Intramolecular Catalysis of Hydrolytic Reactions. IV. A Comparison of Intramolecular and Intermolecular Catalysis^1,2

Abstract

The kinetics of the acetate ion-catalyzed hydrolyses of phenyl acetate and /Miitropheny 1 acetate have been determined at three temperatures. The activation parameters of these processes have been calculated. The hydrolysis of 2,4-dinitrophenyl benzoate at pH 5.5 using acetate-O18 as catalyst led to benzoic acid containing about 75% of one oxygen-18 atom of the original acetate ion catalyst. The result of this tracer experiment suggests acetylbenzoyl anhydride as intermediate in this acetate ion catalysis and suggests the existence of anhydride intermediates in other acetate ion-catalyzed hydrolyses. The possibility of acylimidazole, acid anhydride, ester and lactone intermediates in nucleophilic catalysis is discussed, both in intramolecular and intermolecular cases. A kinetic comparison between a number of corresponding cases of intermolecular and intramolecular catalysis of hydrolytic reactions indicates the powerful nature of intramolecular catalysis and further suggests that in a rigidly held enzyme-substrate complex nucleophilic and/or electrophilic catalysis is responsible for the powerful action of enzymes in hydrolytic reactions.

Entropic Contributions to Rate Accelerations in Enzymic and Intramolecular Reactions and the Chelate Effect

“…2) is about 105 M (4,10,11 (17,18), but this requires the use of liquid-phase data obtained under unusual conditions of high pressure. We believe it is both simpler and more meaningful to carry out comparisons at constant pressure, for which AH for a 2 --1 reaction in the gas phase differs ideally only by RT from that at constant volume.…”

Understanding Methyl Salicylate Hydrolysis in the Presence of Amino Acids

“…Once the amine group of Gly is substituted or partially protonated, the energy barrier of the transition state increases, making 1 hydrolysis reaction more difficult to proceed. According to the literature, the nitrogen-based group in organic media is typically a more effective nucleophile than the carboxylate group in the hydrolysis of the ester . The key finding of the current work is that the water molecule can form a stable complex with the carboxyl group of amino acid via hydrogen bonding.…”

“…According to the literature, the nitrogenbased group in organic media is typically a more effective nucleophile than the carboxylate group in the hydrolysis of the ester. 38 The key finding of the current work is that the water molecule can form a stable complex with the carboxyl group of amino acid via hydrogen bonding. Importantly, our result suggests that the water oxygen in the Gly−H 2 O complex can be a more effective nucleophile than the amine group for the ester hydrolysis of 1.…”

A possibility of influence of the degree of coiling of macromolecules in solution on the kinetics of side‐groups reactions

“…Our case is rather more complicated than that of end-groups. There are many known factors affecting this type of reaction : electrostatic,l0-'2 specific, [13][14][15] or catalytic effect of neighboring groups, [16][17][18][19] and also the effect of diffusion . 20 The present work was undertaken to determine whether the degree of coiling might be another factor influencing the kinetics of side-group reactions in macromolecules.…”