Aminolysis of Phenyl-Esters by Microgel and Dendrimer Molecules Possessing Primary Amines

Microgels containing primary amino functions were prepared by a water-in-oil emulsion polymerisation technique from an aminoethyl acrylate, acrylamide and methylene-bis-acrylamide polymer feed. Dendrimeric polyamines possessing twelve and six primary amino functions were prepared and their reactivities, together with that of the microgel, were measured against the Class 11 aminolysis of substituted phenyl acetates. For comparison, the kinetics of aminolysis of ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine were measured. The kinetics obey simple second order rate laws against ester and amine concentrations. The absence of buffer catalysis and of kinetic rate laws showing higher powers of amine concentration indicate that the breakdown of the tetrahedral intermediate (the rate limiting step) does not require a second catalytic molecule. The reactivity per amino function against the phenyl esters is similar for each amino reagent, indicating that steric requirements of the microgel, which would be substantial due to its polymeric nature, are compensated by a catalytic function. The slope of the Hammett dependence for the reaction of substituted phenyl acetates with the amino-microgel is smaller than that for simple amine attack in Class II ester aminolysis, indicating that a smaller build-up of negative charge is occurring, consistent with electrophilic assistance.