Hexamethylenetetramine or methenamine is a heterocyclic organic compound with the formula C6H12N4. This white crystalline compound is highly soluble in water and polar organic solvents. It has a cage-like structure similar to adamantane. It is useful in the synthesis of other chemical compounds, e.g., plastics, pharmaceuticals, rubber additives. It sublimes in vacuum at 280 °C. Hexamethylenetetramine is prepared industrially by reacting formaldehyde and ammonia. The reaction can be conducted in gas phase and in solution.