Phase Transition Analysis of 5-Aminotetrazole from Room Temperature to the Melting Point

Abstract

The phase transition behavior of the 5-aminotetrazole (5-ATZ) crystal was studied in the range of room temperature to the melting point by the differential scanning calorimetry and powder X-ray diffraction techniques to investigate the dehydration phenomenon and to obtain the physical state of the high temperature phase. We found that 5-ATZ has one monohydrate crystal phase and three anhydrous crystal phases (I, II, and III) up to its melting point. The dehydration reaction of the monohydrate crystal occurred at about 50 °C. The dehydration enthalpy was 12.2 kcal/mol. The required activation energy was calculated using the Kissinger method, yielding the value of 27.1 kcal/mol. The phase transitions accompanying the sublimation from phase I to phase II and from phase II to phase III were observed during the prolonged heating at 175 °C. The dehydration phenomenon was also examined through quantum chemical calculations, and the calculated energy to eliminate a water molecule from the monohydrate crystal by the density functional theory at the M06/cc-pVTZ level basically agreed with the experimentally determined dehydration enthalpy.

Quantitative Analysis of Hydration Using Nitrogen-14 Nuclear Quadrupole Resonance

“…Each anhydrous ATZ sample was obtained by drying to a constant mass of ∼12 g ATZMH and then using exactly 8.5 g of the anhydrous ATZ per sample, which corresponds to n ATZ 0 = 100 mmol of material ( M ATZ = 85.068 g/mol). The material was dried in a vacuum oven at 60 °C for 1 h per cycle . In all cases, two cycles were enough to achieve a constant mass.…”

“…The material was dried in a vacuum oven at 60 °C for 1 h per cycle. 17 In all cases, two cycles were enough to achieve a constant mass.…”

Crystal structure of anhydrous 5-aminotetrazole and its high-pressure behavior

“…We performed a MD calculation of 5-ATZ at high temperature and high pressure and observed a variety of changes in the bonding state. The structure analyses for the other two anhydrous phases II and III found at high temperature 13 are still in progress.…”

Periodic DFT Calculations—Review of Applications in the Pharmaceutical Sciences

“…The subject of dehydration is of great importance for the industry and it often relies on the relative humidity and phase purity [94]. Hence, the understanding of the mechanism behind dehydration is of high value for the controlling product quality throughout its processing.…”