Kinetics and mechanism of phosphate-catalyzed hydrolysis of benzoate esters: comparison with nucleophilic catalysis by imidazole and o-iodosobenzoate

Phosphate-catalyzed hydrolysis of 2,4-dinitrophenyl 4-X-benzoate, and 3- or 4-Y-phenyl 3,5-dinitrobenzoates, where X and Y are substituents, has been studied spectrophotometrically. The following conclusions are based on catalytic rate constants, solvent kinetic isotope effect, detection of a mixed anhydride by FTIR, and application of the Hammett equation: (i) the catalytically active species is HPO42−, (ii) the mechanism of catalysis is nucleophilic, the reaction proceeds via the irreversible formation of acyl phosphate, (iii) the formation of a tetrahedral species by attack of the HPO42− on the ester CO group is rate limiting. Comparison of these results with our previous data on hydrolysis of benzoate esters with imidazole, or o-iodosobenzoate anion showed that: (i) the catalytic efficiency observed, o-iodosobenzoate > imidazole > phosphate, is due to a combination of steric and solvation effects, and the enhancement of the nucleophilicity of the former catalyst by the α-effect, (ii) the nonlinear Bronsted-type plot between log (catalytic constant) and pKa of the leaving 4-Y-phenol indicates that the rate-limiting step for o-iodosobenzoate changes as a function of changing Y, (iii) the reaction rate-limiting steps are different for the above-mentioned nucleophiles.

[1]  J. Shorter.  Compilation and critical evaluation of structure-reactivity parameters and equations - Part I: Values of σm, and σp based on the ionization of substituted benzoic acids in water at 25 C (Technical Report) , 1994 .

[2]  T. Fife.  Kinetic and mechanistic effects of ease of carbon-nitrogen bond breaking in amide hydrolysis. The mechanisms of hydrolysis of N-acylimidazoles and N-acylbenzimidazoles , 1993 .

[3]  Qinjian Zhao,et al.  Nucleophilic and protolytic catalysis of phosphonate hydrolysis : isotope effects and activation parameters , 1993 .

[4]  A. Kanavarioti,et al.  Catalysis of hydrolysis and nucleophilic substitution at the P-N bond of phosphoimidazolide-activated nucleotides in phosphate buffers. , 1991, The Journal of organic chemistry.

[5]  Andrew Williams.  Concerted mechanisms of acyl group transfer reactions in solution , 1989 .

[6]  D. Herschlag,et al.  Phosphoryl Transfer to Anionic Oxygen Nucleophiles. Nature of the Transition State and Electrostatic Repulsion , 1989 .

[7]  E. Buncel,et al.  Solvent-independent transition-state structure for acyl-transfer reactions. A novel strategy for construction of a Broensted correlation , 1989 .

[8]  A. Luthra,et al.  Concertedness in acyl group transfer in solution: a single transition state in acetyl group transfer between phenolate ion nucleophiles , 1987 .

[9]  R. Wallace,et al.  A phosphate-catalysed acyl transfer reaction. Hydrolysis of 4-nitrophenyl acetate in phosphate buffers , 1984 .

[10]  J. D. Bene,et al.  Molecular orbital theory of the hydrogen bond. 20. Pyrrole and imidazole as proton donors and proton acceptors , 1978 .

[11]  Derek W. Smith.  Ionic hydration enthalpies , 1977 .

[12]  J. Kirsch,et al.  Acylation of chymotrypsin by active esters of nonspecific substrates. Evidence for a transient acylimidazole intermediate. , 1972, Biochemistry.

[13]  R. Brown,et al.  Contributions to the Knowledge of Forest Products. III. Identification of Phenols as 3,5-Dinitrobenzoic-Acid Esters1 , 1922 .