THE EFFECT OF ALKALI-METAL IONS ON NUCLEOPHILIC-SUBSTITUTION REACTIONS OF P-NITROPHENYL AND M-NITROPHENYL 2-THIOPHENENATES WITH ALKALI-METAL ETHOXIDES IN ABSOLUTE ETHANOL

Rate constants have been measured spectrophotometrically for the react ions of p- and m-nitrophenyl 2-thiophenecarboxylate (5a and 5b, respec tively) with alkali metal ethoxides (EtO(-)M(+)) in absolute ethanol a t 25.0+/-0.1 degrees C. The reactivity of EtO(-)M(+) exhibits dependen ce on the size of alkali metal ions, ie. the reactivity of EtO(-)M(+) toward 5a decreases in:he order EtO(-)K(+)greater than or equal to EtO (-)Na(+)>EtO(-)Li(+)>EtO(-), while the one toward 56 does in the order EtO(-)Na(+)greater than or equal to EtO(-)K(+)>EtO(-)Li(+)>EtO(-). Th is result indicates that ion paired EtO(-)M(+) is more reactive than d issociated EtO(-), and alkali metal ions form complexes with the subst rate more strongly at the transition state than at the ground state. T he catalytic effect shown by alkali metal ions appears to be less sign ificant in the reaction of 5 than in the corresponding reaction of 4, indicating that complexation of alkali metal ions with 5 is not as str ong as the one with 4.