期刊
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
卷 18, 期 11, 页码 1138-1144出版社
WILEY
DOI: 10.1002/poc.967
关键词
esters; phenyl benzoates; alkaline hydrolysis; substituent effects; ortho effects; solvent effects; kinetics
The second-order rate constants k(2) (M-1 s(-1)) for the alkaline hydrolysis of meta-, para- and ortho-substituted phenyl benzoates, C6H5CO2C6H4X, in aqueous 0.5 M n-BU4NBr were measured spectrophotometrically. The dependence of substituent effects, especially ortho inductive, resonance and steric terms on different solvent parameters, was studied using the following equation: Delta log k(ortho) = c(0) + c(1) ((ortho))sigma(I) + c(2)((ortho))alpha(0)(R) + c(3)((ortho))E-s(B) + c(4)Delta E + c(5)Delta Y + c(6)Delta P + c(7)((ortho))Delta E sigma(I) + c(8)((ortho))Delta Y sigma(I) + c(9)((ortho))Delta P sigma(I) + c(10)((ortho))Delta E sigma(0)(R) + c(11)((ortho))Delta Y sigma(0)(R) + c(12)((ortho))Delta P sigma(0)(R) where Delta log kappa = log k(x) -log k(H), sigma(I), sigma(0)(R) and E-s(B) are the inductive, resonance and steric substituent constants and E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In data treatment Delta E = Es - E-H2O, Delta Y = Y-s - Y-H2O and Delta P = P-S - P-H2O 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 Es was found to be ca threefold smaller than that for para substituents, whereas the ortho resonance term appeared to vary with solvent very similarly to that for para substituents. The steric term of ortho substituents was found to be approximately independent of solvent parameters. 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 that of 60% aqueous ethanol (E approximate to 13.3). Copyright (c) 2005 John Wiley & Sons, Ltd.
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