaction times and the involvement of non-toxic reagents.

Kinetic compensation effect of isoconversional methods

For experimental data obtained under different reaction/process conditions over time or temperature, the kinetic compensation effect (KCE) can be expected. Under dynamic (nonisothermal) conditions, at least two analytical pathways forming the KCE were found. Constant heating rate (q = const) and variable conversion degrees (α = var) lead to a vertical source of the KCE, called the isochronal effect. In turn, for a variable heating rate (q = var) and constant conversion degree (α = const), we can obtain an isoconversional compensation effect. In isothermal conditions (analyzed as polyisothermal), the KCE appears only as an isoconversional source of the compensating effect. The scattering of values for the determined isokinetic temperatures is evidence of a strong influence of the experimental conditions and the calculation methodology. The parameters of the Arrhenius law have been shown to allow the determination of the KCE and further the isokinetic temperature. In turn, using the Eyring equations for the same parameters, we can determine the enthalpy–entropy compensation (EEC) for the activation process and the compensation temperature, which is often treated as an isokinetic temperature. KCE effects have also been shown to be able to be amplified or dissipated, but isokinetic temperature is not a compensating quantity in the literal sense in isoconversional methods because $${T}_{iso}\to \infty .$$ T iso → ∞ . Thus, in isoconversional methods, isoconversional KCE values are characterized by strong variability of activation energy corresponding to the weak variation of the pre-exponential factor, which in practice means that $${\text{ln}}\mathit {A}\to {\text{const}}.$$ ln A → const . This is completely in line with the classical Arrhenius law.

Thermodynamic Parameters of the Viscous Flow in the Aqueous Solutions of Polyols

Data experimentally obtained for the kinematic viscosity are used to calculate the thermodynamic characteristics of viscous flows in some polyols and their aqueous solutions. The solutions of glycerol, erythritol, xylitol, adonite, sorbitol, mannitol, and dulcite are studied, as well as the melts of erythritol, xylitol, and sorbitol. The entropy, enthalpy, and free energy of the viscous flow are calculated in the framework of the theory of reaction rate constants. A linear dependence between the true entropy and the enthalpy of the viscous flow in the researched systems is found, which allowed us to determine the isokinetic temperature, calculate the transmission coefficient, draw a conclusion about the mechanisms of bond formation in the reaction centers of active complexes, and estimate the vibration energy of those bonds.

Correlation for Photocatalytic Degradation Kinetics of Carboxylic Acids using Electrochemically Synthesized Al2S3 Nanoparticles and Study of Antibacterial Activity

Aluminium sulfide (Al2S3) nanoparticles were successfully synthesized by electrochemical method. Further, the synthesized nanoparticles were used as a photocatalyst for degradation of trichloroacetic acid, chloroacetic acid, acetic acid and degradation kinetics was studied by volumetric method using NaOH under various experimental conditions. The Al2S3 nanoparticles were characterized by UV-visible spectroscopy, X-ray diffraction and SEM-EDAX. The study of UV-visible spectroscopy indicates that Al2S3 nanoparticles shows maximum intensity peak at 222 nm in the UV region and there is no absorption peak in the visible region, therefore the synthesized nanoparticles is active under UV light and band gap energy was found to be 3.07 eV, which was calculated using Tauc plot. The structure of Al2S3 was found to be tetragonal structure and average crystal size was found to be 25.76 nm, which was calculated using Debye-Scherrer′s formula. The SEM results showed that Al2S3 appears as nanoflakes with agglomerated. The presence of aluminium and sulfur was confirmed using EDAX spectra. The photocatalytic activity of the synthesized Al2S3 nanoparticles was examined by taking three carboxylic acids by volumetric method. Taft LFER was tested, the isokinetic temperature β was calculated for oxidation of carboxylic acids. The antibacterial activity was investigated for synthesized nanoparticles by using Bacillus subtilis MTCC 2763 and Escherichia coli MTCC 40 of different bacteria.

Meyer-Neldel rule in the conductivity of phase separated manganites

Meyer-Neldel behaviour of the conductivity of phase separated La1−xCaxMnO3 manganite system in the low Ca-doping range has been investigated. Evolution of the isokinetic temperature of the conductivity, modified by Ca-doping, hydrostatic pressure and current bias has been determined. In addition, the evolution of the isokinetic temperature with ageing has also been studied. It is found that the Meyer-Neldel behaviour of the manganite system stems from multi-excitation entropy mechanism. The isokinetic temperatures estimated from pressure and doping effects coincide but differ from those determined using current and ageing controlled conductivity changes. It is concluded that in the presence of a detailed theoretical model of the excitations coupling in manganites, the investigations of the Meyer-Neldel effect may became a powerful tool for characterization and investigation of transport mechanisms in phase separated manganites.

Hole and Protonic Polarons in Perovskites

Electric charge transport is an essential process for all electrical and electrochemical energy systems, including inanimate and animate matter. In this issue on materials for energy conversion, we compare and discuss the role of electron holes and protons as charge carriers in solids. Specifically we outline how the temperature or thermal bath affect the charge carrier concentration and mobility for some metal oxides with the perovskite structure. The frequent observation that the conductivity becomes independent of the activation energy at the isokinetic temperature, known as the Meyer-Neldel rule, is an important aspect of our interpretation of the physical mechanism of conduction by polaron hopping.

Spectral and Thermal Studies of Some Nucleic Acid Complexes

Barbituric acid, thiobarbituric acid and thiouracil complexes with sodium and potassium chlorides were prepared and characterized by UV in different solvents and IR experimentally and theoretically using B3LYP method and Gaussian program. The composition of the studied complexes was also confirmed by elemental and thermal analysis, TG, DTA and DSC techniques to determine thermodynamic parameters (Ea, ΔH, ΔS and ΔG). The negative value of entropy of activation indicated the fragments have ordered structures than undecomposed complexes. The positive values of enthalpy of activation of the decomposition stages indicated that the process is endothermic. The positive values of free energy of the decomposition indicated non-spontaneous process. Evaluation of kinetics parameters were done. The isokinetic temperature β is 407 K, which is lower than experimental temperature range, confirming the processes is entropy control. However, the plots of ΔH versus ΔS for the complexes under investigation gave straight line indicating a close similarity in the mechanism.