A Systematic Study of the Solid-State Pathway from Melamine via Melaminate to Carbodiimide under Evolution of Hydrogen

Thermal analysis techniques, such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), can provide valuable insights into thermal properties, intermediate phases, and phase transitions; sometimes even a whole series of compounds appears in a given system. The solid-state reaction pathway from melamine to carbodiimide, monitored by DSC, involves a sequence of chemical reactions and intermediate phases departing from the reaction of potassium hydride and melamine. The fully analyzed reaction cascade begins with the formation of potassium melaminate, K(C₃N₆H₅), and progresses through several intermediate phases, each with distinct structures and properties, before ultimately yielding β-K₂(CN₂). All crystalline compounds appearing in this reaction sequence are identified using X-ray diffraction analyses. With a 6:1 ratio of potassium hydride and melamine, equal numbers of protic and hydridic hydrogen atoms in the starting materials favor the release of H₂ until the formation of the final product K₂(CN₂), which appears with two modifications.