Formation Kinetics of an Amino Carboxy Type Merostabilized Free Radical

Article abstract of DOI:10.1021/ja00527a036

The reduction of isatin (5) and N-methylisatin (6) by the merostabilized free radical 3,5,5-trimethyl-2-morpholinon-3-yl (4) to isatide (7) and N,N'-dimethylisatide (8) is described.The reaction rates are first order in the meso and dl dimers (2 and 3) of 4 and zero order in N-methylisatin.The rate of reaction is a measure of the rate of bond homolysis of the meso or dl dimer.Rate constants and activation parameters are reported.The free energies of activation for homolysis of 2 and 3 in chloroform solvent are 24.6+/-0.3 and 25.1+/-0.2 kcal/mol, respectively.The enthalpy of activation for recombination of 4 is estimated at 4-5 kcal/mol.Measured rate constants for bond homolysis were consistent within one standard deviation with the observed kinetics of isomerization of the meso dimer (2) to the equilibrium mixture of the meso and dl dimers.The activation parameters in part are a measure of the effect of merostabilization on radical stability.