First reaction steps and intermediates of the oxidation of ascorbic acid by dioxygen. Catalysis by cobalt(II) tetrasulphophthalocyanine

1982 ◽  
Vol 47 (3) ◽  
pp. 755-765 ◽  
Author(s):  
Dana M. Wagnerová ◽  
Jürgen Blanck ◽  
Josef Vepřek-Šiška
Keyword(s):  
Ascorbic Acid ◽  
Rate Constants ◽  
Reactive Intermediates ◽  
Stopped Flow ◽  
Absorption Bands ◽  
Flow Method ◽  
The Individual

The oxidation of ascorbic acid by dioxygen catalyzed by cobalt(II) tetrasulphophthalocyanine (CoTSP) has been studied by the stopped-flow method. Two reactive intermediates, [O2.CoTSP. ascorbic acid] and [O2.CoTSP], characterized by separate absorption bands at 570 nm and 634 nm, respectively, have been proved to form in the reaction. The individual steps of the reaction have been elucidated, and their rate constants have been determined or estimated.

The kinetics of partial processes in the oxidation of ascorbic acid catalyzed by vanadyl tetrasulphophthalocyanine

1982 ◽  
Vol 47 (3) ◽  
pp. 744-754 ◽  
Author(s):  
Dana M. Wagnerová ◽  
Jaroslav Votruba ◽  
Jürgen Blanck ◽  
Josef Vepřek-Šiška
Keyword(s):  
Experimental Data ◽  
Ascorbic Acid ◽  
Reaction Mechanism ◽  
Rate Constants ◽  
Stopped Flow ◽  
Adaptive Identification ◽  
Flow Method ◽  
Acid Catalyzed ◽  
Kinetics Of

The rapid partial reactions of the oxidation of ascorbic acid by dioxygen with vanadyl tetrasulphophthalocyanine as a catalyst were studied by the stopped-flow method. The experimental data were treated on a computer and compared with the kinetic implications resulting from the proposed mechanism. Application of the adaptive identification method led to quantitative solution of the mechanism, i.e. determination of the values of all the isolated rate constants of the reaction mechanism.

Mechanism of bromination of a quaternary pyrimidinium cation. Change of rate determining step with acidity

1978 ◽  
Vol 56 (23) ◽  
pp. 2970-2976 ◽  
Author(s):  
Oswald S. Tee ◽  
David C. Thackray ◽  
Charles G. Berks
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Aqueous Media ◽  
Stopped Flow ◽  
Flow Method ◽  
High Acidity ◽  
Rate Determining Step ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of bromination of the 1,2-dihydro-1,3-dimethyl-2-oxopyrimidinium cation (Q+) in aqueous media (pH 0–5) have been studied using the stopped-flow method. At the higher acidities (pH < 2) the results are consistent with rate determining attack by bromine upon the pseudobase (QOH), whereas at low acidities (pH > 4) it appears that pseudobase formation is rate determining. The change occurs because at high acidity the reversal of the pseudobase QOH to the cation is fast relative to bromine attack, whereas at low acidity the converse is true. Results obtained at intermediate acidities (pH 2–4) are consistent with this interpretation.A separate kinetic study of pseudobase formation (and decomposition) yielded rate constants in good agreement with those derived from the bromination study.

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.

scholarly journals Kinetics of the Reversible Transformation of 2,3-Dioxogulonic Acid into its Enol as a Function of the pH of the Medium

1978 ◽  
Vol 33 (10) ◽  
pp. 1184-1189
Author(s):  
J. Zuluaga ◽  
P. Martínez
Keyword(s):  
Kinetic Study ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Disodium Salt ◽  
Stopped Flow ◽  
Free Energies ◽  
Reversible Transformation ◽  
Flow Method ◽  
Kinetic Coefficients ◽  
Kinetics Of

Abstract 2,3-dioxogulonic acid and the disodium salt of its enol were synthesised, isolated and identified both chemically and spectroscopically. A kinetic study was carried out on its equilibrium by means of the “stopped flow” method for rapid processes, and the rate constants for the forward and backward reaction were determined as a function of the pH of the medium. The kinetic coefficients involved, equilibrium constant and Gibbs free energies were also determined.

scholarly journals Competitive kinetics versus stopped flow method for determining the degradation rate constants of steroids by ozonation

SpringerPlus ◽  
2016 ◽  
Vol 5 (1) ◽  
Author(s):  
Alberto López-López ◽  
Valentín Flores-Payán ◽  
Elizabeth León-Becerril ◽  
Leonel Hernández-Mena ◽  
Ramiro Vallejo-Rodríguez
Keyword(s):  
Rate Constants ◽  
Degradation Rate ◽  
Stopped Flow ◽  
Flow Method ◽  
Competitive Kinetics

Ionization of 9-cyanofluorene in Me2SO–water mixtures. The role of solvent reorientation in proton tranfers

