A simultaneous TG-DTA study of the thermal decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester (salsalate)

摘要

Simultaneous thermogravimetry-differential thermal analysis (TG-DTA) and gas and liquid chromatography with mass spectrometry detection have been used to study the kinetics and decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester, commercially known as salsalate. Samples of salsalate were heated in the TG-DTA apparatus in an inert atmosphere (100 ml min(-1) nitrogen) in the temperature range 30-500degreesC. The data indicated that the decomposition of salsalate is a two-stage process. The first decomposition stage (150-250degreesC) had a best fit with second-order kinetics with E-a = 191-198 kJ/mol. The second decomposition stage (300-400degreesC) is described as a zero-order process with E-a = 72-80 kJ/mol. The products of the decomposition were investigated in two ways:(a) Salsalate was heated in a gas chromatograph at various isothermal temperatures in the range 150-280degreesC, and the exit gas stream analyzed by mass spectrometry (GC-MS). This approach suggested that salsalate decomposes with the formation of salicylic acid, phenol, phenyl salicylate, and cyclic oligomers of salicylic acid di- and tri-salicylides.(b) One gram samples of salsalate were heated in a vessel under nitrogen to 150degreesC, and the residues were analyzed by liquid chromatography-mass spectrometry (LC-MS). The major compound detected was a linear tetrameric salicylate ester. (C) 2003 Elsevier B.V. All rights reserved.