Thermodynamic properties and low-temperature X-ray diffraction of vitamin B3

Abstract

In the present work temperature dependence of heat capacity of vitamin B3 (nicotinic acid) has been measured for the first time in the range from 5 to 346K by precision adiabatic vacuum calorimetry. Based on the experimental data, the thermodynamic functions of the vitamin B3, namely, the heat capacity, enthalpy H°(T) – H°(0), entropy S°(T) – S°(0) and Gibbs function G°(T) – H°(0) have been determined for the range from T→0 to 343K. The value of the fractal dimension D in the function of multifractal generalization of Debye’s theory of the heat capacity of solids was estimated and the character of heterodynamics of structure was detected. The thermodynamic parameters ΔfS°, ΔfG° at T=298.15K and p=0.1MPa have been calculated. The thermodynamic analysis of reactions involving nicotinic acid was made. The low-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion.