Thermodynamic properties of vitamin B9

In the present work temperature dependence of heat capacity of vitamin B-9 (folic acid dihydrate) has been measured for the first time in the range from (6 to 333) K by precision adiabatic vacuum calorimetry. Based on the experimental values, the thermodynamic functions of the vitamin B-9, namely, the heat capacity, enthalpy H degrees(T) - H degrees(0), entropy S degrees(T) - S degrees(0) and Gibbs function G degrees(T) - H degrees(0) have been determined for the range from T ->(0 to 333) K. 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. Enthalpy of combustion (-8942.8 +/- 7.5) kJmol(-1) of the vitamin B-9 was measured for the first time using a high-precision combustion calorimeter. The standard molar enthalpy of formation in the crystalline state (-1821.0 +/- 7.9) kJ.mol(-1) of B-9 at 298.15 K was derived from the combustion experiments. Using a combination of the adiabatic and combustion calorimetry results, the thermodynamic functions of formation of the folic acid dihydrate at T = 298.15 K and p = 0.1 MPa have been calculated. The low-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion. (C) 2016 Elsevier Ltd. All rights reserved.