Kinetics of the thermal decomposition of 2,2′-azobis(2-methylpropionamidine)dihydrochloride studied by the potentiometric method using metal complexes

A potentiometric method was proposed for the determination of rate constants for peroxyl radical generation using the reduced form of the metal in the complex. The kinetics of the thermal decomposition of 2,2′-azobis(2-methylpropionamidine)dihydrochloride was studied. The requirements for an electron donor (reactant) were formulated. The iron(ii) complex with EDTA, the iron(ii) complex with o-phenanthroline, and potassium hexacyanoferrate(ii) were used as reactants. The rate for peroxyl radical generation and the generation rate constant (the latter turned out to be (0.92±0.06)?10^–6 s^–1) were calculated. The studies were carried out for different temperatures and concentrations of the initiator and complex.     

Approximate series solution of fourth-order boundary value problems using decomposition method with Green’s function

This paper proposes a new efficient approach for obtaining approximate series solutions to fourth-order two-point boundary value problems. The proposed approach depends on constructing Green’s function and Adomian decomposition method (ADM). Unlike existing methods like ADM or modified ADM, the proposed approach avoids solving a sequence of nonlinear equations for the undetermined coefficients. In fact, the proposed method gives a direct recursive scheme for obtaining approximations of the solution with easily computable components. We also discuss the convergence and error analysis of the proposed scheme. Moreover, several numerical examples are included to demonstrate the accuracy, applicability, and generality of the proposed approach. The numerical results reveal that the proposed method is very effective and simple.     

Kinetics of thermal decomposition of γ-irradiated and unirradiated complexes of mandelhydroxamic acid

The thermal decomposition of -irradiated and unirradiated complexes of mandel-hydroxamic acid (HMA), Co(HMA)₂.1/2H₂O, Mn(HMA)₂.2H₂O, Ba(HMA)₂.2H₂O and Cd(HMA)₂.2H₂O have been studied thermogravimetrically (under isothermal conditions). The thermal dehydration of each complex occurred in one step, while the decomposition of dehydrated complexes occurred in two steps. The kinetic parameters for dehydration were computed by different models. The thermal dehydration is regulated by random nucleation A₃ for Co-, Mn-, and Cd-complexes and by phase-boundary (R₃) for Ba-complex. The effect of -irradiation on the kinetic parameters of thermal decomposition is discussed. Radiation did not modify the mechanism of the reaction but accelarated the dehydration steps in the case of Mn- and Co-complexes.     

Kinetics of thermal decomposition of a synthetic K–H3O jarosite analog

The thermal decomposition kinetics of a synthetic K–H₃O jarosite analog was determined from thermogravimetric analysis at various heating rates in air. A thermal decomposition mechanism was proposed based on X-ray analysis of partially decomposed material and distinct features observed during thermal decomposition analysis. The decomposition path is complex. The material was treated as a composite of K-jarosite, H₃O-jarosite, and a “vacancy component”. The evolution of (OH)^? and SO₃ from these individual components was modeled. The decomposition is broken into subreactions according to distinct features in the thermoanalytical measurements. The subreactions are arranged sequentially and in parallel according to the evolution of the participating phases. A set of associated apparent activation energies was determined using isoconversion analysis. Kinetic triplets were assigned to each subreaction. A reasonable match with the observed decomposition was achieved by varying pre-exponential factors.     

Pattern recognition methods in the study of thermal decomposition of α-amino acids

There are many examples in the literature of a strict relation between the pathways of decomposition of a drug substance and chemical structure of its molecule. For this reason, a study has now been performed on the relation between thermal decomposition of ??-amino acids and their chemical structure. To achieve this goal, a group of a dozen or so compounds was chosen at random, and the results obtained using the DTA, TG and DTG analyses of their thermal decomposition were interpreted by highly advanced multivariate methods, principal component analysis and cluster analysis. By this statistical analysis, the influence of specific functional groups on thermal decomposition of ??-amino acids was determined. It has been found that first two principal components explain together more than 75?% of variance, and in an exceptional case, about 90?%. The third stage of decomposition was that at which the thermoanalytical data were best correlated with chemical constitution of a compound. It has also been recognized that a better discrimination among the analysed compounds was obtained for the DTA data set. The results can be useful for identification of a relation between the pathway of degradation of a drug substance and chemical structure of its molecule, and for predicting chemical stability of the compounds studied.     

