Thermal decomposition of aminotetrazoles

The thermal decomposition of 5-aminotetrazole (5-AT) has been studied by thermogravimetry, thermal volumometry, DSC, DTA and EGA. Solid products of thermal decomposition have been identified by IR spectroscopy and gaseous products by IR and mass spectrometry. Theoretical considerations of thermodynamic characteristics and energies of atomic bonding in the 5-AT tautomeric forms and intermediates have been carried out by the MO SCF method in the MNDO approximation. On the basis of IR and available literature data it is shown that dehydrated 5-AT exists mainly in the imino form in the solid state. Thermal treatment leads to increasing content of the amino form. The thermal decomposition of the imino form of 5-AT starts just after melting and results in hydrogen azide and carbodiimide. The linear polymer of carbodiimide and melamine derivatives have been identified in the solid residue. Further increase of temperature in the course of linear heating leads to another route of thermal decomposition involving the amino form of 5-AT accompanied by the evolution of nitrogen. Apparent activation energies of these routes determined from non-isothermal thermogravimetric data amount to 165 and 135 kJ mol−1, respectively.