Studies on the kinetics of racemization of 2,4-disubstituted-5(4H)-oxazolones

1988 ◽  
Vol 66 (10) ◽  
pp. 2540-2544 ◽  
Author(s):  
Marek Slebioda ◽  
Marc A. St-Amand ◽  
Francis M. F. Chen ◽  
N. Leo Benoiton
Keyword(s):  
Nitrogen Atom ◽  
Tertiary Amine ◽  
Thermodynamic Data ◽  
Activation Parameters ◽  
Steric Effects ◽  
Tertiary Amines ◽  
Electronic Effects ◽  
Catalyzed Reactions ◽  
Kinetics Of ◽  
Benzyl Substituent

The kinetics of racemization of 2,4-disubstituted-5(4H)-oxazolones obtained from N-acetyl, N-benzoyl, and N-benzyloxycarbonylglycyl-L-leucine, -valine, and -phenylalanine have been studied in several solvents alone and in the presence of tertiary amines. The influence of the nature of the substituents on the rate of the reaction has been evaluated, and the values of the activation parameters ΔH≠ and ΔS≠ for the base-catalyzed reactions have been determined. The racemization process is governed by electronic effects of the C(2)-substituents and steric effects of the C(4)-substituents of the oxazolones. The thermodynamic data suggest that the 2-substituted-4-benzyl-5(4H)-oxazolones racemize more readily than the 4-alkyl analogues (alkyl ≠ benzyl) because of the unique conformation assumed by the benzyl substituent. The rate of the base-catalyzed reaction depends on the extent of hindrance about the nitrogen atom of the tertiary amine as well as on its basicity. The data suggest that the relative rates of racemization of oxazolones are not a true reflection of the relative tendencies to racemize of the pertinent residues during couplings of the parent acids.

Studies on the decomposition of tetra-alkylammonium salts in solution. Part II. Dependence of the activation parameters on the structure of the substrate

1969 ◽  
Vol 47 (20) ◽  
pp. 3725-3728 ◽  
Author(s):  
J. T. Burns ◽  
K. T. Leffek
Keyword(s):  
Free Energy ◽  
Nitrogen Atom ◽  
Tertiary Amine ◽  
Chloroform Solution ◽  
Activation Parameters ◽  
Decomposition Reaction ◽  
Energy Correlation ◽  
Entropy Of Activation ◽  
Alkylammonium Salts ◽  
Enthalpy And Entropy

The enthalpy and entropy of activation for the decomposition reaction of seven tetra-alkylammonium iodides in chloroform solution have been measured. All the salts contained the benzyl group attached to the nitrogen atom and decomposed to yield benzyl iodide and a tertiary amine as the only products.A Hammett free energy correlation is made and used to deduce the nature of the transition state, and a rationalization of the variation of the enthalpy and entropy of activation with the structure of the substrate is given.

Kinetics of alkaline hydrolysis of mono- and dimethyl esters of 2,3- and 3,4-thiophenedicarboxylic acids, cyanothiophenecarboxylic acids and their dihydroanalogues

1987 ◽  
Vol 52 (8) ◽  
pp. 2005-2018
Author(s):  
Milan Struhárik ◽  
Pavel Hrnčiar ◽  
Dušan Loos
Keyword(s):  
Kinetic Parameters ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Activation Parameters ◽  
Hydrolysis Rate ◽  
Electronic Effects ◽  
Cyclic System ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Reactivity Order

Kinetics of alkaline hydrolysis of mono- and dimethyl esters of 2,3- and 3,4-thiophenedicarboxylic acids and their dihydroanalogues have been studied in 70% dioxane. The rate measurements have been carried out by the titrimetric method and the k1, k2 rate constants evaluated by the Frost-Schwemer method. The activation parameters of these reactions have been calculated. The results are compared with kinetic parameters of alkaline hydrolysis of methyl and dimethyl phthalates. The hydrolysis rate is significantly affected by the cyclic system to which the methoxycarbonyl groups are bound, the reactivity order being: Dihydrothiophene > thiophene > benzene. Also measured were the kinetics of alkaline hydrolyses of methyl 4-cyano-3-thiophenecarboxylate and 3-cyano-2-thiophenecarboxylate and of their dihydroanalogues. No meaningful preference of the hydrolysis of the group at the position 2 has been observed in case of 2,3-isomers. However, it has been confirmed that the hyper- and hypo-ortho transfer of electronic effects operates in the thiophene nucleus.

Dissociation kinetics of metal complexes in acid. II. Copper complexes of linear polyamines

1983 ◽  
Vol 36 (3) ◽  
pp. 433 ◽  
Author(s):  
DC Weatherburn
Keyword(s):  
Nitrogen Atom ◽  
Copper Complexes ◽  
Activation Parameters ◽  
Decomposition Kinetics ◽  
Acid Decomposition ◽  
Dissociation Kinetics ◽  
Rate Determining Step ◽  
Kinetics Of ◽  
Nitrogen Bond ◽  
Chelate Rings

The acid decomposition kinetics of the monocopper complexes of 20 different linear polyamines have been studied over a range of acid concentrations (0.025 to 0.5 mol dm-3), I 1.0 (NaNO3). Complexes which contain only six-membered chelate rings reacted at a rate which is independent of acid concentration. Complexes with five-membered chelate rings have rate constants which show a non-linear dependence on H+ concentration. Activation parameters have been determined for some complexes. A mechanism, in which the breaking of the first copper-nitrogen bond or the subsequent protonation of the nitrogen atom is the rate-determining step, is proposed.

