Thermolysis of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones in solution. Products, kinetics, substituent effects, and solvent effects

1981 ◽  
Vol 59 (1) ◽  
pp. 100-105 ◽  
Author(s):  
Lubomira M. Cabelkova-Taguchi ◽  
John Warkentin
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Charge Separation ◽  
Substituent Effects ◽  
Activation Parameters ◽  
Oxidative Cyclization ◽  
First Order ◽  
Temperature Range ◽  
Aryl Amine ◽  
First Order Kinetics

A series of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones (Ar = C6H5, p-C6H4CH3, p-C6H4OCH3, p-C6H4Cl, and p-C6H4Br) were prepared from the corresponding 4-arylsemicarbazones of acetone by oxidative cyclization on alumina. The triazolinones decompose in solution to N2, CO, and isopropylidene aryl amine, with first order kinetics, in the temperature range 148–200 °C. Average activation parameters are ΔH≠ = 35 kcal mol−1 and ΔS≠ = 8 cal K−1 mol−1. Substituent effects are correlated through σ-constants but the thermolyses are relatively insensitive to substituents, with ρ = −0.17 at 172.5 °C. Solvent effects indicate a transition state that is less polar than the ground state.It is tentatively concluded that the triazolinone fragmentation, like the analogous thermolysis of a Δ3-1,3,4-oxadiazolin-2-one, may be a fully-concerted but nonsynchronous process with a transition state involving little, if any, charge separation. Other mechanisms, except for those involving highly polar (e.g. zwitterionic) transition states, have not been ruled out.

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.

The kinetics and the mechanism of oxidative decarboxylation of benzilic acid by acidic permanganate (stopped-flow technique) — An autocatalytic study

2004 ◽  
Vol 82 (9) ◽  
pp. 1372-1380 ◽  
Author(s):  
Sairabanu A Farokhi ◽  
Sharanappa T Nandibewoor
Keyword(s):  
Activation Parameters ◽  
Oxidative Decarboxylation ◽  
Two Stage ◽  
First Order ◽  
First Order Kinetics ◽  
Stage Process ◽  
Benzilic Acid ◽  
Reaction Constants ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of the oxidation of benzilic acid by potassium permanganate in an acidic medium were studied spectrophotometrically. The reaction followed a two-stage process, wherein both stages of the reaction followed first-order kinetics with respect to permanganate ion and benzilic acid. The rate of the reaction increased with an increase in acid concentration. Autocatalysis was observed by one of the products, i.e., manganese(II). A composite mechanism involving autocatalysis has been proposed. The activation parameters of the reaction were calculated and discussed and the reaction constants involved in the mechanisms were calculated. There is a good agreement between the observed and calculated rate constants under different experimental conditions.Key words: oxidation, autocatalysis, benzilic acid, two-stage kinetics.

Substituent effects on rates of formation of methoxy-substituted carbonyl ylides from 2-aryl-2-methoxy- and 5-aryl-2-methoxy-Δ3-1,3,4-oxadiazolines

1984 ◽  
Vol 62 (8) ◽  
pp. 1646-1652 ◽  
Author(s):  
Michel Békhazi ◽  
Peter J. Smith ◽  
John Warkentin
Keyword(s):  
Transition State ◽  
Electron Density ◽  
Rate Constants ◽  
Substituent Effects ◽  
Partial Identification ◽  
Trans Isomers ◽  
First Order Kinetics ◽  
Bond Scission ◽  
Carbonyl Ylide ◽  
Substituent Constants

2-Aryl-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines (4) and 5-aryl-2-methoxy-2,5-dimethyl-Δ3-1,3,4-oxadiazolines (5) were synthesized. Compounds 4 decompose in solution with first order kinetics. Rate constants are correlated with Hammett substituent constants (σ−) with ρ(49.2 °C) = 0.74 and 0.89 for CCl4, and CD3OD, respectively. The final products from 4 indicate that thermolysis involves the cleavage of both C—N bonds, to form N2 and, initially, a carbonyl ylide. Compounds 5, which were obtained as mixtures of cis/trans isomers containing several impurities, and which therefore gave poorer kinetic data, decomposed in CDCl3 solution with [Formula: see text] Carbonyl ylide intermediates, similar to those from the closelyrelated compounds 4, were assumed on the basis of analogy and on the basis of partial identification of products. The effects of para substituents in the aryl groups of 4 and 5 show that the transition states have greater electron density at C-2 of 4 and at C-5 of 5 than do the starting materials. In spite of the increase in electron density at C-2 of 4, the transition state must be less polar, overall, than the ground state because rate constants for thermolysis of 4 in methanol are smaller than those for CCl4, solvent. A plausible explanation for the substituent effects and the solvent effects is that the loss of N2 is concerted, with a transition state resembling more closely a spin paired 1,3-diradical than a 1,3-dipole. Alternative stepwise mechanisms, in which C2—N3 bond scission of 4 and C5—N4 bond scission of 5 are the rate-determining steps, leading to 1,5-diradical intermediates, can not be excluded on the basis of the evidence.

