Alkaline hydrolysis of glycol esters - A newly suggested criterion in the assessment of anchimeric assistance

1974 ◽  
Vol 27 (11) ◽  
pp. 2325 ◽  
Author(s):  
M Balakrishnan ◽  
Rao G Venkoba ◽  
N Venkatasubramanian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Alkaline Hydrolysis ◽  
Triethylene Glycol ◽  
Binary Solvent ◽  
Solvent Mixtures ◽  
Acetone Water ◽  
Anchimeric Assistance ◽  
Hydrolysis Of ◽  
Suggested Criterion

Solvent effects vis a vis structural effects on the alkaline hydrolysis of various di-and mono-benzoates of glycols have been studied in binary solvent mixtures of dimethyl sulphoxide-water, ethanol-water and acetone-water. It is observed that the higher the stabilization of the transition state by the neighbouring group, the greater is the susceptibility of the reaction to dipolar aprotic solvent acceleration[i.e. k(Me2SO)/k(EtOH) value]. The possibility of employing such solvent effects to evaluate the extent of anchimeric assistance in ester hydrolysis where the neighbouring group can stabilize the transition state is examined. The studies have been extended to triethylene glycol derivatives and it is suggested that dipolar aprotic-protic solvent effects could be used as a kinetic probe for the conformation of the molecule.

Kinetic Study of the Acid Hydrolysis of Ethyl Hydrogen Succinate in Binary Solvent Mixtures

1978 ◽  
Vol 33 (12) ◽  
pp. 1479-1483 ◽  
Author(s):  
Fayez Y. Khalil ◽  
M. T. Hanna
Keyword(s):  
Organic Solvent ◽  
Free Water ◽  
Solvent Composition ◽  
Initial Increase ◽  
Binary Solvent ◽  
Specific Rate ◽  
Water Medium ◽  
Solvent Mixtures ◽  
Acetone Water ◽  
Hydrolysis Of

Abstract The specific rate constants for the acid-catalysed hydrolysis of ethyl hydrogen succinate in water and in a series of acetone-water and dioxane-water mixtures were determined at 30-45 °C. The solvent composition covered the range 0-90% by weight of the organic solvent. The rate was found to decrease to a minimum at about 80% of the organic solvent then to increase again with successive addition of the latter. In dioxane-water medium a slight initial increase in rate on the first addition of dioxane to water was observed and attributed to an increase in the number of "free" water molecules. The activation energy showed only slight dependence on solvent composition. The radius of the activated complex was calculated in the two media. The thermodynamic parameters were evaluated and discussed in terms of solvent composition. The reaction proved to be essentially an ion-dipole rather than an ion-ion interaction. A comparative discussion of the specific solvent effects of the two solvent systems under consideration is presented, based on the respective bond energies as given by the heats of mixing of the solvent components.

Effect of Medium on Reactivity for Alkaline Hydrolysis of p-Nitrophenyl Acetate and S-p-Nitrophenyl Thioacetate in DMSO-H2O Mixtures of Varying Compositions: Ground State and Transition State Contributions

2021 ◽  
Author(s):  
Ik-Hwan Um ◽  
Seungjae Kim
Keyword(s):  
Transition State ◽  
Alkaline Hydrolysis ◽  
Ground State ◽  
Rate Constants ◽  
Kinetic Data ◽  
Reaction Medium ◽  
Stepwise Mechanism ◽  
Rate Determining Step ◽  
Leaving Group ◽  
Hydrolysis Of

Second-order rate constants (kN) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH‒ have been measured spectrophotometrically in DMSO-H2O mixtures of varying compositions at 25.0 ± 0.1 oC. The kN value increases from 11.6 to 32,800 M‒1s‒1 for the reactions of 1 and from 5.90 to 190,000 M‒1s‒1 for those of 2 as the reaction medium changes from H2O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H2O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state (TS), i.e., the reactions of 1 and 2 with OH‒ proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step (RDS). Addition of DMSO to H2O would destabilize OH‒ through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH‒ in the ground state (GS) is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the GS and TS contributions through combination of the kinetic data with the transfer enthalpies (ΔΔHtr) from H2O to DMSO-H2O mixtures for OH‒ ion.

Characterization of Alcohol Solvents by the Empirical Polarity Parameters AN, Z, and ET(30)

1982 ◽  
Vol 37 (6) ◽  
pp. 684-687 ◽  
Author(s):  
Horst Elias ◽  
Michael Dreher ◽  
Sabine Neitzel ◽  
Harald Volz
Keyword(s):  
Benzyl Alcohol ◽  
Solvent Effects ◽  
Binary Solvent ◽  
Solvent Mixtures ◽  
Acceptor Number ◽  
Binary Solvent Mixtures ◽  
Alcohol Solvents ◽  
Polarity Parameters

AbstractThe acceptor number AN and the polarity parameters Z and ET(30) were determined for a series of alcohols applied as media in the study of kinetic solvent effects. The alcohols thus characterized are methanol, ethanol, 1-propanol, 1-butanol, 2-butanol, 2-methyl-2-butanol, 3-pentanol, 2-chloroethanol, 2-methoxyethanol, 2-phenylethanol, 2-cyanoethanol, benzyl alcohol, 3-ethyl-3-pentanol, 2,4-dimethyl-3-pentanol, and 3-ethyl-2,4-dimetliyl-3-pentanol. In addition, AN was determined for 1,2-dichloroethane and Z for the binary solvent mixtures methanol/2-methyl-2-butanol, ethanol/2,2,2-trifluoroethanol. and methanol/pyridine. The data obtained are correlated and the parameters AN, Z, and ET(30) are critically compared.

Sign in / Sign up

Export Citation Format

Share Document