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Abstract

The second-order rate constants k₂ (l mol^-1 s^-1) for the alkaline hydrolysis of meta-, para- and ortho-substituted phenyl benzoates C₆H₅CO₂C₆H₄-X and phenyl tosylates 4-CH₃-C₆H₄SO₂OC₆H₄-X in aqueous 5.3 M NaClO₄ have been measured spectrophotometrically at various temperatures. The log k values at a single temperature were analysed according to the equations log k_m,p = log k₀ + (ρ)°_m,pσ°, log k_ortho = log k₀+ (ρ_I)_orthoσ_I + (ρ_R)_orthoσ_R° + δ_orthoυ and log k_m,p,ortho = log k₀+ (ρ_I)_orthoσ_I + (ρ_I)_metaσ_I + (ρ_I)_paraσ_I + (ρ_R)_orthoσ_R° + (ρ_R)_metaσ_R° + (ρ_R)_paraσ_R° + δ_orthoυ. In the case of various temperatures, the equation for data processing involved the additional c₁(1/T) term and the cross term c_m,p(1/T)σ° or c₂(1/T)σ_I and c₃(1/T)σ_R° different for ortho-, meta- and para-substituted derivatives. As the measure of the steric influence from ortho position, the Charton υ values were used. In the case of a single temperature, the sensitivity to the inductive effect of ortho substituents was found to be about 1.7 times (in water 1.5 times) stronger than that of para and meta substituents in both reaction series studied. The variation of the ortho inductive influence with temperature appeared to be more than twice larger than that for para substituents. Compared to water, in aqueous 5.3 M NaClO₄ the inductive effect from ortho position was nearly unchanged while the para inductive effect was found to be about 0.13 units of ρ_I smaller in the case of both reaction series studied, though the polar effects in these reaction series differ about two-fold. Due to different variation of the ortho and para inductive effects with solvent and temperature, the relative increase in the ortho effect was observed when going from water to aqueous 5.3 M NaClO₄.

Keywords: Esters; Phenyl benzoates; Phenyl tosylates; Alkaline hydrolysis; Substituent effects; ortho Effects; Kinetics; Chemometrics; Steric effect.

References: 40 live references.