Kinetic Study of Alkaline Hydrolysis of Substituted Phenyl Tosylates. XXII. Variation of Ortho Substituent Effect with Solvent
The second-order rate constants k (dm 3 mol - 1 s - 1 ) for the alkaline hydrolysis of meta-, para-, and ortho-substituted phenyl tosylates 4-CH 3 C 6 H 4 SO 2 OC 6 H 4 -X in aqueous 0.5 M Bu 4 NBr have been measured spectrophotometrically in a wide temperature range. The log k values for ortho-substituted derivatives at various temperatures together with meta- and para-substituted derivatives were analyzed using the modified Fujita-Nishioka equation log k m , p , o r t h o = c 0 + c 1 ( m , p , o r t h o ) σ° + C 2 ( o r t h o ) σ I + c 3 (1/T) + c 4 ( m , p , o r t h o ) (1/T)σ° + c 5 ( o r t h o ) (1/T)σ 1 . In order to study the dependence of substituent effects, especially ortho inductive and resonance terms on different solvent parameters, the following equation was used: Alog k m , p , o r t h o = c 0 + c 1 ( m , p , o r t h o ) σ° + c 2 ( o r t h o ) σ 1 + c 3 ΔE + c 4 ΔY + c 5 ΔP + c 6 ( m , p , o r t h o )ΔFσ° + + c 7 ( m , p , o r t h o ) ΔYσ° + c 8 ( m , p , o r t h o ) ΔPσ° + C 9 ( o r t h o ) ΔEσ I + c 1 0 ( o r t h o ) ΔYσ I + c 1 1 ( o r t h o ) ΔPσ I . Δlog k = 1og k X -log k H , σ° and σ I , are the Taft polar and inductive substituent constants, E, Y and P, are the solvent electrophilicity, polarity and polarizability parameters, respectively. In data treatment ΔE = E S - E H 2 O , ΔY = Y S - Y H 2 O , ΔP = P S - P H 2 O were used. The solvent electrophilicity was found to be the main factor responsible for changes in the ortho, para, and meta polar substituent effects with medium. The variation of the ortho inductive term with the solvent electrophilicity E S was found to be twice smaller than that for para substituents, while the ortho resonance term appeared to vary with solvent nearly similarly to that for para substituents. The ortho effect caused by the supplementary inductive effect from ortho position was found to disappear in a solvent whose electrophilic solvating power is comparable to pure DMSO (E 4).