Investigation on the thermal behavior of beta-blockers antihypertensives atenolol and nadolol using TG/DTG, DTA, DSC, and TG-FTIR

摘要

Thermal behavior of beta-blocker antihypertensives nadolol and atenolol was investigated using TG/DTG, DTA, and DSC, under dynamic nitrogen and air atmosphere. Nadolol decomposed in a single mass loss step between 196 and 353 A degrees C, after melting at 128.0 A degrees C. In air, an additional event related to the burning of carbonaceous material was observed. Under nitrogen atenolol decomposed also in a single step from 191.8 to 900 A degrees C. However the DTG revealed that this decomposition splits in two successive events resulting in a residue of 17.2 % at the end of the run, with a melting peak at 153.1 A degrees C. In air, an additional step referent to the burning of carbonaceous residue can be seen. Although both presented melting events, only atenolol crystallized on cooling. Evolved gas analysis by TG-FTIR revealed that nadolol decomposes via terc-butylamine releasing, while atenolol loses ammonia in a nonpreviously reported dimerization reaction after melting with a consecutive isopropylamine releasing. A tentative thermal behavior mechanism is presented for both cases.