Standard enthalpy of formation and heat capacities of 3,5-di-tert-butylsalicylic acid

The constant volume energy of combustion of crystalline 3,5-di-tert-butylsalicylic acid (t-BSA) in oxygen at 298.15 K was determined using combustion calorimeter to be −8292.57±2.51 kJ mol−1. The standard molar enthalpies of combustion and formation of 3,5-di-tert-butylsalicylic acid were derived, at T=298.15 K, ΔcHmΘ=−8302.48±2.51 kJ mol−1 and ΔfHmΘ=−744.30±3.21 kJ mol−1, respectively. The heat capacities of the compound were measured with an adiabatic calorimeter over the temperature range from 79 to 351 K. No indication of any phase transition or thermal anomaly was observed in this temperature range. The fusion and evaporation behavior of the compound were examined by thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The molar enthalpy and entropy of fusion, ΔfusHmΘ and ΔfusSmΘ, at T=437.5 K, were determined to be 22.92±0.55 kJ mol−1 and 139.4±3.3 J mol−1 K−1, respectively; and the molar enthalpy and entropy of evaporation, ΔvapHmΘ and ΔvapSmΘ, at T=477.5 K, were obtained as 83.88±2.1 kJ mol−1 and 341.7±8.4 J mol−1 K−1, respectively.