EN
The second-order rate constants k for the alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, in aqueous 50.9% acetonitrile have been measured spectrophotometrically at 25°C. The log k values for meta and para derivatives correlated well with the Hammett σm,p substituent constants. The log k values for ortho-substituted phenyl benzoates showed good correlations with the Charton equation, containing the inductive, σI, resonance, σ○
R, and steric, E
s
B, and Charton υ substituent constants. For ortho derivatives the predicted (log k
X)calc values were calculated with equation (log k
ortho)calc = (log k
H
AN)exp + 0.059 + 2.19σI + 0.304σ○
R + 2.79E
s
B − 0.0164ΔEσI - 0.0854ΔEσ○
R, where DE is the solvent electrophilicity, ΔE = E
AN - E
H20 = −5.84 for aqueous 50.9% acetonitrile. The predicted (log k
X)calc values for phenyl ortho-, meta- and para-substituted benzoates in aqueous 50.9% acetonitrile at 25°C precisely coincided with the experimental log k values determined in the present work.The substituent effects from the benzoyl moiety and aryl moiety were compared by correlating the log k values for the alkaline hydrolysis of phenyl esters of substituted benzoic acids, X-C6H4CO2C6H5, in various media with the corresponding log k values for substituted phenyl benzoates, C6H5CO2C6H4-X.