Alkoxyphosphonium ions. 5. Kinetics of the Michaelis–Arbuzov intermediate

1986 ◽  
Vol 64 (6) ◽  
pp. 1156-1160 ◽  
Author(s):  
Edward S. Lewis ◽  
Bridget A. McCortney
Keyword(s):  
Propylene Carbonate ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Methyl Esters ◽  
Ion Pairing ◽  
Stable Model ◽  
Trivalent Phosphorus ◽  
Conductivity Method ◽  
Rate Determining Step ◽  
Kinetics Of

Rates of formation and destruction of the alkoxyphosphonium ion, the intermediate in the Michaelis–Arbuzov reactions of some methyl esters of trivalent phosphorus acids with methyl iodide, are followed by a conductivity method in the solvent propylene carbonate. Specific conductances of the unstable intermediates are well estimated through stable model salts. Rate constants for both the alkylation of the reagent and the dealkylation of the intermediate are obtained. The conductivity time curves are simulated by adjusting rate constants for two sequential second order reactions, assuming no ion pairing at the concentrations used. In these measurements of the intermediate only, there is no rate-determining step; for the overall reaction the first step is in most cases rate-determining.

The retroaldol reaction of 3-methyl-2-butenal

1983 ◽  
Vol 61 (1) ◽  
pp. 171-178 ◽  
Author(s):  
J. Peter Guthrie ◽  
Brian A. Dawson
Keyword(s):  
Sodium Hydroxide ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Aqueous Sodium Hydroxide ◽  
Initial Increase ◽  
Aqueous Sodium ◽  
Rate Determining Step ◽  
Kinetics Of

In aqueous sodium hydroxide solutions at 25 °C, 3-methyl-2-butenal, 1c, undergoes retroaldol cleavage to acetone and acetaldehyde. The kinetics of the retroaldol reaction were followed spectrophotometrically at 242 nm and showed simple first order behavior. When 3-methyl-3-hydroxybutanal, 2c, was added to aqueous sodium hydroxide solutions at 25 °C, there was an initial increase in absorbance at 242 nm, attributed to formation of 1c, followed by a 20-fold slower decrease; the rate of the slow decrease matches the rate of disappearance of 1c under the same conditions. Analysis of the kinetics allows determination of the three rate constants needed to describe the system: khyd = 0.00342; kdehyd = 0.00832; kretro = 0.0564; all M−1 s−1. The equilibrium constant for enone hydration is 0.41. Rate constants for the analogous reactions for acrolein and crotonaldehyde could be obtained from the literature. There is a reasonable rate–equilibrium correlation for the retroaldol step. For the enone hydration step, rate and equilibrium constants respond differently to replacement of hydrogen by methyl. It is proposed that this results from release of strain after the rate-determining step by rotation about a single bond; this decrease in strain is reflected in the equilibrium constant but not in the rate constant.

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.

Kinetics of Methylation of Methyl 5-Deoxy-α/β-D-xylofuranosides

2004 ◽  
Vol 69 (10) ◽  
pp. 1877-1888
Author(s):  
Mária Oščendová ◽  
Jitka Moravcová
Keyword(s):  
Sodium Hydroxide ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effect ◽  
Order Reaction ◽  
Half Time ◽  
First Order ◽  
Consecutive Reactions ◽  
Kinetics Of

The kinetics of methylation of methyl 5-deoxy-α-D-xylofuranoside (1), methyl 5-deoxy-β-D-xylofuranoside (2) and their partly methylated derivatives with methyl iodide in the presence of sodium hydroxide in acetonitrile was studied. The reaction rate was independent of the base concentration during the first half-time only and the methylation proceeded as a first-order reaction. The rate constants of all side and consecutive reactions were calculated and the influence of both polar and steric effect is discussed. The methylation of 1 was highly regioselective giving almost exclusively 5-deoxy-2-O-methyl-α-D-xylofuranoside.

Detailed kinetics of tetrafluoroethene ozonolysis

2018 ◽  
Vol 20 (44) ◽  
pp. 28059-28067 ◽  
Author(s):  
Tam V.-T. Mai ◽  
Minh v. Duong ◽  
Hieu T. Nguyen ◽  
Lam K. Huynh
Keyword(s):  
Experimental Data ◽  
Reaction Mechanism ◽  
Kinetic Analysis ◽  
Rate Constants ◽  
Rate Model ◽  
Rate Determining Step ◽  
Calculated Rate ◽  
Detailed Kinetics ◽  
Kinetics Of

The reaction mechanism was explored at the CCSD(T)/CBS//B3LYP/aug-cc-pVTZ level. Detailed kinetic analysis was firstly carried out using an ME/RRKM rate model with the inclusion of anharmonic and tunneling treatments. 1,3-Cycloaddition is found to be the rate-determining step. Calculated rate constants confirm the latest experimental data.

Effect of pH on the reaction of 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole with 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione

1970 ◽  
Vol 48 (19) ◽  
pp. 3104-3107 ◽  
Author(s):  
James Leslie
Keyword(s):  
Rate Constants ◽  
Ionic Species ◽  
Second Order ◽  
Hydrogen Ion ◽  
Effect Of Ph ◽  
Order Rate ◽  
Rate Determining Step ◽  
Ion Activity ◽  
Kinetics Of ◽  
Linear Manner

The kinetics of the oxidation of 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione with 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole (1) have been examined at pH 4–5.6. The reaction is second-order, which can be explained by a rate-determining step involving the reaction of one molecule of the thiol with one molecule of 1. The second-order rate constants vary in a linear manner with the reciprocal of the hydrogen ion activity. The ionic species involved in the reaction are discussed.

