Aminolyses of 2,4-Dinitrophenyl and 3,4-Dinitrophenyl 2-Furoates: Effect of ortho-Substituent on Reactivity and Mechanism

摘要

Second-order rate constants (k_N) have been measured spectrophotometrically for reactions of 3,4-dintrophenyl 2-furoate (2) with a series of secondary alicyclic amines in 80 mol % H₂O/20 mol % dimethyl sulfoxide (DMSO) at 25.0∩. The Br┆nsted-type plot exhibits a downward curvature for the aminolysis of 2, which is similar to that reported for the corresponding reactions of 2,4-dintrophenyl 2-furoate (1). Substrate 2 is less reactive than 1 toward all the amines studied but the reactivity difference becomes smaller as the amine basicity increases. Dissection of the second-order rate constants into the microscopic rate constants has revealed that the reaction of 2 results in a smaller k₂/k_?1 ratio but slightly larger k₁ value than that of 1. Steric hindrance has been suggested to be responsible for the smaller k₁ value found for the reactions of 1, since the ortho-substituent of 1 would inhibit the attack of amines (i.e., the k₁ process).