Variation of the temperature‐dependent substituent effects with solvent in alkaline hydrolysis of substituted phenyl and alkyl benzoates and phenyl tosylates

The second‐order rate constantskfor the alkaline hydrolysis of eight substituted alkyl benzoates have been measured spectrophotometrically in aqueous 5.3 M NaClO4and 0.5 Mn‐Bu4NBr at various temperatures. Variation of the substituent effect with temperature in alkaline hydrolysis ofortho‐,meta‐, andpara‐substituted phenyl benzoates, phenyl tosylates, and alkyl benzoates in various solvents (water, aqueous 0.5 M Bu4NBr, 80% (v/v) DMSO, 2.25 M Bu4NBr, and 5.3 M NaClO4) was studied. The susceptibility to temperature variation of themetaandparapolar substituent effect, theorthoinductive effect, and the alkyl polar effect for various media showed good correlation with the solvent electrophilicity,ES, which characterizes the hydrogen‐bond donating power of the solvent. The variation of the temperature‐dependentorthoinductive effect with solvent hydrogen‐bond donor capacity (electrophilicity) was found to be nearly twice smaller than that formetaandparapolar effect. The temperature‐dependent alkyl polar substituent effect was found to vary withESnearly by the same extent as the polar effect ofmetaandparasubstituents. The dependences of theρvalues (altogether 109 values ofρ) on the (1/T) term for various media were found to cross nearly at the same isosolvent temperature (1/βisosolv ≈ 2 × 10−3) formeta‐,para‐,ortho‐, and alkyl‐substituted esters. AtT = βisosolvthe difference (ρ)S − (ρ)Waterbecomes zero for all polar substituent effects in all media considered and the additional inductive effect from theorthoposition (compared withparaderivatives) disappears for all solvents studied.