Determination of dissociation constants and thermodynamic parameters of pyrimidine derivatives in organic-water mixed solvents at different temperatures

Two novel pyrimidine derivatives have been synthesized and their structures have been confirmed by IR, 1H NMR and mass spectral data. The dissociation constants of these two compounds; 4-(naphthalen-1-yloxy)-N-(p-tolyl) pyrimidin-2-amine (TP-1) and N-(4-fluoro phenyl)-4-(naphthalen-1-yloxy) pyrimidin-2-amine (FP-1) were studied in methanol/DMF - water (60:40 v/v) solvent systems at different temperatures ranging from 25 °C to 45 °C at a 10 °C interval using the Calvin-Bjerrum pH titration method. The results are interpreted in terms of substituent present in the compounds. Furthermore, some thermodynamic parameters such as enthalpy (∆H°), Gibb's free energy (∆G°) and entropy (∆S°) of these dissociations have also been evaluated at different temperatures from dissociation constant data.