Synthesis and physicochemical properties of polyhydroxylated diphenyl ethers

Five polyhydroxylated diphenyl ethers (PHODEs) were synthesized. The first ionization constants (pKa1) of the synthesized compounds and seven phenolic compounds were determined using potentiometric titration experiments, together with the software ACD/Labs pKa DB program (version 6.0). The compared results showed that the software could be used to predict the pKa1 of all 209 PHODEs. The thermodynamic properties of 209 PHODEs were calculated using density functional theory (DFT) at the B3LYP/6-311G** level with Gaussian 09 program. The standard enthalpy of formation (ΔfHθ) and the standard Gibbs energy of formation (ΔfGθ) were obtained. Two types of hydrogen bond were found to exist in the PHODEs' molecules. The intramolecular hydrogen bond energies were discussed. The relative stability of PHODEs isomers was proposed theoretically with the relative standard Gibbs energy of formation (ΔfGRθ). The relationships of Sθ, ΔfHθ and ΔfGθ to the number and position of the hydroxyl substitution (NPHOS) were studied.