POLYFUNCTIONAL CATALYSIS .3. TAUTOMERIC CATALYSIS

A tautomeric catalyst is a molecule that repeatedly cycles between two tautomeric states in the course of catalyzing a chemical reaction. The stoichiometries and kinetics for four different tautomeric catalysts-2-pyridone, benzoic acid, pyrazole, and 1,2,4-triazole-were examined for the aminolysis of 4-nitrophenyl acetate by n-butylamine and glycine ethyl ester in benzene and 1.5% methanol-benzene. The rate law is third order, rate = k[4-nitrophenyl acetate][amine][catalyst], and conforms to a reaction with the following stoichiometry: 4-nitrophenyl acetate + amine + catalyst %→amide + 4-nitrophenoI + catalyst. The rate constants at 25 ° for the above four tautomeric catalysts are (a) n-butylamine, 17, >2, 0.21, and 0.87 M-2 sec-1, respectively, and (b) glycine ethyl ester, 0.80, 0.36, 0.0086, and 0.021 M-2 sec-1, respectively. 2-Aminophenol exhibited no catalytic activity for the aminolysis of 4-nitrophenyl acetate by n-butylamine. Tautomeric catalysis appears to be a general phenomenon in acyl-transfer reactions. © 1969, American Chemical Society. All rights reserved.