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/2O mol % dimethyl sulfoxide (DMSO) at 25.0 °C.The Br0nsted-type plot exhibits a downward curvature for the arninolysis 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).