Protonation of Nitramines: Where Does the Proton Go?

Abstract The reactions of nitramine, N ‐methyl nitramine, and N , N ‐dimethyl nitramine with anhydrous HF and the superacids HF/MF 5 (M=As, Sb) were investigated at temperatures below −40 °C. In solution, exclusive O‐protonation was observed by multinuclear NMR spectroscopy. Whereas no solid product could be isolated from the neat HF solutions even at −78 °C, in the HF/MF 5 systems, protonated nitramine MF 6 − salts were isolated for the first time as moisture‐sensitive solids that decompose at temperatures above −40 °C. In the solid state, depending on the counterion, O‐protonated or N‐protonated cations can be formed, in accord with theoretical calculations which show that the energy differences between O‐protonation and N‐protonation are very small. The salts [H 2 N‐NO 2 H][AsF 6 ], [H 3 N‐NO 2 ][SbF 6 ], [MeHNNO 2 H][SbF 6 ], and [Me 2 NNO 2 H][SbF 6 ] were characterized by their X‐ray crystal structures.