KINETICS OF THE CATALYZED HYDROLYSIS OF p-NITROPHENYL ACETATE

Abstract

Catalytic constants have been determined for the hydrolysis a t 20 OC of p-nitrophenyl acetate in 9.56% (w/w) dioxane-water mixtures; catalysts used were hydroxide ions, imidazole and 2-methylimidazole, various substituted pyridines, serine, histidine and histidylhistidine. In the case of hydroxide ion catalysis, the rate coilstant falls off a t high catalyst concentrations, and this is attributed to the establishment of a n equilibrium involving the anion of the substrate. The results with the various catalysts indicate that there is no simplecorrelation between catalytic efficiency and pK or nucleophilicity. In the imidazole series there is evidence of steric hindrance when a group is present in a position next t o the functional group. There is a n indication of bifunctional catalysis in the hydrolysis by 2-(8-hydroxyethy1)pyridine and 4-(r-hydroxypropyl)pyridine, both of which are much more effective than pyridine.

Unraveling the Mechanisms of Carboxyl Ester Bond Hydrolysis Catalyzed by a Vanadate Anion

“…The base-catalyzed hydrolysis of the majority of common esters occurs through nucleophilic attack of the hydroxide ion at the carbonyl carbon atom. A variety of experimental investigations have been reported about the ester hydrolysis catalyzed by alkaline solutions − and by hydroxide functions activated by an adjacent Lewis acid, mostly the Zn II ion. − However, most of the theoretical work is limited to ester hydrolysis catalyzed by alkaline solutions. − Common organic molecules such as imidazole and 2-methylimidazole, various substituted pyridines, and several enzymes (e.g., chymotrypsin, acetylchinolinesteraese, dehydrogenase, and ribonuclease) have been exploited as catalysts. ,,− A variety of metal complexes including cobalt, zinc, copper, and many lanthanides have been found to be effective at promoting hydrolysis . Previous studies have suggested that metal complexes are effective catalysts because of the possibility of Lewis acid activation, formation of an intramolecular nucleophile at physiological pH, or stabilization of the leaving group. , Several oxyanions, including MoO 4 2– , WO 4 2– , and CrO 4 2– , were also tested for their ability to cleave carboxylic acid esters; however, only CrO 4 2– and MoO 4 2– were shown to be hydrolytically active. − …”

Thiohydantoins. XI Kinetic Studies of the Alkaline Hydrolysis of 1-Acyl-2-thiohydantoins

“…1). This facility of hydrolysis is shared by other amides (5-7) and esters (8) having electron-attracting groups attached to the nitrogen or oxygen atom which separates from the acyl group in hydrolysis; there is a very rough correlation between the rate of the reaction and the stability of the anion A-derived by ionization of the amino or alcohol moiety HA formed in the hydrolysis (as measured by the pKHA of HA (9-1 1 )).…”