Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

scholarly journals Kinetics and Mechanism of Oxidation of Diethanolamine and Triethanolamine by Potassium Ferrate

2011 ◽  
Vol 8 (2) ◽  
pp. 903-909 ◽  
Author(s):  
Shan Jinhuan ◽  
Zhang Jiying
Keyword(s):  
Activation Parameters ◽  
Rate Equations ◽  
Potassium Ferrate ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Order Dependence ◽  
Rate Determining Step ◽  
Thermodynamic Activation Parameters ◽  
Plausible Mechanism ◽  
Kinetics Of

The kinetics of oxidation of diethanolamine and triethanolamine by potassium ferrate(VI)in alkaline liquids at a constant ionic strength has been studied spectrophotometrically in the temperature range of 278.2K-293.2K. The reaction shows first order dependence on potassium ferrate(VI), first order dependence on each reductant, The observed rate constant (kobs) decreases with the increase in [OH-], the reaction is negative fraction order with respect to [OH-]. A plausible mechanism is proposed and the rate equations derived from the mechanism can explain all the experimental results. The rate constants of the rate-determining step and the thermodynamic activation parameters are calculated.

Kinetic Studies of Gold Recovery from Diluted Chloride Aqueous Solutions Using Activated Carbon Organosorb 10 CO

2016 ◽  
Vol 69 (3) ◽  
pp. 254 ◽  
Author(s):  
Marek Wojnicki ◽  
Ewa Rudnik ◽  
Magdalena Luty-Błocho ◽  
Robert P. Socha ◽  
Zbigniew Pędzich ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Acidic Solution ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Reaction Model ◽  
Surface Functional Groups ◽  
Complex Ions ◽  
First Order ◽  
Material Theory

The kinetic studies of gold(iii) chloride complex ions recovery from acidic solution using activated carbon (AC) were carried out using spectrophotometry. AC samples were characterized in terms of surface area, porosity, and zeta potential. The surface functional groups were also identified. It was found that adsorption of AuCl4– onto AC was followed by reduction of the ions to the metallic form. The process obeyed the first order reaction model, but the reaction was controlled by diffusion. Arrhenius and Eyring–Polanyi equations were used for determination of the activation parameters. Distribution of gold across the AC pellets was also determined and discussed according to the porous material theory.

Mutarotation of some biologically important 2-substituted hexoses

1974 ◽  
Vol 337 (1610) ◽  
pp. 317-332 ◽  
Keyword(s):  
Acetic Acid ◽  
Transition State ◽  
Rate Constants ◽  
Activation Parameters ◽  
Water Molecules ◽  
Concerted Mechanism ◽  
Hydronium Ion ◽  
Thermodynamic Activation Parameters

Catalysis by water, hydronium ion, acetate ion, acetic acid, pyridine and 3-hydroxypyridine of the mutarotation of D-glucose, 2-deoxy-D-glucoso, 2-amino-2-deoxy-D-glucose and 2-acetamido-2-deoxy-n-glucose has been studied polarimetrically. Rate constants were measured at 298 and 308 K and the thermodynamic activation parameters have been calculated for each case. It is concluded that the mutarotation reaction probably takes place by a concerted mechanism in which two or more water molecules are involved in the transition state.

scholarly journals Effect of heparin on thrombin inactivation by antithrombin-III

1978 ◽  
Vol 173 (3) ◽  
pp. 869-875 ◽  
Author(s):  
R Machovich ◽  
P Arányi
Keyword(s):  
Antithrombin Iii ◽  
Specific Activity ◽  
Activation Parameters ◽  
Heat Inactivation ◽  
Activation Entropy ◽  
First Order ◽  
Heparin Concentration ◽  
First Order Kinetics ◽  
Thermodynamic Activation Parameters ◽  
Time Courses

The inactivation of thrombin by heat and by its physiological inhibitor, antithrombin-III, shows quite different dependence on heparin concentration. Heparin at 250 microgram/ml protects thrombin against heat inactivation, and thrombin behaves heterogeneously in this reaction. In the absence of heparin, the thermodynamic activation parameters change with temperature (deltaH+ = 733 kJ/mol and 210 kJ/mol at 50 and 58 degrees C respectively). When heparin is present, heat inactivation of the protected thrombin species proceeds with deltaH+ = 88 kJ/mol and is independent of temperature in the same range. On the other hand, heparin at 0.125-2.5 microgram/ml accelerates the thrombin-antithrombin-III reaction. Thrombin does not show heterogeneity in this reaction and the time courses at any heparin concentration and any temperature between 0 and 37 degrees C appear to follow first-order kinetics. Activation enthalpy is independent of heparin concentration or temperature, deltaH+ = 82-101 kJ/mol, varying slightly with antithrombin-III concentration and thrombin specific activity. Heparin seems to exert its effect by increasing activation entropy. On the basis of these data we suggest a mechanism of action of heparin in the thrombin-antithrombin-III reaction which accounts for all the important features of the latter and seems to unify the different hypotheses that have been advanced.

