Kinetics and mechanism of oxidation of hydroxylamine by hexachloroiridate(IV) ion in buffer solutions

1993 ◽  
Vol 71 (12) ◽  
pp. 2164-2170 ◽  
Author(s):  
Ms. Rekha ◽  
Aditya Prakash ◽  
Raj N. Mehrotra
Keyword(s):  
Acetic Acid ◽  
Spectral Analysis ◽  
Rate Constants ◽  
Main Product ◽  
Activation Parameters ◽  
Acetate Buffer ◽  
Stopped Flow ◽  
Stoichiometric Ratio ◽  
Buffer Solutions ◽  
Mechanism Of Oxidation

The oxidation of hydroxylammonium ion by [IrCl6]2− ion in acetic acid – acetate buffer solutions, studied by stopped flow, has the stoichiometric ratio Δ[IrCl6]2−/Δ[NH2OH] = 1. The oxidation involves the species [IrCl6]2− and NH3OH+ although spectral analysis of the spent reaction mixture indicates [IrCl5(OH2)]2− to be the main product (almost to the extent of 80%). This anomaly arises because of the aquation of the reduced product [IrCl6]3−. The rate is retarded both by H+ and Cl− ions and the plots of [Formula: see text] against respective concentrations are linear. The proposed mechanism is given by reactions [i]–[v].[Formula: see text]The values of the rate constants at 25 °C are as follows: k1 = 147 dm3 mol−1 s−1 and 102ketKia = 2.8 s−1. The related activation parameters are [Formula: see text], and,[Formula: see text], and [Formula: see text] and [Formula: see text], respectively. The value of Kipd is 2.91 ± 0.03 mol dm−3 and that of Kipa (= 1/Kipd) is 0.344 ± 0.004 dm3 mol−1; both values are almost independent of temperature.

scholarly journals Kinetics and Mechanism of Oxidation of Tartaric Acid by N-Chloronicotinamide (NCN)

2015 ◽  
Vol 52 ◽  
pp. 120-125 ◽  
Author(s):  
L. Pushpalatha
Keyword(s):  
Acetic Acid ◽  
Tartaric Acid ◽  
Fractional Order ◽  
Rate Constants ◽  
Activation Parameters ◽  
First Order ◽  
First Order Kinetics ◽  
Different Temperatures ◽  
Mechanism Of Oxidation ◽  
Experimental Findings

The oxidation of tartaric acid by N-chloronicotinamide in the presence of HClO4 is studied. First order kinetics with respect to NCN is observed. The kinetics results indicate fractional order dependence about [tartaric acid]. Inverse first order in [nicotinamide] and inverse fractional order about [H+] are noted. Rate of the reaction increases with a decrease in the percentage of acetic acid. The values of rate constants observed at four different temperatures were utilized to calculate the activation parameters. A suitable mechanism consistent with the experimental findings has been proposed.

scholarly journals Kinetics and Mechanism of the Change of the 4-Nitrobenzylthio-System into 4,4′-Diformylazoxybenzene in Alkaline Dioxane-Water Media

1985 ◽  
Vol 40 (11) ◽  
pp. 1128-1132
Author(s):  
Y. Riad ◽  
Adel N. Asaad ◽  
G.-A. S. Gohar ◽  
A. A. Abdallah
Keyword(s):  
Acetic Acid ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Main Product ◽  
Reaction Medium ◽  
Aqueous Dioxane ◽  
Proton Abstraction ◽  
First Order ◽  
Water Media ◽  
Different Temperatures

Sodium hydroxide reacts with α -(4-nitrobenzylthio)-acetic acid in aqueous-dioxane media to give 4,4'-diformylazoxybenzene as the main product besides 4,4'-dicarboxyazoxybenzene and a nitrone acid. This reaction was kinetically studied in presence of excess of alkali in different dioxane-water media at different temperatures. It started by a fast reversible a-proton abstraction step followed by two consecutive irreversible first-order steps forming two intermediates (α -hydroxy, 4-nitrosobenzylthio)-acetic acid and 4-nitrosobenzaldehyde. The latter underwent a Cannizzaro's reaction, the products of which changed in the reaction medium into 4,4'-diformylazoxybenzene and 4,4'-dicarboxyazoxybenzene. The rate constants and the thermodynamic parameters of the two consecutive steps were calculated and discussed. A mechanism was put forward for the formation of the nitrone acid.Other six 4-nitrobenzyl, aryl sulphides were qualitatively studied and they gave mainly 4,4'-diformylazoxybenzene beside 4,4'-dicarboxyazoxybenzene or its corresponding azo acid.

Hydrogen Isotope Exchange in 2-Butanone. Further Measurements and Some Comments

1972 ◽  
Vol 50 (19) ◽  
pp. 3239-3241 ◽  
Author(s):  
R. A. Cox ◽  
J. W. Thorpe ◽  
J. Warkentin
Keyword(s):  
Acetic Acid ◽  
Temperature Dependence ◽  
Rate Constants ◽  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Relative Rate ◽  
Aqueous Media ◽  
Acetate Buffer ◽  
Isokinetic Temperature ◽  
Relative Rate Constants

The ratio of rate constants for exchange at the methylene and methyl positions of butanone, [Formula: see text], is shown to be near 1.69 in 1:1 acetic acid–acetate buffer; nearly twice the value (0.86) for deuterioxide catalysis at 54.8°. Methods of obtaining rate constants for acetate catalysis from composite rates (acetate and deuterioxide), or from rates in buffered media, are shown to be adequate for estimating rate ratios.Detailed temperature dependence of the relative rate constants for either system is not yet available but the effects are known to be small. For butanone enolizations the isokinetic temperature is in the neighborhood of 35°, when reaction is catalyzed by deuterioxide in aqueous media.