Kinetics and mechanism of dehydrochlorination of N-aryl-C-ethoxycarbonylformohydrazidoyl chlorides

1986 ◽  
Vol 64 (5) ◽  
pp. 871-875 ◽  
Author(s):  
Ahmad S. Shawali ◽  
Hassan A. Albar
Keyword(s):  
Rate Constants ◽  
Water Solution ◽  
Chloride Ion ◽  
Order Conditions ◽  
Rate Law ◽  
First Order ◽  
Rate Determining Step ◽  
Pseudo First Order ◽  
Reaction Constants ◽  
Kinetics Of

The kinetics of triethylamine (TEA) catalyzed deydrochlorination of a series of N-aryl-C-ethoxycarbonylformohydrazidoyl chlorides 1a–m have been studied under pseudo-first-order conditions in 4:1 (v/v) dioxane–water solution at 30 °C. For all compounds studied, the kinetics followed the rate law: kobs = k2 (TEA). The values of the overall second-order rate constants for the studied compounds were correlated by the equation: log k2 = 0.533σ−-0.218. The results are compatible with a mechanism involving a fast reversible deprotonation step leading to the anion of 1, followed by rate-determining step involving the loss of the chloride ion from the anion. The reaction constants of these two steps were estimated to be 0.845 and −0.312, respectively.

Reaction kinetics of hydrogen addition reactions to methyl butenoate

2020 ◽  
Vol 22 (9) ◽  
pp. 5286-5292
Author(s):  
Yage Gao ◽  
Xiaoyu Li ◽  
Xiaoqing You
Keyword(s):  
Reaction Kinetics ◽  
Chemical Kinetics ◽  
Rate Constants ◽  
Methyl Esters ◽  
Hydrogen Abstraction ◽  
Addition Reactions ◽  
Hydrogen Addition ◽  
Kinetics Of

We study the chemical kinetics of hydrogen addition reactions of unsaturated methyl esters, methyl 2-butenoate and methyl 3-butenoate, and compare the rate constants with those of hydrogen abstraction reactions by H atom.

Kinetics and mechanism of oxidation of nickel(II) tetraazamacrocycles by the peroxydisulphate anion in aqueous and binary aqueous mixtures

1992 ◽  
Vol 70 (11) ◽  
pp. 2785-2791 ◽  
Author(s):  
Robert I. Haines ◽  
Sandra J. Northcott
Keyword(s):  
Rate Constants ◽  
Metal Ion ◽  
Ion Pairing ◽  
Ion Pair ◽  
Aqueous Mixtures ◽  
Kinetics Of Oxidation ◽  
Steric Factors ◽  
Temperature Dependences ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

The kinetics of oxidation of several nickel(II) tetraazamacrocycles by the peroxydisulphate anion have been studied in water and in binary aqueous mixtures. The reactions proceed via an ion-pairing pre-equilibrium, followed by metal ion-assisted peroxy-bond fissure within the ion-pair solvent shell. The derived rate law is[Formula: see text]Ion-pairing constants have been determined and have been found to be little influenced by steric factors, but do depend on solvent composition. Rate constants have been extracted using the rate expression and activation energies have been estimated from temperature dependences.

Ion Pairing and the Reaction of Alkali Metal Ferrocyanides and Persulfates

1971 ◽  
Vol 49 (18) ◽  
pp. 2943-2947 ◽  
Author(s):  
R. W. Chlebek ◽  
M.W. Lister
Keyword(s):  
Alkali Metal ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Ion Pairs ◽  
Activation Parameters ◽  
Ion Pairing ◽  
Similar Rate ◽  
Thermodynamic Quantities ◽  
Kinetics Of

Osmometric measurements have been made on the alkali metal persulfates, and these are interpreted in terms of formation of ion pairs, MS2O8−, by means of the method of Masterton and Berka (5). Equilibrium constants, and the derived thermodynamic quantities are deduced for the reactions [Formula: see text]. These results are applied to the interpretation of the kinetics of the reactions[Formula: see text]With M = K+, Rb+, and Cs+, the reacting species are MFe(CN)63− + MS2O8−, with very similar rate constants; with M = Li+, Na+ the species are MFe(CN)63− + S2O82−; and for lithium the reaction of Fe(CN)64− + S2O82− is also important. Rate constants and activation parameters are deduced.

The kinetics of the photo-oxidation of benzaldehyde

1953 ◽  
Vol 218 (1133) ◽  
pp. 175-189 ◽  
Keyword(s):  
Rate Constants ◽  
Peroxy Radical ◽  
Photochemical Oxidation ◽  
Square Root ◽  
Peroxy Radicals ◽  
Photo Oxidation ◽  
Rate Determining Step ◽  
Perbenzoic Acid ◽  
Kinetics Of ◽  
Overall Kinetics

The direct photochemical oxidation of liquid benzaldehyde in n -decane solution has been investigated at temperatures from 5 to 20° C, the primary product being perbenzoic acid. The overall kinetics of the reaction are simple, the rate being proportional to the first power of the concentration of the aldehyde and to the square root of the intensity of the absorbed light. The rate is independent of oxygen pressure. These kinetics indicate that the dehydrogenation of the aldehyde by the peroxy radical is the rate-determining step in propagation. The termination step involves the interaction of two peroxy radicals. By means of the retardation and sector techniques the rate of initiation of the oxidation and the values of the rate constants have been determined.

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