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Abstract

The second-order rate constants k (in dm³ mol^–1 s^–1) for alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H₄CO₂C₆H_5, have been measured spectrophotometrically in aqueous 0.5 and 2.25 M Bu₄NBr at 25 °C. The substituent effects for para and meta derivatives were described using the Hammett relationship. For the ortho derivatives the Charton equation was used. For ortho-substituted esters two steric scales were involved: the E_sB and the Charton steric (υ) constants. When going from pure water to aqueous 0.5 and 2.25 M Bu₄NBr, the meta and para polar effects, the ortho inductive and resonance effects in alkaline hydrolysis of phenyl esters of substituted benzoic acids, became stronger nearly to the same extent as found for alkaline hydrolysis of C₆H₅CO₂C₆H₄-X. The steric term of ortho-substituted esters was almost independent of the media considered. The rate constants of alkaline hydrolysis of ortho-, meta- and para-substituted phenyl benzoates (X-C₆H₄CO₂C₆H₅, C₆H₅CO₂C₆H₄-X) and alkyl benzoates, C₆H₅CO₂R, in water, 0.5 and 2.25 M Bu₄NBr were correlated with the corresponding IR stretching frequencies of carbonyl group, (Δν_CO)_X.

Keywords: Esters; Phenyl benzoates; Alkaline hydrolysis; Kinetics; ortho-Effect; Substituent effects; Hammett equation; IR stretching frequencies of carbonyl group.

References: 31 live references.