Substituent effects on the base-catalysed hydrolysis of phenyl esters of ortho-substituted benzoic acids

Fourteen model phenyl esters of 2-substituted benzoic acids were synthesised. Structures and purity of model compounds were confirmed by H-1 and C-13 NMR spectroscopy, as well as by HPLC and elemental analysis. Kinetics of base-catalysed hydrolysis of model phenyl esters occurring by the BAC2 mechanism were measured by UV spectrophotometry in 50% (v/v) aqueous dimethyl sulfoxide solutions at 25 degreesC under pseudo-first-order reaction conditions (c(NaOH) = 0.001-1.0 mol 1(-1)). Linear relation between J(_)(E) and log k(obs) with the slope close to unity was found for all model compounds. Neither one-parameter nor multiparameter Hammett-type description of variability of experimental data obtained for phenyl esters of 2-substituted benzoic acids was found. Two groups (conjugating and non-conjugating) were created by division of ortho-substituents in ortho-position using the AISE theory, based on their interaction with the reaction centre.