THE EFFECT OF ALKALI-METAL IONS ON NUCLEOPHILIC-SUBSTITUTION REACTIONS OF ARYL SUBSTITUTED BENZENESULFONATES

Rate constants have been measured spectrophotometrically for the nucle ophilic substitution reactions of aryl substituted benzenesulfonates ( 3) with alkali metal ethoxides (EtO-M+) and butane-2,3-dione monoximat es (Ox-M+) in ethanol at 25-degrees-C. The reactivity of the alkali me tal ethoxides decreases in the order EtO-K+>EtO->EtO Li+, indicating t hat K+ ion behaves as a catalyst and Li+ ion acts as an inhibitor for all the substrates studied. For the corresponding reactions of 3 with Ox-M+, Li+ ion also exhibits inhibitory effect for all the substrates, while, K+ ion shows catalytic or inhibitory effects depending on the nature of substituents on the acyl and phenyl moieties. A study of sub stituent effect on rate has revealed that both EtO- and Ox- systems ha ve the same reaction mechanism. The different behavior shown by K+ ion for the reaction of 3 with EtO- and Ox- would be attributed to a diff erence in charge polarization of S=O bond in the transition state betw een the two systems and/or a change in conformation of Ox-K+.