scholarly journals Kinetics and Mechanism of Micellar Catalyzed Oxidation of Dextrose by N-Bromosuccinimide in H2SO4 Medium

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Minu Singh
Keyword(s):  
Fractional Order ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Kinetics And Mechanism ◽  
Stoichiometric Ratio ◽  
Product Analysis ◽  
Experimental Conditions ◽  
First Order ◽  
Order Dependence ◽  
Wide Range

Kinetics and mechanism of micellar catalyzed N-bromosuccinimide oxidation of dextrose in H2SO4 medium was investigated under pseudo-first-order condition temperature of 40°C. The results of the reactions studied over a wide range of experimental conditions show that NBS shows a first order dependence, fractional order, on dextrose and negative fractional order dependence on sulfuric acid. The determined stoichiometric ratio was 1 : 1 (dextrose : N-bromosuccinimide). The variation of Hg(OAC)2 and succinimide (reaction product) has insignificant effect on reaction rate. Effects of surfactants, added acrylonitrile, added salts, and solvent composition variation have been studied. The Arrhenius activation energy and other thermodynamic activation parameters are evaluated. The rate law has been derived on the basis of obtained data. A plausible mechanism has been proposed from the results of kinetic studies, reaction stoichiometry, and product analysis. The role of anionic and nonionic micelle was best explained by the Berezin’s model.

scholarly journals The carboxybiotin complex of chicken liver pyruvate carboxylase. A kinetic analysis of the effects of acetyl-CoA, Mg2+ ions and temperature on its stability and on its reaction with 2-oxobutyrate

1986 ◽  
Vol 235 (2) ◽  
pp. 359-364 ◽  
Author(s):  
P V Attwood ◽  
J C Wallace
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Protein Conformation ◽  
Pyruvate Carboxylase ◽  
Activation Parameters ◽  
Slow Phase ◽  
Acetyl Coa ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Pseudo First Order

The enzyme-[14C]carboxybiotin complex of chicken liver pyruvate carboxylase has been isolated and shown to be relatively stable, with a half-life at 0 degree C of 342 min. The kinetic properties of the decay of this complex, in both the presence and the absence of the substrate analogue, 2-oxobutyrate, have been examined. The data for the reaction with 2-oxobutyrate at 0 degree C fitted a biphasic exponential decay curve, enabling the calculation of rate constants for both the fast and slow phases of the reaction at this temperature. The effect of temperature on the observed pseudo-first-order rate constant for the slow phase of the reaction with 2-oxobutyrate, and that for the decay of the enzyme-[14C]carboxybiotin complex alone, have been examined. Arrhenius plots of these data revealed that the processes being studied in each type of experiment were single reactions represented by one rate constant in each case. For the decay of the enzyme-[14C]carboxybiotin complex in the absence of 2-oxobutyrate, the rate-determining process may be the movement of carboxybiotin from the site of the first partial reaction to the site of the second. The calculated thermodynamic activation parameters indicate that this reaction is accompanied by a large change in protein conformation. With 2-oxobutyrate present, the observed process in the slow phase of the reaction was probably the dissociation of the carboxybiotin from the first subsite. Here, the activation parameters suggest that a much smaller change in protein conformation accompanies this reaction. Both sets of experiments were also performed in the presence of acetyl-CoA, but this activator had little effect on the measured thermodynamic activation parameters. However, in both cases the observed pseudo-first-order rate constants in the presence of acetyl-CoA were about 75% of those in its absence. The effects of Mg2+ on the reaction kinetics of the enzyme-[14C]carboxybiotin complex with 2-oxobutyrate were similar to those observed with the sheep enzyme by Goodall, Baldwin, Wallace & Keech [(1981) Biochem. J. 199, 603-609].

scholarly journals Determination of the activation parameters ∆H≠ and ∆S≠ via a kinetic study of d,l-mandelic acid oxidation by using chromic acid in the presence of 1,10-phenanthroline as a promoter in an aqueous micellar acid medium

2021 ◽  
pp. 174751982110459
Author(s):  
Monirul Islam ◽  
Swarnava Singha ◽  
Anwesha Bhattacharyya ◽  
Debraj Roy
Keyword(s):  
Rate Constant ◽  
Mandelic Acid ◽  
Chromic Acid ◽  
Cetylpyridinium Chloride ◽  
Activation Parameters ◽  
Effect Of Temperature ◽  
Acid Oxidation ◽  
Cyclic Transition ◽  
First Order ◽  
Order Dependence

