Low-temperature heat capacities and standard molar enthalpy of formation of aspirin

Molar heat capacities (C _p,m) of aspirin were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 383 K. No phase transition was observed in this temperature region. The polynomial function of C _p,m vs. T was established in the light of the low-temperature heat capacity measurements and least square fitting method. The corresponding function is as follows: for 78 K≤T≤383 K, C _p,m/J mol^-1 K^-1=19.086X ⁴+15.951X ³-5.2548X ²+90.192X+176.65, [X=(T-230.50/152.5)]. The thermodynamic functions on the base of the reference temperature of 298.15 K, {ΔH _T -ΔH _298.15} and {S _T-S _298.15}, were derived. Combustion energy of aspirin (Δ_c U _m) was determined by static bomb combustion calorimeter. Enthalpy of combustion (Δ_c H ^o _m) and enthalpy of formation (Δ_f H ^o _m) were derived through Δ_c U _m as - (3945.26±2.63) kJ mol^-1 and - (736.41±1.30) kJ mol^-1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.