51074-95-4Relevant articles and documents
Polyelectrolyte-Catalyzed Acetyl Transfer Reactions. Structure-Reactivity Relationships in the Aminolysis of Phenyl Acetates by Poly(ethyleneimine) and Glycylglycine.
Arcelli, Antonio,Concilio, Carlo
, p. 201 - 226 (2007/10/02)
The aminolysis of a wide series of substituted phenyl acetates by poly(ethyleneimine) (PEI) is studied.Saturation kinetics are observed and the ester-polyamine association equilibrium constants, as well as the rates of decomposition of the resulting intracomplexes, are determined.Unlike the association constants, the rate constants for the reaction of the intracomplex are found to depend on the acidity of the leaving groups.Two Broensted-type relationships are found for anionic and neutral esters having different intercepts but proximate slopes -0.73 and -0.77 respectively, which decrease to lower values with very reactive phenyl acetates.Only one broken Broensted relationship is found for the bimolecular aminolysis by glycylglycine.The results are consistent with the formation of a tetrahedral intermediate by the amino groups of PEI, with a change in the rate-determining step for very reactive esters from the breakdown to the formation of the tetrahedral intermediate.The higher reactivity of PEI, which is more relevant with substrates containing anionic groups, is principally ascribed to the electrostatic polyelectrolyte-substrate binding.A minor role is played by the increase in the acidity of the conjugate acid of the leaving group, i.e. of its leaving ability, caused by the association of the ester with PEI: values of effective molarity in the range of 10 to 15 mol cm-3 are found.
