Mechanisms of Acid-Promoted N and NO Generation from NHNO and NHNO.

The effects of water, formic acid, and nitric acid on N and NO generation from NHNO and NHNO are studied using high-level quantum-chemical calculations. It is shown that the reaction barriers from isolated NHNO and NHNO are 35.5 and 38.1 kcal/mol, respectively. When the NHNO and NHNO reactions are examined in the presence of water, formic acid, or nitric acid, the energy barriers are different. The mechanisms of these reactions are revealed through reaction pathway calculations. The isomerization of intermediate HNNOH and HNNOOH molecules, which follows a group rotation mechanism, plays a key role in reactions of isolated NHNO and NHNO. However, the presence of water, formic acid, or nitric acid changes the isomerization mechanism substantially. HNNOH or HNNOOH and the catalyzing molecule form a doubly hydrogen-bonded prereactive complex, which, in turn, facilities hydrogen atom migration (this is denoted as the hydrogen atom migration mechanism). This study demonstrates the feasibility of N or NO generation from NHNO and NHNO in the presence of water, formic acid, or nitric acid.