Kinetics and Some Equilibria of Transacylation between Oxy Anions in Aprotic Solvents

Article abstract of DOI:10.1021/jo00133a001

β-Deuterium isotope effects (β-DIE) determined in acetonitrile for the following reactions are: CH3COO^- + 4-NO2C6H4O2CCL3 (L = H, D) (PNPA-L3), 0.958 +/- 0.007 (5-45 deg C); CH3COO^- + 2,4-(NO2)2C6H3O2CCL3 (DNPA-L3), 0.964 +/- 0.011 (5-20 deg C; OH(1-) + PNPA-L3, 0.972 +/- 0.028 (25 deg C); 4-NO2C6H4O^- (PNP^-) + CL3COOCOCL3, 1.00 +/- 0.02 (20 deg C); 4-NO-C6H4O^- (PNOP^-) + CL3COOCOCL3, 1.00 +/- 0.03 (20 deg C). β-DIEs in benzene for two of these reactions are: CH3COO^- + PNPA-L3, 0.957 +/- 0.045 (10-20 deg C); CH3COO^- + DNPA-L3, 0.985 +/- 0.050 (5-10 deg C).The fraction of tetrahedral character at the transition state (TS) deduced from β-DIEs for reactions of CH3COO^- + PNPA is 0.32 in both CH3CN and benzene, of CH3COO^- + DNPA is 0.28 in CH3CN and 0.12 in benzene, and of OH^- + PNPA is 0.21 in CH3CN.These values are similar to what is found in water and indicate TSs of essentially trigonal geometry.Isotope effects (CH3)2/k^(CD3)2> of unity for ester formation from CL3COOCOCL3 with phenoxides might be interpreted by two contributing factors to the observed effect; one of the usual hyperconjugation source and the other from electoststic effect of the label in the departing CL3COO^-.An equilibrium isotope effect (CH3)2/K^(CD3)2> of 1.03 in the direction of ester formation is calculated.A Hammett correlation of reactions of substituted phenoxides with CH3COOCOCH3 in CH3CN yielded ρ = -2.54.The reaction of CH3COO^- in CH3CN could not be effected with phenyl acetate.The reaction was endergonic (ΔG⁰ = +2.59 kcal/mol)with PNPA and exergonic (ΔG⁰ = -7.61 kcal/mol) with DNPA.Activation enthalpies of these reactions decrease from H2O to CH3CN to benzene, whereas activation entropies increase in this order.