Chromic acid oxidation of d,l-mandelic acid in the presence and absence of 1,10-phenanthroline (Phen) is studied in an aqueous micellar medium under kinetic conditions, [d,l-mandelic acid] >> [Phen]T >> [Cr(VI)]T at different temperatures. From studies on the effect of temperature on the rate constant (k), the activation parameters ∆H≠ (enthalpy of activation) and ∆S≠ (entropy of activation) are evaluated by using the Eyring equation [−ln (kh/kBT) = ∆H≠/RT − ∆S≠/R]. The high value of ∆H≠ indicates that the phen-catalysed path is favoured mainly due to very high negative value of ∆S≠. The negative value of ∆S≠ and the composite rate constant kcat support the suggested cyclic transition state. Both the catalysed and uncatalysed paths show a first-order dependence on [H+], and both also show a first-order dependence on [d,l-mandelic acid]T and [Cr(VI)]T. The Phen-catalysed path is first order in [Phen]T. These observations remain unaltered in the presence of externally added surfactants. The cationic surfactant N-cetylpyridinium chloride is found to retard the rate of the reaction.

scholarly journals A kinetic study of Zn halide/TBAB-catalysed fixation of CO2 with styrene oxide in propylene carbonate

2019 ◽  
Vol 8 (1) ◽  
pp. 719-729 ◽  
Author(s):  
Abdul Rehman ◽  
M.F.M. Gunam Resul ◽  
Valentine C. Eze ◽  
Adam Harvey
Keyword(s):  
Propylene Carbonate ◽  
Styrene Oxide ◽  
Activation Parameters ◽  
Green Solvent ◽  
Acid Base ◽  
First Order ◽  
First Order Kinetics ◽  
Thermodynamic Activation Parameters ◽  
Styrene Carbonate ◽  
Comprehensive Study

Abstract Synthesis of styrene carbonate (SC) via the fixation of CO2 with styrene oxide (SO) has been investigated using a combination of zinc bromide (ZnBr2) and tetrabutylammonium halides (TBAX) as acid-base binary homogeneous catalysts. The combination of ZnBr2 and TBAB had a synergistic effect, which led to about 6-fold enhancement in the rate of SC formation as compared to using TBAB alone as a catalyst. Propylene carbonate (PC) was chosen as a green solvent for a comprehensive study of reaction kinetics. The reaction followed a first-order kinetics with respect to SO, CO2, and TBAB, whereas a fractional order was observed for the ZnBr2 when used in combination with the TBAB. Arrhenius and Eyring’s expressions were applied to determine the kinetic and thermodynamic activation parameters, where activation energy (Ea) of 23.3 kJ mol−1 was obtained for the SC formation over the temperature range of 90-120°C. The thermodynamic analysis showed that positive values for enthalpy (ΔH‡ = 18.53 kJ mol−1), Gibbs free energy (ΔG‡ = 79.74 kJ mol−1), whereas a negative entropy (ΔS‡ = –162.88 J mol−1 K−1) was obtained. These thermodynamic parameters suggest that endergonic and kinetically controlled reactions were involved in the formation of SC from SO and CO2.

Solvent Effects on the Racemization of Optically Active Tris(N-substituted carbamodithioato)cobalt (III) Complexes

1979 ◽  
Vol 32 (8) ◽  
pp. 1653 ◽  
Author(s):  
LR Gahan ◽  
MJ O'Conner
Keyword(s):  
Carbon Tetrachloride ◽  
Solvent Effects ◽  
Reaction Mechanisms ◽  
Activation Parameters ◽  
Optically Active ◽  
Isokinetic Relationship ◽  
First Order ◽  
First Order Kinetics ◽  
Thermodynamic Activation Parameters ◽  
Wide Range

The thermal racemization in solution of some optically active tris(N-substituted carbamodithioato)- cobalt(III) complexes [N-substituents = diphenyl, dimethyl, diisopropyl, and tetramethylene (pyrrolidinyl)] has been measured polarimetrically in a range of solvents including dimethylformamide, acetonitrile, carbon tetrachloride, chlorobenzene, chloroform, toluene and ethanol. The metal-centred (Δ ↔ Λ) inversion reactions show first-order kinetics as expected for an intra- molecular process. Thermodynamic activation parameters for the reaction show that values of ΔS‡ occur over a wide range (from -124 to +60 J K-1 mol-1) as do the values of ΔH‡ (from 67�4 to 129�3 kJ mol-1). Values for ΔG‡ are reasonably constant. Although a similar mechanism for the metal-centred inversion is suggested for all compounds in the various solvents because of an observed isokinetic relationship between ΔH‡ and ΔS‡, with isokinetic temperatures in the range 312-369 K, it is clear that postulates of reaction mechanisms based on the value of ΔS‡ determined in only one solvent should be treated with caution. The optically active (-)546-tris(N,N-diisopropylcarbamodithioato)cobalt(III) complex photoracemizes in solution without decomposition. The rate of photoracemization is solvent-dependent being in the order bromoform � carbon tetrachloride ≈ chloroform �benzene.

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