A thermal [1,3] sigmatropic rearrangement: thermolysis of 2,2-bis(ethylthio)-3,3-dimethyl-4-pentenal

1981 ◽  
Vol 59 (21) ◽  
pp. 3120-3122 ◽  
Author(s):  
Gordon S. Bates ◽  
S. Ramaswamy
Keyword(s):  
Solvent Effect ◽  
Wide Temperature Range ◽  
Sigmatropic Rearrangement ◽  
Positive Entropy ◽  
First Order ◽  
Temperature Range ◽  
First Order Kinetics ◽  
Sigmatropic Shift ◽  
Entropy Of Activation

2,2-Bis(ethylthio)-3,3-dimethyl-4-pentenal was found to quantitatively isomerize to 2,2-bis(ethylthio)-5-methyl-4-hexenal over a wide temperature range (130–170 °C). This rearrangement can formally be regarded as a [1,3] sigmatropic shift. The reaction, which could be conveniently monitored by 1Hmr spectroscopy, was found to obey first order kinetics. The substantial positive entropy of activation (+ 61.5 J deg−1 mol−1) for the reaction and the negligible solvent effect (decane vs. DMF) are both consistent with a proposed diradical pathway.

scholarly journals KINETICS OF REACTION BETWEEN MALACHITE GREEN AND HYDROXYL ION IN THE PRESENCE OF REDUCING SUGARS

2015 ◽  
Vol 23 (23) ◽  
pp. 61-72
Author(s):  
Dayo Felix Latona ◽  
Adewumi Oluwasogo Dada
Keyword(s):  
Malachite Green ◽  
Activation Parameters ◽  
Cell Compartment ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Hydroxyl Ion ◽  
Kinetics Of Reaction ◽  
Kinetics Of ◽  
Sphere Mechanism

The reaction was studied via pseudo-first-order kinetics using a UV-1800 Shimadzu spectrophotometer with a thermostated cell compartment and interfaced with a computer. The reaction showed first order with respect to malachite green and sugar and hydroxyl ion concentrations. However, the reaction was independent of ionic strength and showed no dependence on the salt effect, indicating an inner sphere mechanism for the reaction. There was no polymerization of the reaction mixture with acrylonitrile, indicating the absence of radicals in the course of the reaction. Michaelis-Menten plot indicated the presence of a reaction intermediate in the rate-determining step. The activation parameters of the reaction have been calculated and products were elucidated by FTIR spectroscopy. The stoichiometry of the reaction is 1:1. A mechanism consistent with the above facts has been suggested.

Kinetics of reactions of para-substituted phenyl isocyanates with amines and alcohols

1991 ◽  
Vol 56 (8) ◽  
pp. 1662-1670 ◽  
Author(s):  
Ivan Danihel ◽  
Falk Barnikol ◽  
Pavol Kristian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Stopped Flow ◽  
Partial Charges ◽  
Hammett Correlation ◽  
One Step ◽  
Kinetics Of

The reaction of para-substituted phenyl isocyanates with amines and alcohols was studied by stopped-flow method. The Hammett correlation obtained showed that the sensitivity of the above mentioned reactions toward substituent effects is the same as that of analogous reactions of phenyl isothiocyanates (ρ ~ 2). The rate constants of these reactions were found to be affected more by steric effects than by solvent effects. An one step multicentre mechanism with partial charges in transition state has been proposed for the title reactions.

scholarly journals Nonenzymatic NADH-Dependent Reduction of Keggin-Type 12-Tungstocobaltate(III) in Aqueous Medium

2011 ◽  
Vol 8 (3) ◽  
pp. 1152-1157
Author(s):  
Prabla Kumari ◽  
Alaka Das ◽  
Dillip Kumar Baral ◽  
A. K. Pattanaik ◽  
P. Mohanty
Keyword(s):  
Electron Transfer ◽  
Transition State ◽  
Aqueous Medium ◽  
Transfer Reaction ◽  
Activation Parameters ◽  
Electron Transfer Reaction ◽  
Transfer Reactions ◽  
Electron Transfer Reactions ◽  
First Order ◽  
Kinetics Of

The kinetics of the electron transfer reaction of NADH with 12-tungstocobaltate(III) has been studied over the range 5.07 ≤ 104[NADH] ≤ 15.22 mol dm-3, 7.0 ≤ pH ≤ 8.0 and 20 ≤ t ≤ 35oC in aqueous medium. The electron transfer reaction showed first-order dependence each in [NADH]Tand [12-tungstocobaltate(III)]T. The products of the reaction were found to be NAD+and 12-tungstocobaltate(II). The activation parameters ΔH#(kJ mol-1) and ΔS#(JK-1mol-1) of the electron transfer reactions were found to be 64.4±1.8 and -48.86±6.0. Negative value of ΔS#is an indicative of an ordered transition state for the electron transfer reaction.

Acetoxylation by aryliodoso acetates. II. Kinetics of the reaction of phenyliodoso acetate with aceto-p-toluidide

1958 ◽  
Vol 11 (1) ◽  
pp. 34
Author(s):  
WD Johnson ◽  
NV Riggs
Keyword(s):  
Acetic Acid ◽  
Acetic Anhydride ◽  
Transition State ◽  
Arrhenius Equation ◽  
First Order ◽  
Temperature Range ◽  
Polar Transition ◽  
Kinetics Of

The reaction of phenyliodoso acetate and aceto-p-toluidide in acetic acid is first order in each reactant and measured rates fit the Arrhenius equation in the temperature range 15-45 �C. Addition of water to the solvent markedly accelerates the reaction, whereas addition of benzene lowers the rate and acetic anhydride has little effect. A polar transition state is indicated.

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.

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