Reactions of Aryl 5-substituted-2-Thiophenecarboxylates Promoted by 4-Z-C6H4O-/4-Z-C6H4OH in 20 mol % DMSO(aq). Effect of Nucleophile on Acyl-Transfer Reaction

Abstract

Nucleophilic substitution reactions of 5-XC4H2(S)C(O)OC6H3-2-Y-4-NO2(1) promoted by 4-Z-C6H4O-/4Z-C6H4OH in 20 mol % dimethyl sulfoxide ( DMSO)(aq) have been studied kinetically. The reactions exhibited second-order kinetics with beta(acyl) = -2.52 to -2.83, rho(x) = 2.81-3.16, beta(nuc) = 0.88-0.04 and beta(lg) = -0.94, respectively. The results have been interpreted with an addition-elimination mechanism in which the nucleophilic attack occurs in the rate-determining step. Comparison with existing data reveals that the rate-determining step changes from the second to the first step by the change in the nucleophile from R2NH/R2NH2+ to 4-Z-C6H4O-/4-Z-C6H4OH.