THE KINETICS OF THE TERTIARY-AMINE-CATALYZED REACTION OF ORGANIC ISOCYANATES WITH THIOLS

1960 ◽  
Vol 38 (12) ◽  
pp. 2418-2424 ◽  
Author(s):  
Yoshio Iwakura ◽  
Hisao Okada
Keyword(s):  
Reaction Mechanism ◽  
Tertiary Amine ◽  
Relative Rate ◽  
Catalytic Action ◽  
Tertiary Amines ◽  
First Order ◽  
Kinetics Of

The kinetics of the reactions of isocyanates with thiols in the presence of tertiary amines were examined. The rate of the reaction was of the first order with respect to the concentration of isocyanate, thiol, and tertiary amine. The catalytic action of tertiary amines decreased in the order of triethylenediamine, triethylamine, diethylcyclohexylamine, tributylamine, N-methylmorpholine, pyridine, and quinoline. The relative rate of the reaction of phenylisocyanate with thiols decreased in the order of phenylmethanethiol, 1,4-butanedithiol, 1-butanethiol, 1-dodecanethiol, and thiophenol. The reaction took place more smoothly in strong ionizing solvents. These facts can be explained by the reaction mechanism indicated by the equations [6] to [8].

Substituent and steric effects in the oxidation of alkyl aryl sulfides by peroxydisulfate

1978 ◽  
Vol 56 (24) ◽  
pp. 3043-3046 ◽  
Author(s):  
C. Srinivasan ◽  
P. Kuthalingam ◽  
N. Arumugam
Keyword(s):  
Aqueous Ethanol ◽  
Activation Parameters ◽  
Steric Effects ◽  
Reaction Site ◽  
Electrophilic Attack ◽  
Alkyl Aryl ◽  
Kinetics Of Oxidation ◽  
Potassium Peroxydisulfate ◽  
Aryl Sulfides ◽  
Kinetics Of

The kinetics of oxidation of a number of alkyl aryl sulfides with potassium peroxydisulfate in aqueous ethanol have been investigated. The effect of substituents on the oxidation has been studied by employing a number of p- and m-substituted phenyl methyl sulfides: the reaction is accelerated by electron-releasing and retarded by electron-withdrawing substituents, indicating a rate-determining electrophilic attack by the peroxydisulfate ion at the reaction site, sulfur. A good correlation is found to exist between the rate constants and the Hammett σ+/σ− constants, the ρ+ value for the reaction being −0.56 with a correlation coefficient of 0.979. The activation parameters have also been determined.Studies with different alkyl phenyl sulfides clearly indicate that the reaction is quite sensitive to steric congestion around the reaction site. The results obtained in this study are compared with those found for the oxidation of the same set of sulfides with different oxidants.

Thermodynamic and Kinetic Investigation of the Solvent Effect on the Oxidation of [Co(en)2SCH2COO]+ with S2O82- In Water-Methanol and Water-tert-Butyl Alcohol Mixtures

1993 ◽  
Vol 58 (5) ◽  
pp. 1001-1006 ◽  
Author(s):  
Oľga Vollárová ◽  
Ján Benko
Keyword(s):  
Transfer Functions ◽  
Activation Parameters ◽  
Butyl Alcohol ◽  
Oxidation Of Co ◽  
Kinetics Of Oxidation ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Alcohol Mixtures ◽  
Kinetics Of

The kinetics of oxidation of [Co(en)2SCH2COO]+ with S2O82- was studied in water-methanol and water-tert-butyl alcohol mixtures. Changes in the reaction activation parameters ∆H≠ and ∆S≠ with varying concentration of the co-solvent depend on the kind of the latter, which points to a significant role of salvation effects. The solvation effect on the reaction is discussed based on a comparison of the transfer functions ∆Ht0, ∆St0 and ∆Gt0 for the initial and transition states with the changes in the activation parameters accompanying changes in the CO-solvent concentration. The transfer enthalpies of the reactant were obtained from calorimetric measurements.

Kinetics and Mechanism of Hexachloroiridate(IV) Oxidation of Arsenic(III) in Acidic Perchlorate Solutions

1992 ◽  
Vol 57 (7) ◽  
pp. 1451-1458 ◽  
Author(s):  
Refat M. Hassan
Keyword(s):  
Ionic Strength ◽  
Fractional Order ◽  
Activation Parameters ◽  
Order Reaction ◽  
First Order Reaction ◽  
Intermediate Complex ◽  
Constant Ionic Strength ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Kinetics Of

The kinetics of oxidation of arsenic(III) by hexachloroiridate(IV) at lower acid concentrations and at constant ionic strength of 1.0 mol dm-3 have been investigated spectrophotometrically. A first-order reaction in [IrCl62-] and fractional order with respect to arsenic(III) have been observed. A kinetic evidence for the formation of an intermediate complex between the hydrolyzed arsenic(III) species and the oxidant was presented. The results showed that decreasing the [H+] is accompanied by an appreciable acceleration of the rate of oxidation. The activation parameters have been evaluated and a mechanism consistent with the kinetic results was suggested.

