Study of thermal behavior of 1H,4H-piperazine-N,N `-diium diacetate and its sublimation mechanism: An nonhygroscopic piperazine salt with ionic or cocrystal structure?

• Main Authors: Zaharani, Lia, Johan, Mohd Rafie, Khaligh, Nader Ghaffari
• Format: Article
• Published: Springer 2022
• Subjects: QD Chemistry
• Online Access: http://eprints.um.edu.my/40372/

Thermal phase transitions of 1H,4H-piperazine-N,N `-diium diacetate were investigated by the differential scanning calorimetry (DSC) compared with piperazine and glacial acetic acid. The thermal stability of new sublimable molten salt was determined by thermogravimetric analysis (TGA), and the released gases after decomposition were identified by the thermogravimetric analysis-mass spectrometry (TG-MS). DSC profile of new sublimable organic molten salt was utterly different from those of its reactants, viz. piperazine and glacial acetic acid. Although the probability of reforming the acid and base remains negligible even at high temperatures ( similar to 300 degrees C) for some protic ionic liquids, the thermal behavior results exhibited that this molten salt could sublime at around 145 degrees C in the absence of high or ultrahigh vacuum. A new insight is described for sublimation and recondensation of the molten salt, including transforming the ionic salt in the solid phase into the molecular gas-phase cluster in the vapor phase, and reverse transformation during heating and cooling, respectively. The molten salt is nonhygroscopic contrary to piperazine and glacial acetic acid, which are highly hygroscopic. Furthermore, this work revealed for the first time that certain organic salts containing acceptor-donor hydrogen bonding moieties could be directly sublimed without liquefaction.