The hydrothermolysis reaction scheme of cyanamide, NH2CN, and dicyandiamide, (NH2)(2)CNCN, applies to the role of these compounds in chemical evolution and to their destruction in aqueous waste streams by hydrothermal methods. Real-time IR spectroscopy with an optically accessible flow cell and Raman spectroscopy with a stopped-flow cell were used at set temperatures of 130-270 degrees C and a pressure of 275 bar to specify the details of the pathway. Rate constants and Arrhenius parameters were determined for the major steps, i.e., hydrolysis of cyanamide, conversion of cyanamide into dicyandiamide, hydrolysis of dicyandiamide, and hydrolysis of the guanylurea intermediate, Previously reported hydrolysis kinetics for guanidine and urea at hydrothermal conditions were used to complete the kinetic scheme. In addition, the apparent equilibrium constants for deprotonation of cyanamide and the protonation of dicyandiamide and its monoanion were determined. The conversion of dicyandiamide to ammeline and the hydrolysis of ammeline were observed by Raman spectroscopy at longer times than were used for the kinetic analysis. A relatively complete and consistent reaction scheme now exists for the cyanamide-dicyandiamide system at hydrothermal conditions.