Nucleophilic Substitution at a Four-Coordinate Sulfur Atom: VI. Reactivity of Oximate Ions |
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Authors: | T M Prokop'eva Yu S Simanenko I P Suprun V A Savelova T M Zubareva and E A Karpichev |
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Institution: | (1) Ukrainian National Academy of Sciences, Litvinenko Institute of Physical Organic and Coal Chemistry, ul. R. Luxemburg 70, Donetsk, 340114, Ukraine |
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Abstract: | The kinetics of the reaction of oximate ions with 2,4-dinitrophenyl p-toluenesulfonate, 4-nitrophenyl p-toluenesulfonate, diethyl 4-nitrophenyl phosphate, and ethyl 4-nitrophenyl ethylphosphonate in H2O-DMSO mixtures (0 to 95 vol % of DMSO) cannot be described in terms of a single Bro/nsted equation. Regardless of the nature of the reaction center and leaving group, both in water and in 80% DMSO fast leveling of the reactivity of oximate ions is observed, the -effect decreases at pK
a 9.0 and disappears at pK
a 12.0 owing to difference in the solvation of weakly (pK
a 9.0) and strongly basic (pK
a 9.0) oximate ions rather than to change of the transition state. Just unfavorable solvation effects are responsible for the fact that the limiting nucleophilic reactivity of oximate ions (as typical -nucleophiles) is not higher than the reactivity of strongly basic alkoxide ions. |
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