Thermal Behaviour of Diclofenac Sodium: Decomposition and Melting Characteristics

• Published in: Chemical & pharmaceutical bulletin Vol. 49; no. 10; pp. 1245 - 1250
• Main Authors: TUDJA, Petar, KHAN, M. Zahirul I., MEŠTROVIC, Ernest, HORVAT, Michaela, GOLJA, Petra
• Format: Journal Article
• Language: English
• Published: Tokyo The Pharmaceutical Society of Japan 2001; Maruzen
• Subjects: Biological and medical sciences; Bones, joints and connective tissue. Antiinflammatory agents; Calorimetry, Differential Scanning; Chromatography, Thin Layer; degraded product; Diclofenac - chemistry; diclofenac sodium; Hot Temperature; Medical sciences; Pharmacology. Drug treatments; Spectroscopy, Fourier Transform Infrared; Temperature; thermal decomposition; thermal oxidation; Thermogravimetry; Differential scanning calorimetry; Prostaglandin-endoperoxide synthase; Fourier transformation; Chemical analysis; Enzyme; Thermogravimetry; Enzyme inhibitor; Thermal reaction; Thermal stability; Diclofenac; Non steroidal antiinflammatory agent; Infrared spectrometry; Thin layer chromatography; Analgesic; Arylacetic acid derivatives; Cyclization; Antipyretic; Oxidation; Oxidoreductases; Thermal analysis; Degradation product
• ISSN: 0009-2363; 1347-5223
• DOI: 10.1248/cpb.49.1245

The thermal behaviour and melting characteristics of diclofenac sodium were investigated using various instrumental techniques—differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) spectroscopy and thin layer chromatography (TLC). DSC analysis of diclofenac sodium performed under dynamic flow of either synthetic air or helium or nitrogen did not produce any sharp endothermic peak characteristic of melting peak of a pure substance. Both the rate of scanning of the sample and the environmental atmospheric condition significantly affected the thermographic profile of diclofenac sodium. An exothermic peak prior to an endothermic peak corresponding to melting of the substance appeared when heated under dynamic flow of synthetic air suggesting oxidation (decomposition) of diclofenac sodium before reaching its melting point. In fact, at a scanning rate of 1 °C/min only the exothermic peak appeared in the thermogram, suggesting complete decomposition prior to melting under the dynamic flow of synthetic air. DSC, FT-IR and TLC data obtained from samples heated under the dynamic flow of either helium or nitrogen revealed formation of a related compound, 1-(2,6-dichlorophenyl)-indolin-2-one, an indol-cyclic amide, as a result of an intramolecular cyclization reaction during the heating process. TGA data demonstrated a loss of 11.4—20.2% of the mass of diclofenac sodium when heated under various environmental conditions, and also supported the oxidative nature of degraded product(s) when the thermal process occurred slowly under a dynamic flow of synthetic air.