Intramolecular general base catalyzed ester hydrolysis. The hydrolysis of 2-aminobenzoate esters

Rate constants have been obtained for the hydrolysis of the trifluoroethyl, phenyl, and p-nitrophenyl esters of 2-aminobenzoic acid at 50 degrees C in H(2)O. The pseudo-first-order rate constants, k(obsd), are pH independent from pH 8 to pH 4 (the pK(a) of the amine group conjugate acid). The 2-aminobenzoate esters hydrolyze with similar rate constants in the pH-independent reactions, and these water reactions are approximately 2-fold slower in D(2)O than in H(2)O. The most likely mechanism involves intramolecular general base catalysis by the neighboring amine group. The rate enhancements in the pH-independent reaction in comparison with the pH-independent hydrolysis of the corresponding para substituted esters or the benzoate esters are 50-100-fold. In comparison with the hydroxide ion catalyzed reaction, the enhancement in k(obsd) at pH 4 with the phenyl ester is 10(5)-fold. Intramolecular general base catalyzed reactions are assessed in respect to their relative advantages and disadvantages in enzyme catalysis. A general base catalyzed reaction can be more rapid at low pH than a nucleophilic reaction that has a marked dependence on pH and the leaving group.     

Ferrocenyl carbocations. The hydrolysis of ferrocenyl arylmethyl acetates

The hydrolysis of a series of ferrocenyl arylmethyl acetates, FcCH(OAc)(p-XC₆H₄) (Fc=ferrocenyl group; X= OCH₃, CH₃, H, Cl, Br, NO₂), has been studied in acetone-water 4:1 v/v. The logarithms of the first-order rate constant fairly correlate with σ⁺substituent constants and with E_{$\text{1}\text{2}$} chronopotentiometric potentials. However, the sensitivity of the system to the substituent effects on the aryl group, as revealed by a ? value of ?1.40, is sharply-lower than that of trityl and benzhydryl systems, as well as of heteroannularly substituted ferrocenyl derivatives. The results are interpreted as due to the high electron-releasing effect of the Fc group and to the localization of a considerable positive charge onto the iron atom in the reactions involving the formation of α-ferrocenyl carbocations.     

The hydrolysis of dibromofluoromethyltriphenylphosphonium bromide

Hydrolysis of [Ph₃$\text{P}\text{+}$PCFBr₂]Br^? afforded a high yield of dibromofluoromethane and triphenylphosphine oxide. Hydrolysis in the presence of a radioactive isotope of bromine gave evidence that the mechanism of this reaction proceeds $\text{via}$ the dibromofluoromethide ion and not $\text{via}$ a bromofluorocarbene intermediate.     

Base-catalyzed hydrolysis of 6-aminopenicillanic acid. The kinetic and thermodynamic products

In the presence of sodium hydroxide or a β-lactamase, 6-APA has been shown to hydrolyze rapidly at room temperature to penicic acid 3 , the kinetic product of the reaction. In a subsequent equilibration 3 isomerizes at C-5, by way of intermediate imine 4 , affording 5-epi-penicic acid 6 as the major hydrolysis product (～ 95% at equilibrium). The pH and temperature parameters of equilibration are discussed and HPLC, optical rotation, proton nmr and ¹³C nmr data are presented.     

The alkaline hydrolysis of flavonoid glycosides

Conclusions 1. The alkaline hydrolysis of flavonoid glycosides has been studied.2. In an alkaline medium 3-glycosides, C-glycosides, and biosides having 1, 2 bonds between the sugars are stable.3. The difference in the stabilities of the glycosides to alkalis can be used in studying flavonoid O-diglycosides, O-biosides with different positions of the bond, O,C-diglycosides, and O,C-biosides.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 5, pp. 366–369, 1969     

The alkaline hydrolysis of 4-methoxycoumarin

The aqueous alkaline hydrolysis of 4-methoxycoumarin occurs in two stages. In the first, the lactone ring is opened at a rate directly proportional to the concentration of base. In the second, the methoxy group is replaced by an unusual route that depends upon the presence of an $\text{un}$ionised phenolic hydroxy group and is therefore inversely proportional to the concentration of base. Methanolysis by methoxide ion in methanol occurs primarily at position 4 and replaces the methoxy group before the ring is opened; the difference from the aqueous hydrolysis is ascribed to solvent effects.