Aminolyses of 2,4-dinitrophenyl and 3,4-dinitrophenyl 2-furoates: Effect of ortho-substituent on reactivity and mechanism

Abstract

Second-order rate constants (kN) 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 °C. The Brønsted-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).