Kinetics and mechanism of the reaction of iron(III) with 6-methyl-2,4-heptanedione and 3,5-heptanedione

1990 ◽  
Vol 55 (8) ◽  
pp. 1984-1990 ◽  
Author(s):  
José M. Hernando ◽  
Olimpio Montero ◽  
Carlos Blanco
Keyword(s):  
Aqueous Solution ◽  
Metal Ion ◽  
Activation Parameters ◽  
Enol Form ◽  
Kinetics And Mechanism ◽  
Kinetic Constants ◽  
Steric Factors ◽  
Kinetics Of ◽  
Mechanism Of The Reaction

The kinetics of the reactions of iron(III) with 6-methyl-2,4-heptanedione and 3,5-heptanedione to form the corresponding monocomplexes have been studied spectrophotometrically in the range 5 °C to 16 °C at I 25 mol l-1 in aqueous solution. In the proposed mechanism for the two complexes, the enol form reacts with the metal ion by parallel acid-independent and inverse-acid paths. The kinetic constants for both pathways have been calculated at five temperatures. Activation parameters have also been calculated. The results are consistent with an associative activation for Fe(H2O)63+ and dissociative activation for Fe(H2O)5(OH)2+. The differences in the results for the complexes of heptanediones studied are interpreted in terms of steric factors.

Configuration on the C=N double bond of monosubstituted amidines and amidoximes

1989 ◽  
Vol 54 (12) ◽  
pp. 3245-3252 ◽  
Author(s):  
Bernard Tinant ◽  
Janine Dupont-Fenfau ◽  
Jean-Paul Declercq ◽  
Jaroslav Podlaha ◽  
Otto Exner
Keyword(s):  
Double Bond ◽  
Nitrogen Atom ◽  
Steric Effects ◽  
Model Compounds ◽  
X Ray ◽  
Analogous Model

Configuration on the C=N double bond of amidines and amidoximes is controlled by steric effects on the second nitrogen atom but there is a difference in the case of N’-monosubstituted derivatives: amidines prefer E configuration (conformation around the C-N bond sp) and amidoximes Z configuration (conformation ap). This was confirmed by the X-ray structures of two analogous model compounds N,N’-dimethyl-4-nitrobenzamidine (monoclinic, P21c, a = 10.855(3), b = 11.043(3), c = 8.593(3) Å, β = 105.69(2)°, V = 991.8(5) Å3, Z = 4, Dx = 1.29 g cm-3, CuKα, λ = 1.5418 Å, μ = 7.91 cm-1, F(000) = 408, T = 291 K, R = 0.065 for 1 265 observed reflections) and N’-methyl-4-nitrobenzamidoxime (monoclinic, P21/a, a = 6.699(2), b = 24.178(9), c = 6.075(2) Å, β = 106.20(3)°, V = 944.9(6) Å3, Z = 4, Dx = 1.37 g cm-3, CuKα, λ = 1.5418 Å, μ =9.22 cm-1, F(000) = 408, T = 291 K, R = 0.079 for 1 278 observed reflections).

In-situ stabilization of silver nanoparticles in polymer hydrogels for enhanced catalytic reduction of macro and micro pollutants

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Luqman Ali Shah ◽  
Rida Javed ◽  
Mohammad Siddiq ◽  
Iram BiBi ◽  
Ishrat Jamil ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Thermo Gravimetric Analysis ◽  
Activation Parameters ◽  
Reduction Reaction ◽  
Gravimetric Analysis ◽  
X Ray Diffraction ◽  
In Situ Stabilization ◽  
Hybrid Hydrogels ◽  
Kinetics Of

AbstractThe in-situ stabilization of Ag nanoparticles is carried out by the use of reducing agent and synthesized three different types of hydrogen (anionic, cationic, and neutral) template. The morphology, constitution and thermal stability of the synthesized pure and Ag-entrapped hybrid hydrogels were efficiently confirmed using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). The prepared hybrid hydrogels were used in the decolorization of methylene blue (MB) and azo dyes congo red (CR), methyl Orange (MO), and reduction of 4-nitrophenol (4-NP) and nitrobenzene (NB) by an electron donor NaBH4. The kinetics of the reduction reaction was also assessed to determine the activation parameters. The hybrid hydrogen catalysts were recovered by filtration and used continuously up to six times with 98% conversion of pollutants without substantial loss in catalytic activity. It was observed that these types of hydrogel systems can be used for the conversion of pollutants from waste water into useful products.

Sign in / Sign up

Export Citation Format

Share Document