1986 ◽  
Vol 64 (6) ◽  
pp. 1273-1275
Author(s):  
Claude F. Bernasconi ◽  
François Terrier
Keyword(s):  
Rate Constants ◽  
Intrinsic Rate ◽  
Log P ◽  
Stopped Flow ◽  
Flow Method ◽  
Methoxide Ion ◽  
Carbon Acid ◽  
Role Of Solvent ◽  
Primary Aliphatic Amines

Rate constants of the reversible deprotonation of 9-cyanofluorene by primary aliphatic amines were measured in 10%, 50%, and 90% aqueous Me2SO (v/v) by the stopped-flow method. Intrinsic rate constants defined as k0 = k1B/q = k−1BH+/p at ΔpK + log (p/q) = 0 were obtained from Brønsted plots. The values for log k0 are 3.60 ± 0.15 in 10%, 3.81 ± 0.10 in 50%, and 3.61 ± 0.05 in 90% Me2SO. The constancy of k0 with increasing Me2SO content of the solvent contrasts with results obtained by Ritchie (C. D. Ritchie, J. Am. Chem. Soc. 91, 6749 (1969)) who found that k0 for the ionization of 9-carbomethoxyfluorene by carboxylate ions in Me2SO is much higher than for the ionization of the same carbon acid by methoxide ion in methanol. Our findings suggest that it is mainly early desolvation of the oxyanions in the hydroxylic solvent which accounts for Ritchie's results.

How to predict changes in solvolysis mechanisms

2009 ◽  
Vol 81 (4) ◽  
pp. 667-683 ◽  
Author(s):  
Herbert Mayr ◽  
Armin R. Ofial
Keyword(s):  
Rate Constants ◽  
Laser Flash ◽  
Correlation Equation ◽  
Stopped Flow ◽  
Absolute Rate ◽  
Subsequent Reaction ◽  
Leaving Group ◽  
Common Ion ◽  
Leaving Groups ◽  
The Individual

Stopped-flow and laser flash techniques have been employed to investigate the individual steps of the solvolysis reactions of benzhydryl (diarylmethyl) halides and carboxylates. In this way, absolute rate constants for the ionization (k1), recombination of the carbocation with the leaving group (k-1), and subsequent reaction with the solvent (kSolvOH) have been determined. As the stabilization of the carbocations increases, the mechanism changes from (a) SN1 reactions with irreversible ionization through (b) SN1 reactions with common-ion return and (c) SN2C+ reactions, where the intermediate carbocations accumulate, to (d) the formation of persistent carbocations which do not undergo subsequent reactions under the selected solvolysis conditions. The correlation equation log k = s(N + E), where the carbocations are characterized by the electrophilicity parameter E, and leaving groups and solvents are characterized by the nucleophile-specific parameters s and N can be employed to predict the changes of mechanism.

scholarly journals A stopped-flow method for the determination of ascorbic acid in orange juice containing triose reductone.

1979 ◽  
Vol 43 (10) ◽  
pp. 2191-2192 ◽  
Author(s):  
Hitsohi OBATA ◽  
Tai TOKUYAMA ◽  
Yasunori NITTA ◽  
Masanosuke TAKAGI ◽  
Keitarou HIROMI
Keyword(s):  
Ascorbic Acid ◽  
Orange Juice ◽  
Stopped Flow ◽  
Flow Method

scholarly journals A Stopped-Flow Method for the Determination of Ascorbic Acid in Orange Juice Containing Triose Reductone

1979 ◽  
Vol 43 (10) ◽  
pp. 2191-2192
Author(s):  
Hitsohi Obata ◽  
Tai Tokuyama ◽  
Yasunori Nitta ◽  
Masanosuke Takagi ◽  
Keitarou Hiromi
Keyword(s):  
Ascorbic Acid ◽  
Orange Juice ◽  
Stopped Flow ◽  
Flow Method

Kinetics of esterification of monoisopropylphenols with phosphoryl trichloride

1989 ◽  
Vol 54 (5) ◽  
pp. 1311-1317
Author(s):  
Miroslav Magura ◽  
Ján Vojtko ◽  
Ján Ilavský
Keyword(s):  
Liquid Phase ◽  
Rate Constants ◽  
Reaction Rates ◽  
Activation Energies ◽  
The Individual ◽  
Kinetics Of

The kinetics of liquid-phase isothermal esterification of POCl3 with 2-isopropylphenol and 4-isopropylphenol have been studied within the temperature intervals of 110 to 130 and 90 to 110 °C, respectively. The rate constants and activation energies of the individual steps of this three-step reaction have been calculated from the values measured. The reaction rates of the two isomers markedly differ: at 110 °C 4-isopropylphenol reacts faster by the factors of about 7 and 20 for k1 and k3, respectively. This finding can be utilized in preparation of mixed triaryl phosphates, since the alkylation mixture after reaction of phenol with propene contains an excess of 2-isopropylphenol over 4-isopropylphenol.

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