Kinetic medium effects. IV. Transition state activity coefficients in mixed solvents

1972 ◽  
Vol 25 (4) ◽  
pp. 777 ◽  
Author(s):  
PT McTigue ◽  
AR Watkins
Keyword(s):  
Transition State ◽  
Activity Coefficients ◽  
Mixed Solvents ◽  
State Theory ◽  
Medium Effects ◽  
State Activity ◽  
Medium Activity ◽  
Solvent Systems ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of acid hydrolysis of a number of aliphatic acetals have been studied in dimethyl sulphoxide-water and dioxan-water mixtures. Where possible, experimentally measured medium activity coefficients for the acetals in the solvent systems have been used in order to calculate the transition state activity coefficients as a function of solvent composition. These activity coefficients are compared with those calculated for the transition states of other hydrolytic reactions, and with the known activity coefficients of some stable ions. The results show no features inconsistent with the assumptions of transition state theory.

Kinetics of the hydrolysis of acetic anhydride and the reaction of 4-nitrophenyl acetate with imidazole in aqueous-organic mixed solvents

1974 ◽  
Vol 27 (7) ◽  
pp. 1423 ◽  
Author(s):  
DG Oakenfull
Keyword(s):  
Acetic Anhydride ◽  
Organic Solvent ◽  
Transition State ◽  
Activity Coefficients ◽  
Butyl Alcohol ◽  
Dimethyl Sulphoxide ◽  
Kinetics Of Hydrolysis ◽  
State Activity ◽  
Kinetics Of ◽  
Hydrolysis Of

With the general aim of elucidating the role of water structure in the kinetics of hydrolysis, a comparative study has been made of the kinetics of the hydrolysis of acetic anhydride and the reaction of 4-nitrophenyl acetate with imidazole in mixtures of water with ethanol, t-butyl alcohol, dimethyl sulphoxide and dioxan. Both rate constants were always reduced by the addition of organic solvent. Transition state activity coefficients were measured for both reactions in dimethyl sulphoxide-water mixtures and compared with the activity coefficient of phenylalanine (a model zwitterionic transition state). Activation parameters were measured for the hydrolysis of aceticanhydride in t-butyl alcohol-water and dimethyl sulphoxide-water mixtures. Semilogarithmic plots of rate constant against Winstein's Y-value were non-linear for some of the solvents and this fact, coupled with the effect of dimethyl sulphoxide on the transition state activity coefficients, leads to the conclusion that specific interactions of the solvent with the reactants and with the transition state could be of major importance in controlling the reaction rate.There was no obvious relationship between the effect of an organic solvent on the kinetics of hydrolysis of acetic anhydride and its effect on the structure of water.

Transition state activity coefficients in the acid-catalyzed hydrolysis of esters

1975 ◽  
Vol 97 (18) ◽  
pp. 5223-5231 ◽  
Author(s):  
Robert A. McClelland ◽  
Tomasz A. Modro ◽  
Malcolm F. Goldman ◽  
Keith Yates
Keyword(s):  
Transition State ◽  
Activity Coefficients ◽  
State Activity ◽  
Acid Catalyzed ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Kinetics of the hydrolysis of acetic anhydride in concentrated salt solutions

1971 ◽  
Vol 24 (12) ◽  
pp. 2547 ◽  
Author(s):  
DG Oakenfull
Keyword(s):  
Free Energy ◽  
Acetic Anhydride ◽  
Transition State ◽  
Activity Coefficients ◽  
Rate Constants ◽  
Water Structure ◽  
Salt Solutions ◽  
Measured Activity ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of the hydrolysis of acetic anhydride have been investigated in concentrated salt solutions at 20�. Sine salts were used in concentrations of up to 5 mol 1-1; all inhibited the reaction. ��� The salt effect was resolved into its component effects on the reactants and the transition state by use of the Bronsted-Bjerrum equation to calculate transition state activity coefficients from rate constants and measured activity coefficients of acetic anhydride. The effect of a salt on the free energy of the reactants was always significant and in some cases it was the major component of the effect of the salt on the free energy of activation. The enthalpy and entropy of transfer from water to 1 mol l-1 sodium chloride, for both acetic anhydride and the transition state, show the enthalpy-entropy compensation effect which is typical of aqueous solutions. ��� These salt effects are considered to be part of the general phenomenon of the effect of salts on the activity coefficients of non-electrolytes. The inhibition is not caused by formation of a complex between salt and acetic anhydride. Rate constants could not be correlated with dielectric constant and ionic strength, using Gold's equation, and changes in water structure which occur in these salt solutions were shown to have no direct effect on the reaction rate.

On the Calculation of Transition State Activity Coefficient and Solvent Effects on Chemical Reactions

1998 ◽  
Vol 63 (12) ◽  
pp. 1969-1976 ◽  
Author(s):  
Alvaro Domínguez ◽  
Rafael Jimenez ◽  
Pilar López-Cornejo ◽  
Pilar Pérez ◽  
Francisco Sánchez
Keyword(s):  
Activity Coefficient ◽  
Transition State ◽  
Chemical Reactions ◽  
Solvent Effects ◽  
Transition State Theory ◽  
Reaction Medium ◽  
State Theory ◽  
Precursor Complex ◽  
State Activity ◽  
Classical Transition

Solvent effects, when the classical transition state theory (TST) holds, can be interpreted following the Brønsted equation. However, when calculating the activity coefficient of the transition state, γ# it is important to take into account that this coefficient is different from that of the precursor complex, γPC. The activity coefficient of the latter is, in fact, that calculated in classical treatments of salt and solvent effects. In this paper it is shown how the quotients γ#/γPC change when the reaction medium changes. Therefore, the conclusions taken on the basis of classical treatments may be erroneous.

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