STANDARD ENTHALPY OF FORMATION OF LORNOXICAM AND ITS ANION L- IN AQUEOUS SOLUTION

Abstract

Lornoxicam was chosen as the object of our research. It is a derivative of thienothiazine monocarboxylic acid amide. It plays the role of a nonsteroidal anti-inflammatory drug, a non-narcotic analgesic and an antipyretic. Lornoxicam is practically insoluble in water. The heat of dissolution of crystalline lornoxicam in solutions of potassium hydroxide at 298.15 K was measured by direct calorimetric method. Measurements were carried out on a calorimeter with an isothermal shell and automatic recording of the temperature-time curve, in a reaction vessel with a volume of 60 cm3 and at T = 298.15 ± 0.01 K and P = 100.5 ± 0.7 kPa. The relative measurement error for the heat of dissolution of the standard substance was 0.1-0.3%. The operation of the calorimetric unit was tested according to the generally accepted calorimetric standard – the heat of dissolution of crystalline potassium chloride in water. The calculation of the equilibrium composition of the system, taking into account the processes of stepwise dissociation of lornoxicam and dissociation of water, was carried out according to the KEV program. The value of the standard enthalpy of lornoxicam formation was calculated using an additive group method based on group systematics with a classification of fragments of the Benson classification type, which takes into account the influence of the initial environment for atoms. The standard enthalpy of lornoxicam anion formation in an aqueous solution was determined using data on the heat of dissolution of lornoxicam in alkali solutions with a ratio of equivalents of at least 1:2. The standard enthalpy of lornoxicam formation and its dissociation products in an aqueous solution are calculated. The values of the standard enthalpy of lornoxicam formation and its dissociation products in an aqueous solution were obtained for the first time. They are key quantities in the thermochemistry of this compound, open up the possibility of conducting rigorous thermodynamic calculations in systems with lornoxicam.