Separation of ortho Inductive, Resonance and Steric Terms in Alkaline Hydrolysis of Substituted Phenyl Benzoates and Phenyl Tosylates

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 km,p = log k0 + (ρ)°m,pσ°, log kortho = log k0+ (ρI)orthoσI + (ρR)orthoσR° + δorthoυ and log km,p,ortho = log k0+ (ρI)orthoσI + (ρI)metaσI + (ρI)paraσI + (ρR)orthoσR° + (ρR)metaσR° + (ρR)paraσR° + δorthoυ. In the case of various temperatures, the equation for data processing involved the additional c1(1/T) term and the cross term cm,p(1/T)σ° or c2(1/T)σI and c3(1/T)σR° 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 ρI 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.