Photodegradation of EDTA using Fenton’s reagent: a pilot-scale study

The presence of ethylenediaminetetraacetic acid (EDTA) in decontamination wastes can cause complexation of cations resulting in interferences in their removal by various treatment processes, for example chemical precipitation, ion exchange, etc., and can negatively affect the quality of the final form of the waste. Advanced oxidation processes using ozone, H₂O₂, ultrasonics (US), ultraviolet (UV) light, Fenton’s reagent (Fe(II) + H₂O₂), alone or in combination, are regarded as possible methods of clean and ecologically safe remedial treatment for the degradation of organics. In this study, the development of a column photoreactor (15 L) and a shallow-tank photoreactor (100 L) was carried out at the Centralised Waste Management Facility, Kalpakkam, India. Pilot-scale (batch) studies of the photocatalytic degradation of EDTA (20,000 mg/L) using UV + Fenton’s reagent in these reactor geometries were attempted. The effect of the power of the UV radiation on the kinetics of photodegradation of EDTA (20,000 mg/L) was studied using the column photoreactor. The shallow-tank reactor was used to study the photodegradation of EDTA (20,000 mg/L) using UV radiation, visible radiation, and sunlight. The successful use of sunlight as a source of energy and its greater effectiveness than UV radiation in the treatment of EDTA are presented.     

Mössbauer study of the thermal decomposition of alkali dihydroxo tetrapropionato ferrates(III)

Thermal decomposition of alkali dihydroxo tetrapropionato ferrates(III), M₃[Fe(C₂H₅COO)₄(OH)₂]xH₂O (M=Li, Na, K) has been studied upto 973 K. The complexes were calcined isothermally at various temperatures i. e., 473, 573, 773 and 973 K. The intermediates/products have been characterized by Mössbauer, infrared spectroscopies and XRD powder diffraction. The anhydrous complexes directly decompose to give -Fe₂O₃ and alkali metal carbonate without undergoing reduction to iron(II) moiety. An increase in the particle size and internal magnetic field of -Fe₂O₃ has been observed with increasing decomposition temperature. At higher temperature (973 K) MFeO₂ is formed as the final thermolysis product due to a solid state reaction between -Fe₂O₃ and alkali metal carbonate.     

Hierarchical enumeration of Kekulé’s benzenes,Ladenburg’s benzenes,Dewar’s benzenes,and benzvalenes by using combined-permutation representations

The group hierarchy for each skeleton of ligancy 6 is formulated to be: point group (PG \({\varvec{G}}_{\sigma }\)) \(\subseteq \) RS-stereoisomeric group (RS-SIG \({\varvec{G}}_{\sigma \widetilde{\sigma }\widehat{I}}\)) \(\subseteq \) stereoisomeric group (SIG \(\widetilde{{\varvec{G}}}_{\sigma \widetilde{\sigma }\widehat{I}}\)) \(\subseteq \) isoskeletomeric group (ISG \(\widetilde{\widetilde{{\varvec{G}}}}_{\sigma \widetilde{\sigma }\widehat{I}}\) = \({\varvec{S}}^{[6]}_{\sigma \widehat{I}}\)), where we start from the PG \({\varvec{G}}_{\sigma }\) = \({\varvec{D}}_{6h}\) for the Kekulé benzene skeleton, from the PG \({\varvec{G}}_{\sigma }\) = \({\varvec{D}}_{3h}\) for the Ladenburg benzene skeleton, from the PG \({\varvec{G}}_{\sigma }\) = \({\varvec{C}}_{2v}\) for the Dewar benzene skeleton, or from the PG \({\varvec{G}}_{\sigma }\) = \({\varvec{C}}_{2v}\) for the benzvalene skeleton. After these groups are constructed as combined-permutation representations, the calculation of the respective cycle indices with chirality fittingness (CI-CFs) and the introduction of ligand-inventory functions are conducted to give generation functions for 3D-based enumerations (for PGs and RS-SIGs) and 2D-based enumerations (for SIGs and ISGs). The enumeration results are discussed by means of isomer-classification diagrams, in which equivalence classes under enantiomerism (for PGs), RS-stereoisomerism (for RS-SIGs), stereoisomerism (for SIGs), and isoskeletomerism (for ISGs) are illustrated schematically. The implicit connotations of the conventional terms “skeletal isomerism”, “positional isomerism”, and “constitutional isomerism” are discussed, where the effects of the concept of isoskeletomerism are emphasized.     

