Abstract
Pyridoxine, as well as its derivatives, are the main forms of vitamin B6, which plays extremely important biological roles in living organisms. In our work, the enthalpies of dissolution of crystalline pyridoxine and pyridoxal-5'-phosphate in water and in aqueous solutions of KOH at 298.15 K were measured by a direct calorimetric method in a wide concentration range. The measurements were carried out on a calorimeter with an isothermal shell and automatic recording of the temperature-time curve. The values of the standard enthalpies of combustion and formation of pyridoxine and pyridoxal-5'-phosphate were calculated using the additive group method based on the group systematics with the classification of fragments like the Benson classification, which takes into account the effect of the primary environment for atoms. The standard enthalpies of formation of pyridoxine and pyridoxal-5'-phosphate and the products of their dissociation in an aqueous solution were calculated. (C) 2021 Elsevier B.V. All rights reserved.