Solid–liquid phase equilibria in binary systems with paracetamol

Solid–liquid equilibria in three binary systems of paracetamol (PAR), namely with phenylephrine hydrochloride (PEP.HCl), tramadol hydrochloride (TMD.HCl) and ibuprofen (IBU), were studied by differential scanning calorimetry (DSC). All three systems exhibit eutectic behaviour with the eutectic temperatures 386.1 ± 0.4 K (PAR-PEP.HCl), 355.6 ± 1.2 K (PAR-TMD.HCl) and 348.1 ± 0.2 K (PAR-IBU). The eutectic enthalpy versus composition (Tammann) plots were constructed for the PAR-PEP.HCl and PAR-TMD.HCl systems and the compositions of the eutectic melts x PAR = 0.46 (PAR-PEP.HCl) and x PAR = 0.64 (PAR-TMD.HCl) were determined. DSC data were used to assess the parameters of Redlich–Kister equation for the excess Gibbs energy of binary melts. While the PAR-PEP.HCl and PAR-TMD.HCl melts show a negative deviation from ideality, the PAR-IBU melt exhibits a positive one. Binary phase diagrams of these systems were calculated using evaluated thermodynamic data, and the eutectic melts compositions are x PAR = 0.48 (PAR-PEP.HCl), x PAR = 0.59 (PAR-TMD.HCl) and x PAR = 0.013 (PAR-IBU).