Kinetic studies of the reactions of 4-nitrobenzofuroxan with cyanide ion and isopropoxide ion in isopropanol

1980 ◽  
Vol 58 (16) ◽  
pp. 1691-1696 ◽  
Author(s):  
Michael E. Moir ◽  
Albert R. Norris
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Specific Rate ◽  
Stopped Flow ◽  
Cyanide Ion ◽  
Temperature Range ◽  
Flow Reaction

Kinetic studies of the reactions in isopropanol of 4-nitrobenzofuroxan with cyanide ion and isopropoxide ion have been carried out over the temperature range 15.0 to 35.0 °C. For both bases, the first species identifiable using stopped-flow reaction techniques is postulated to be a C-7 σ-complex of 4-nitrobenzofuroxan and base. Specific rate constants and activation parameters for the formation of these σ-complexes are compared to corresponding data relating to the formation of cyanide ion and isopropoxide ion—σ-complexes of 1,3,5-trinitrobenzene in isopropanol.

Kinetic and Mechanistic Study on the Reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ with L-Cysteine and S-Methyl-L-cysteine

2005 ◽  
Vol 58 (7) ◽  
pp. 544 ◽  
Author(s):  
Biljana V. Petrović ◽  
Živadin D. Bugarčić
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Second Order ◽  
Mechanistic Study ◽  
Stopped Flow ◽  
Substitution Reactions ◽  
Order Rate ◽  
Increase With Increase ◽  
Naclo4 Solution ◽  
Entropy Of Activation

The reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ (dien = diethylenetriamine or 1,5-diamino-3-azapentane) with l-cysteine and S-methyl-l-cysteine were studied in an aqueous 0.10 M NaClO4 solution using stopped-flow and conventional UV-vis spectrophotometry. The second-order rate constants for the reactions of [Pd(dien)H2O]2+ at pH 1.0 are k1298 = (9.11 ± 0.11) × 102 M−1 s−1 for l-cysteine, and k1298 = (33.79 ± 0.63) × 102 M−1 s−1 for S-methyl-l-cysteine. The second-order rate constants for the reactions of [Pt(dien)H2O]2+ at pH 1.0 with l-cysteine is k1298 = (1.28 ± 0.08) × 10−2 M−1 s−1 and for S-methyl-l-cysteine is k1298 = (3.87 ± 0.02) × 10−2 M−1 s−1. Activation parameters were determined for all reactions, and the negative values of entropy of activation support an associative complex formation mechanism. Substitution reactions were also studied at pH 0.5, 1.0, and 1.5. The rate constants increase with increase in pH. These results are discussed in terms of protolitic equilibrium.

Reaktionskinetische Untersuchungen zur Bildung von Carbeniumionen des Triphenylmethyl-Typs / Kinetic Investigations of the Formation of Carbenium Ions of the Triphenylmethyl Type

1975 ◽  
Vol 30 (7-8) ◽  
pp. 561-565 ◽  
Author(s):  
Matthias Walper ◽  
Hans-Dieter Brauer ◽  
Hartwig Kelm
Keyword(s):  
Acetic Acid ◽  
Acid Concentration ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Stopped Flow ◽  
Carbenium Ions ◽  
Kinetic Investigations ◽  
Flow Techniques

The rates of formation of three mono- and three dicarbenium ions of the triphenylmethyl type from the corresponding carbinols in trifluoro acetic acid - toluene mixtures were investigated using stopped flow techniques.The reaction mechanisms are discussed in view of the obtained dependencies of the rate constants on acid concentration and temperature.

Kinetic study of formation of nickel (II)-isoquinoline complex in water and nonaqueous solvents

1976 ◽  
Vol 54 (16) ◽  
pp. 2540-2547 ◽  
Author(s):  
Praphulla Kumar Chattopadhyay ◽  
Byron Kratochvil
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Activation Parameters ◽  
Nonaqueous Solvents ◽  
Stopped Flow ◽  
Multidentate Ligands ◽  
Monodentate Ligands

Rate constants and activation parameters for the formation of the monocomplex of nickel(II) with isoquinoline in water, methanol, dimethylsulfoxide, and N,N-dimethylformamide were obtained from measurements by stopped-flow spectrophotometry. The data are compared with previously reported work by other authors for substitution at nickel(II) with related monodentate and multidentate ligands. The results in all solvents except dimethylsulfoxide are consistent with an Id mechanism. In dimethylsulfoxide substitution at nickel(II) proceeds in a similar way for all monodentate ligands but whether the mechanism is Id or D cannot be ascertained.

Aromatic substitutions with carbanion nucleophiles. IV. The kinetics and mechanism of the reaction of picryl bromide with diethylmalonate anion

1977 ◽  
Vol 55 (14) ◽  
pp. 2664-2669 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Anna E. Matinopoulos-Scordou
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Activation Parameters ◽  
Solvent System ◽  
Stopped Flow ◽  
Substitution Product ◽  
Picryl Chloride ◽  
Uv Visible ◽  
The Individual ◽  
Mechanism Of The Reaction

The reaction of picryl bromide with sodium diethylmalonate has been studied in benzene–DMSO 7:1 v/v by means of stopped-flow and uv–visible spectrophotometers. A Meisenheimer-like intermediate was detected, decomposing to yield the stable violet anion of the substitution product. The rate constants of the individual steps have been measured and the activation parameters calculated. Comparison with those obtained for picryl chloride support a bimolecular substitution via the 1,1-complex. The reaction with 1,3,5-trinitrobenzene is too fast to be measured in the same solvent system. The equilibrium constant is estimated to be of the order of 104–105.

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.

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