Existence Of Compensation Effect Research Articles

Synthesis, characterization and thermal decomposition of ethyl-2’-amino-5’-cyano-6’-(1H-indole-3yl)-2-oxospiro[indoline-3,4’-pyran]-3’-carboxylate under non‐isothermal condition in nitrogen atmosphere

A new compound, spiro-oxindole derivative compound namely ethyl-2ʹ-amino-5ʹ-cyano-6ʹ-(1H-indole-3yl)-2-oxospiro[indoline-3,4ʹ-pyran]-3ʹ-carboxylate (EACIOIPC) has been synthesized and characterized by microanalysis, FT-IR, mass spectrum and NMR (1H and 13C) techniques. The thermal decomposition of the compound was studied by thermogravimetric analysis under dynamic nitrogen atmosphere at different heating rates of 10, 15, 20 and 30 K/min. The kinetic parameters were calculated using model-free (Friedman’s, Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods) and model-fitting (Coats and Redfern (CR)) methods. The decomposition process of EACIOIPC followed a single step mechanism as evidenced from the data. Existence of compensation effect is noticed for the decomposition of EACIOIPC. Invariant kinetic parameters are consistent with the average values obtained by Friedman and KAS in conversional methods.

Structural effects and thermal decomposition kinetics of chalcones under non-isothermal conditions

Two chalcones namely, 1,5-bis(4-hydroxy-3-methoxyphenyl)pentan-1,4-dien-3-one (BHMPD) and 2,5-bis(4-hydroxy-3-methoxybenzylidene)cyclopentanone (BHMBC) have been synthesised and characterized by microanalysis, FT-IR, mass spectra and NMR (1H and 13C) techniques. The thermal decomposition of these compounds was studied by TGA and DTA under dynamic nitrogen atmosphere at different heating rates of 10, 15 and 20Kmin−1. The kinetic parameters were calculated using model-fitting (Coats–Redfern, CR) and model-free methods (Friedman, Kissinger–Akahira–Sunose, KAS and Flynn–Wall–Ozawa, FWO). The decomposition process of BHMPD and BHMBC followed a single step mechanism as evidenced from the data. Existence of compensation effect was noticed for the decomposition of these compounds. Invariant kinetic parameters are consistent with the average values obtained by Friedman and KAS isoconversional method in both compounds.

Reactivity of α-amino acids in the N-acylation with benzoic acid esters in aqueous dioxane

The effect of the nitro group as a substituent in the phenoxide part of phenyl benzoate on the rate of N-acylation of glycine, L-proline, and L-valine in the water (40 wt %)-dioxane solvent was studied. The activation parameters of glycine reactions with the esters were measured. The existence of compensation effect and the linear relation of the logarithms of the acylation constants to the Hammett constants were revealed. The energy of the LUMO of esters can serve as the descriptors of the easters reactivity.

Application of model-fitting and model-free kinetics to the study of non-isothermal dehydration of equilibrium swollen poly (acrylic acid) hydrogel: Thermogravimetric analysis

The dehydration kinetics of equilibrium swollen poly (acrylic acid) hydrogel is analyzed by both model-fitting and model-free approaches. The conventional model-fitting approach assuming a fixed mechanism throughout the reaction and extract a single values of the apparent activation energy ( E a) and pre-exponential factor ( A) and was found to be too simplistic. The values of Arrhenius parameters obtained in such a way are in fact an average that does not reflect changes in the reaction mechanism and kinetics with the extent of conversion. The model-free approach allows for a change of mechanism and activation energy, E a, during the course of a reaction and is therefore more realistic. The complexity of the dehydration of poly (acrylic acid) hydrogel is illustrated by the dependence of E a and A on the extent of conversion, α (0.05 ≤ α ≤ 0.98). Under non-isothermal conditions, E a decreases with α for 0 ≤ α ≤ 0.50, followed by an approximately constant value of E a during further dehydration. For 0 ≤ α ≤ 0.50, dehydration is complex, which probably involving a combination of several processes. In the constant- E a region, non-isothermal dehydration follows the three-dimensional phase boundary model (R3). The complex hydrogen-bond pattern in poly (acrylic acid) hydrogel is probably responsible for the observed dehydration behavior. An existence of compensation effect is accepted and explanation of compensation effect appearance during the hydrogel dehydration is suggested.

Kinetics and mechanism of isatin ring opening in aqueous binary mixtures of methanol and acetonitrile cosolvents

Solvent effects on the kinetics of hydrolysis of isatin by sodium hydroxide have been investigated within the temperature range (30–55°C) in methanol-water and acetonitrile-water media of varying solvent compositions up to 70% (v/v) of the organic solvent component. The thermodynamic activation parameters were calculated and discussed in terms of solvation effects. The determined isokinetic temperatures, in both systems, revealed the existence of compensation effect arising from strong solute-solvent interactions; log k was correlated with both log [H2O] and the reciprocal of the dielectric constant. The first correlation was observed to be linear while the second was nonlinear. Finally a mechanism for the isatin ring opening was proposed, which accounts for the role and the effect of the solvent on the reaction rate. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 463–469, 1998

Compensation effect in mixtures of organic semiconductors

Results obtained with mechanical mixtures of two chemically stable and non-interacting organic semiconductors confirm the validity of the compensation effect. For the specific conductivity value and its activation energy in mixtures the generalized Lichtenecker's "logarithmic mixing rule" applies; from this immediately follows the existence of compensation effect. This general phenomenon may in some cases be responsible for the existence of compensation effect described in the literature.