Calorimetric study and thermal analysis of crystalline nicotinic acid

As one primary component of Vitamin B₃, nicotinic acid pyridine 3-carboxylic acid] was synthesized, and calorimetric study and thermal analysis for this compound were performed. The low-temperature heat capacity of nicotinic acid was measured with a precise automated adiabatic calorimeter over the temperature rang from 79 to 368 K. No thermal anomaly or phase transition was observed in this temperature range. A solid-to-solid transition at T _trs=451.4 K, a solid-to-liquid transition at T _fus=509.1 K and a thermal decomposition at T _d=538.8 K were found through the DSC and TG-DTG techniques. The molar enthalpies of these transitions were determined to be Δ_trs H _m=0.81 kJ mol^-1, Δ_fus H _m=27.57 kJ mol^-1 and Δ_d H _m=62.38 kJ mol^-1, respectively, by the integrals of the peak areas of the DSC curves. This revised version was published online in August 2006 with corrections to the Cover Date.