High pressure Raman spectroscopy measurements in a diamond anvil cell (0 - 20 GPa) on HNO3-2-nitropropane mixtures are reported. These mixtures have been chosen as a model propellant, where neither component is explosive by itself The high pressure decomposition of the mixture with oxygen balance (O.B. = 0) has been observed and the recovered products analyzed and identified. The initiation of the chemical decomposition is correlated with he weakening of the N-O bonds in the mixture. The study of a mixture at O.B. = 0 with (HNO3)-N-15 permitted us to determine the origin of the nitrogen formation and to suggest a chemical pathway.