Authors:Hermínio Digo, Susana Pinto, and Joaquim Moura Ramos
The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC).
The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10C min-1. The melting peak showed an onset at Ton = 144C (417 K) and a maximum intensity at Tmax = 152C (425 K), while the onset of the glass transition signal was at Ton = 6C. The melting enthalpy was found to be ΔmH = 28.90.3 kJ mol-1, and the heat capacity jump at the glass transition was ΔCP = 108.10.1 J K-1mol-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed
the determination of the activation energy at the glass transition temperature (245 kJ mol-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as ΔfHmo(C14H10O5, cr) = - (837.63.3) kJ mol-1, by combustion calorimetry.