Nitrate/nitrous acid equilibrium

A kinetic study of nitrous acid-catalyzed nitration of naphthalene with an excess of nitric acid in aqueous mixture of sulfuric and acetic acids (Leis et al. 1988) shows a transition from first-order to second-order kinetics with respect to naphthalene. (At this acidity, the rate of reaction through the nitronium ion is too slow to be significant the amount of nitrous acid is sufficient to make one-electron oxidation of naphthalene as the main reaction path.) The reaction that initially had the first-order in respect to naphthalene becomes the second-order reaction. The electron transfer from naphthalene to NO+ has an equilibrium (reversible) character. In excess of the substrate, the equilibrium shifts to the right. A cause of the shift is the stabilization of cation-radical by uncharged naphthalene. The stabilized cation-radical dimer (NaphH)2 is just involved in nitration ... 

Mechanistic studies of A-nitrosation in aqueous solutions are complicated, however, by the existence of several nitrous species in equilibrium with molecular nitrous acid, many of which are effective nitrosating reagents (a situation similar to that for aromatic nitration) Some of the reagents formed in aqueous solution are listed below in order of increasing activity. In the presence of basic... 

Oxidized nitrogen forms anions nitrous and nitric acids, i.e., nitrates NOj and nitrites NO2. As diagram Eh vs. pH shows, the nitrate form of nitrogen is positioned along the upper limit of H O stability. The equilibrium between aquaphilic NOj and may be evaluated from a reaction ... 

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