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

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 amides

1977 ◽  
Vol 55 (16) ◽  
pp. 3050-3057 ◽  
Author(s):  
Tomasz A. Modro ◽  
Keith Yates ◽  
Françoise Beaufays
Keyword(s):  
Transition State ◽  
Bond Cleavage ◽  
Protonated Form ◽  
State Activity ◽  
Alkyl Derivatives ◽  
Amide Hydrolysis ◽  
Conjugate Acid ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Nitrogen Bond

The transition-state activity coefficient [Formula: see text] approach has been applied to the acid-catalyzed hydrolysis of benzamide and its N-alkyl derivatives. For all systems (with the exception of the N-tert-butyl derivative which reacts via carbon–nitrogen bond cleavage) a uniform type of medium dependence of [Formula: see text] is observed. The reaction shows a pronounced destabilization of S≠ over the whole region of acidity studied, practically identical to that found for the AAc-2 type of ester hydrolysis. This is interpreted in terms of an AoT2 mechanism of amide hydrolysis, that is the rate-determining formation of the oxonium-type tetrahedral intermediate from the O-protonated form of substrate conjugate acid.

Oxygen exchange in methanol in acid solutions. Transition state activity coefficients

1980 ◽  
Vol 58 (4) ◽  
pp. 393-398 ◽  
Author(s):  
Robert A. McClelland
Keyword(s):  
Sulfuric Acid ◽  
Activity Coefficient ◽  
Transition State ◽  
Activity Coefficients ◽  
Oxygen Exchange ◽  
Acid Solutions ◽  
Salting Out ◽  
Carbonium Ion ◽  
State Activity ◽  
Significant Difference

Rate constants for oxygen exchange of methanol in sulfuric acid and perchloric acid solutions are reported, along with activity coefficients of methanol in sulfuric acid. Transition state activity coefficients (f≠*) for methanol exchange and tert-butanol exchange have been calculated. Values of f≠* for the latter behave very similarly to those for tert-butyl acetate hydrolysis, consistent with a carbonium ion-like transition state. Values for methanol exchange show considerably more salting-out, consistent with an oxonium ion-like transition state. A significant difference with the AAc2 hydrolyses of esters and amides is noted. For the latter the transition state is salted-out relative to its protonated precursor, whereas for methanol exchange, there is little difference between the activity coefficient of the protonated alcohol and the transition state, with the latter actually being somewhat salted-in. It is pointed out that the transition state activity coefficient approach can be rigorously applied even in the absence of protonation data.

A SURVEY OF THERMODYNAMIC PARAMETERS FOR SOLVOLYSIS IN WATER

1959 ◽  
Vol 37 (4) ◽  
pp. 803-824 ◽  
Author(s):  
R. E. Robertson ◽  
R. L. Heppolette ◽  
J. M. W. Scott
Keyword(s):  
Transition State ◽  
Activation Enthalpy ◽  
Detailed Knowledge ◽  
Standard State ◽  
Initial State ◽  
Enthalpy Of Activation ◽  
Halide Exchange ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of ◽  
Linear Correlations

A method is suggested for determining the standard state entropies [Formula: see text] of the transition state for the neutral hydrolysis of esters in water. This has required the development of methods for approximating initial state parameters where experimental data are lacking.Characteristic linear correlations between the entropy and enthalpy of activation are observed for hydrolysis in water, as well as for the bimolecular halide exchange reaction in acetone and for acid–base equilibria. Explanations are advanced to explain the observed trends.From the derived standard state entropies, a method for estimating the charge development in the transition state for the methyl and isopropyl halides is proposed. With this further detailed knowledge of the transition state in the methyl halide series, reasonable values of the activation enthalpy can be calculated from available thermochemical data.

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