Base-Catalyzed Acyl Exchange Reactions of N,O-Diacyl-o-aminophenols. Substituent and Temperature Effects on the Equilibrium Constants

Article abstract of DOI:10.1246/bcsj.69.775

Substituent and temperature effects on the equilibrium constants for the triethylamine-catalyzed acyl exchange reactions of N-(substituted benzoyl)-O-acetyl-o-aminophenols have been investigated by ¹HNMR spectroscopy. It was found that the standard enthalpy change ΔH^o in acyl exchange processes, estimated from temperature dependence of the equilibrium constant, correlates well with the standard free energy change ΔG^o which was used as a measure of the relative stability of isomer pairs, while the standard entropy change ΔS^o is approximately constant (-6±2 J K^-1 mol^-1) irrespective of the substituems in benzoyl introduced. The finding of enthalpy-controlled acyl exchange reactions confirms that the relative stability of a given isomer pair is determined by the difference in electrostatic force of attraction between the amide nitrogen with a partial positive charge and the ester carbonyl oxygen having a partial negative charge in both isomers.