AMINOLYSIS OF ACTIVATED ESTERS OF INDOLE-3-ACETIC-ACID IN ACETONITRILE

Seven activated esters of indole-3-acetic acid (IAA) [4-oxo-1,2,3-benzotriazin-3-yl indole-3-acetate (IAA-3HBO), succinimido indole-3-acetate (IAA-NHS), 5-norbornene-1,3-dicarboximido indole-3-acetate (IAA-NHND), phthalimido indole-3-acetate (IAA-NHP), naphthalimido indole-3-acetate (IAA-NHN), 4-nitrophenyl indole-3-acetate (IAA-4NP), 8-quinolyl indole-3-acetate (IAA-8HQ)] were prepared and characterized. Their kinetics of aminolysis with butylamine, piperidine, and pyrrolidine in acetonitrile were investigated. In general, the observed pseudo-first-order rate constants, k(obs), fit the two-term rate equation k(obs) = k1[amine] + k2[amine]2. For the aminolysis of six of the esters with piperidine there was no measurable k2 term. The 8-hydroxyquinoline ester and N-hydroxynaphthalimide ester of indole-3-acetic acid had no measurable k2 term for aminolysis with either pyrrolidine or piperidine. In general, the reactivity of the esters increased with increasing acidity of the conjugate acid of the nucleofuge and with increasing base strength of the nucleophilic amine. The IAA ester of NHP was observed to be ca. 100-fold more reactive than the IAA ester of 4NP although the pK(a)'s of the leaving groups are nearly the same. In all cases low activation energies were observed.