PH—Independent hydrolysis of 4-nitrophenyl

Solvolysis rates of isopropenyl chloroformate, CH2=C(Me)0C(0)Cl, were shown to be very similar to those for 4-nitrobenzoyl chloride in mechanism and reactivity.29 Stepwise mechanisms were observed in the aminolysis of aryl chloroformates by a series of substituted quinuclidines - which were more reactive than isobasic secondary alicyclic amines.30 The pH-independent hydrolysis of 4-nitrophenyl chloroformate in MeCN-H20 mixtures proceeded via a cyclic transition state containing the ester and two water molecules.15 Solvolyses of 2-furancarbonyl chloride in most... 

The values of ko,j for pH-independent hydrolysis of 4-nitrophenyl chlorofor-mate were lower in the nonionic micelles of polyoxyethylene (9) nonylphenyl ether compared to that in the aqueous pseudophase. " These results were explained in terms of lower microscopic polarity at the reaction site in the micelle. An H NMR study of the solubilization revealed that the average solubilization site of solubilizate (4-nitrophenyl chloroacetate) did not depend on the charge of the micelle or the length of the surfactant hydrophobic tail. " ... 

Possidonio, S., Sivierro, F., El Seoud, O.A. Kinetics of the pH-independent hydrolysis of 4-nitrophenyl chloroformate in aqueous micellar solutions effects of the charge and structure of the surfactant. J. Phys. Org. Chem. 1999,12(A), 325-332. 

The Bronsted coefficient p for imidazole catalysis of p-nitrophenyl acetate hydrolysis is 0.8 [29], and the second-order rate constants of all His residues can therefore be related to that of 4-methylimidazole to determine whether there are effects on reactivity beyond those of differential nudeophilicity and levels of protonation. The reactivity of His residues in the pH independent region may be estimated from rate constants, pH and values. The second-order rate constant of the 4-methylimidazole catalyzed hydrolysis of mono-p-nitrophenyl fumarate at pH 5.85 and 290 K is 1.02 x 10 s. From this value and the pfC of 7.9, the second-... 

Fife et al. have reported intramolecular GB-assisted ester hydrolysis. The pseudo-first-order rate constants (k bj.) are pH-independent from pH 8 to pH 4. The triflnoroethyl, phenyl, and p-nitrophenyl esters of 2-aminobenzoic acid hydrolyze with similar rate constants in the pH-independent reactions, and the rates of these water reactions are twofold slower in D2O than in HjO. The most likely mechanism involves the intramolecular GB assistance by the neighboring amino group. The rate enhanc ents in the pH-independent reaction in comparison with the pH-indepen-dent hydrolysis of the corresponding para-substituted esters are 50- to 100-fold. 

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