Accelerated Cleavage of Glycine p-Nitrophenyl Ester in an Aqueous Medium by a Crown Ether Compound

Macrocyclic crown ether carboxylates have been investigated as catalytic host molecules for the ester cleavage reaction of guest glycine p-nitrophenyl ester ammonium ion (3-NH3+) in an aqueous medium. The result for 3,5-dimethylylbenzoate-18-crown-5 (1c) shows p-nitrophenol release similar to that of added simple substituted benzoates, whereas 2,6-dimethylylbenzoate-18-crown-5 (2c) shows a significant acceleration of the reaction rate. To aid in interpretation of these observations, rates of complexation and molar equilibrium constants (K) for closely related amino acid structures were obtained with 18-crown-6 and 18-crown-5 using an ultrasonic absorption technique.