Hydrogen Bonding Interaction of the Mannich Base, 4-Nitro-2-[(diethylamino) methyl] Phenol with Amines

Spectral studies of the title compound showed that its intramolecular hydrogen bond is relatively strong. Hydrogen bond formation between some amines and the phenolic -OH group is not inhibited in presence of strong intramolecular hydrogen bonding between the -OH group and the ortho-diethylamino group in the title compound. Proton transfer equilibrium constants (KPT) between the studied compound and different amines in methylene chloride were measured. A linear correlation was found between log KPT and the proton affinities, PA, of amines except for α-picoline. The KPT values due to the proton transfer equilibrium between the Mannich base and α-picoline in different solvents were calculated and they gave a good correlation with the Onsager parameter. The estimated thermodynamic parameters showed that the proton transfer equilibrium in our system is entropy- and enthalpy controlled, and proved more polarizability of the intermolecular OHN bridge with increasing the solvent polarity.