The first solvation shell of Reichardt’s dye in ionic liquids: a semiempirical study

The nature of solvation of Reichardt’s dye in ionic liquids is investigated through semiempirical calculations. We build on the basis of electrostatic considerations a cluster of three ionic pairs that represent the first solvation shell of the dye. The spatial organization of this shell is a balance between sterical, electrostatic and, in the case of functionalized ionic liquids, specific interactions. This model is not sufficient to obtain values of ET(30) quantitatively comparable to the experimental ones, but some qualitative features can be rationalized. The resulting scenario of solute–solvent interactions is different with respect to molecular solvents. Thus, we suggest caution in comparing ionic and molecular solvents through solvatochromic scales.     

Vaporization and thermal decomposition of B,B′,B″-tribromoborazine

Vapor pressure as a function of temperature above solid and liquid (BrBNH)₃ and the thermodynamic parameters of (BrBNH)₃ sublimation and vaporization have been determined using static tensimetry with membrane null-manometer. The thermal decomposition of tribromoborazine has been studied in the saturated and unsaturated vapor regions. Irreversible decomposition occurred at noticeable rates at temperatures higher than 343 K and was accompanied by HBr evolution. In the unsaturated vapor region, thermal decomposition has far lower rates than in the saturated vapor region because of diffusion limitations. The activation energy of condensed-phase thermal decomposition of B,B′,B″-tribromoborazine is 65 ± 3 kJ/mol, and this value proves that tribromoborazine decomposition at low temperatures is not accompanied by opening of the boron-nitrogen cycle.     

Convergence of Newton’s method under Vertgeim conditions: new extensions using restricted convergence domains

We present new sufficient convergence conditions for the semilocal convergence of Newton’s method to a locally unique solution of a nonlinear equation in a Banach space. We use Hölder and center Hölder conditions, instead of just Hölder conditions, for the first derivative of the operator involved in combination with our new idea of restricted convergence domains. This way, we find a more precise location where the iterates lie, leading to at least as small Hölder constants as in earlier studies. The new convergence conditions are weaker, the error bounds are tighter and the information on the solution at least as precise as before. These advantages are obtained under the same computational cost. Numerical examples show that our results can be used to solve equations where older results cannot.     

Mössbauer study on thermal decomposition of some hydroxy iron(III) carboxylates

Thermal decomposition of some hydroxy iron(III) carboxylates, i.e., iron(III) lactate, Fe(CH₃CHOHCOO)₃, iron(III) tartrate, Fe₂(C₄H₄O₆)₃ and iron(III) citrate, Fe(C₆H₅O₇) · 5H₂O has been studied in static air atmosphere in the temperature range 298–773 K employing Mössbauer, infrared spectroscopies and themogravimetric methods. The compounds directly decompose to -Fe₂O₃ without undergoing reduction to iron(II) intermediates. An increase in particle size of -Fe₂O₃ has been observed with increasing decomposition temperature. The thermal stability follows the sequence: iron(III) tartrate > iron(III)citrate > iron(III)lactate.     

Synthesis and thermal decomposition of 3,3’-bis-azidomethyl oxetane-3-azidomethyl-3’-methyl oxetane random copolymer

We synthesized a 3,3’-bis-azidomethyl oxetane-3-azidomethyl-3’-methyl oxetane random copolymer [poly(BAMO-r-AMMO)] using the borontrifluoride-dimethyl ether complex/diol initiator system. Hydrogen nuclear magnetic resonance (¹H NMR) was used to analyze the composition of the synthesized copolymer. The results indicated that the composition of the copolymer is in accordance with the molar feed ratio of the monomers. Thermogravimetric analysis (TGA) was used to study the thermal decomposition behavior. The main weight loss step in poly(BAMO-r-AMMO) coincides with the exothermic dissociation of the azido groups in the side chain. In poly(BAMO-r-AMMO), it appears that the other weight loss step is due to the decomposition of the polymer backbone. Kinetic analysis was performed by Vyazovkin’s model-free method. Based on the activation energy data, the random copolymer should form a reticular structure with chemical cross-linking points after the exothermic dissociation of the azido group. Using simultaneous TG-IR-MS data, it was confirmed that this process is controlled by the competitive reactions of intramolecular cyclization and intermolecular cross-linking.     

