Thermochemical investigation of the (phosphonic acid + N,N-dimethylformamide) system at T = (298.15 to 328.15) K

Highlights: • The solution and dilution enthalpies of H₃PO₃ in DMF were measured over the wide concentration range. • The heat capacity of crystalline phosphonic acid was determined. • The standard solution enthalpies of ionic and molecular H₃PO₃ in DMF are negative and depend weakly on the temperature. - Abstract: For the first time the solution enthalpies of crystalline phosphonic acid (H₃PO₃) in N,N-dimethylformamide (DMF) and dilution enthalpies of the acid solutions in DMF (H₃PO₃ concentrations: x₂ < 0.781 molar fraction or m < 49 mol/kg) in pure DMF have been measured at T = (298.15, 308.15, 318.15, and 328.5) K. The temperature dependence of the heat capacity of crystalline H₃PO₃ was obtained also for the first time. The standard solution enthalpies of H₃PO₃ in DMF have been calculated at different temperatures according to two different models considering the phosphonic acid either as a weak electrolyte dissociating by the first stage or as a non-electrolyte able to form dimmers. A number of thermodynamic properties have been evaluated.