Thermodynamic properties of vitamin B9

•Temperature dependence of heat capacity of vitamin B9 has been measured by precision adiabatic vacuum calorimetry.•The thermodynamic functions of the vitamin B9 have been determined for the range from T → 0 to 333 K.•The character of heterodynamics of structure was detected.•Enthalpy of combustion of the vitamin B9 was measured using high-precision combustion calorimeter.

In the present work temperature dependence of heat capacity of vitamin B9 (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 B9, 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 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) kJ·mol−1 of the vitamin B9 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 B9 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.

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