Mössbauer and infrared study of the thermal decomposition of iron and nickel compounds impregnated in alumina

In this work, studies of Fe₃(CO)₁₂ and a mixture of Fe₃(CO)₁₂ and Ni (acac)₂ impregnated in Al₂O₃ were undertaken using Mössbauer and i.r. spectroscopies. In freshly prepared samples, low oxidation species were shown to be present. After thermal decomposition, the data indicate the appearance of aluminum compounds of Fe^II and Fe^III plus superparamagnetic Fe^III. No Fe° species were detected, even under H₂ atmosphere.     

TG–DSC–FTIR–MS study of gaseous compounds evolved during thermal decomposition of styrene-butadiene rubber

The thermal decomposition behavior of styrene-butadiene rubber was studied using a system equipped with thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, and mass spectroscopy. Two different experiments were conducted. From these experiments, thermogravimetric analysis results indicated a mass loss of 58 % in the temperature range of ~290–480 °C and a mass loss of 39 % in the temperature range beyond 600 °C. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed the presence of oxides, even at 1,000 °C, accounting for the Zn, Mg, Al, Si, and Ca in the original sample.     

Kinetics of thermal dehydration and decomposition of Fe(III) chloride hydrate (FeCl3·xH 2O)

Fe(III) chloride hydrate (FeCl₃·xH₂O) undergoes simultaneous dehydration and dehydrochlorination from its molten phase in the temperature range 100–200C. The kinetics of these two parallel thermal processes has been studied by both isothermal and non-isothermal methods. Whereas for the dehydration reaction at temperature below 125C a second order rate model (F₂) fits well, a three-dimensional diffusion (D₃) model is found to fit better at temperature above 135C. For the dehydrochlorination reaction an interface growth controlled model of 1/3 order (F 1/3) appears to be the most suitable over a wide range of reaction. Dynamic thermogravimetry reveals two major steps in the temperature range 50–250C. The first step which corresponds to the loss of about 4 mols of H₂O, invariably follows second order kinetics (F₂). The second step which is predominantly a process of dehydrochlorination, generally fits mixed diffusion controlled models due to the overlapping with the dehydration process. There is an excellent agreement in results among the isothermal and non-isothermal methods of determining kinetic parameters.The authors are thankful to the Director, R. R. L. Bhubaneswar for his kind permission to publish this paper. One of the authors (SKM) is grateful to the Council of Scientific and Industrial Research, New Delhi, for the award of a Research Fellowship.     

Decomposition study of Ni–La–Mg–O precursors using thermal analysis

The thermal decomposition process of La₂O₃/MgO (La/Mg = 2, 1 and 0.5) supported nickel (15% mass/mass Ni) precursor was investigated. Thermal analysis results show distinct processes of decomposition of the samples in accordance with the composition. The mass loss at higher temperature is associated to distinct stages of decomposition of lanthanum precursors. The thermal analysis results agree with the FTIR spectra showing change in the band corresponding to carbonates and nitrates species. XRD results also confirmed the precursor’s decomposition. It can be concluded that the thermal decomposition of La₂O₃–MgO-nickel precursor depends on the La/Mg ratio and of the residual species.     

Copper-catalyzed trifluoromethylation of terminal alkynes using Umemoto’s reagent

A copper-catalyzed method for trifluoromethylation of terminal alkynes with Umemoto’s reagent has been developed. The reaction is conducted at room temperature and shows good tolerance to a variety of functional groups.     

Determination of Henry’s constant using a photoacoustic sensor

We present a simple method for measuring Henry’s constant k_Hof ethanol using photoacoustic spectroscopy. At T =  298.1 K the measured value fork_H is (0.877  ±  0.039)kPa · kg · mol ^− 1. Our data show that Henry’s law is valid at ethanol molalities between 0.1mol · kg ^− 1 and 1.4 mol · kg ^− 1. The temperature dependence of Henry’s constant was carefully examined by measuring the ethanol vapour pressure of six different aqueous solutions between T =  273.1 K and T =  298.1 K. By analysing the gas phase concentration and applying Henry’s law, an ethanol molality of 0.864 mol · kg ^− 1in the liquid phase can be measured with an error of  ± 0.038mol · kg ^− 1. The detection limit of the photoacoustic sensor is a gaseous ethanol pressure of 10 ^− 3kPa. Ethanol molality changes as low as 1.10 ^− 3mol · kg ^− 1can be measured.