The Reactivity of the Nitrate Radical (• NO3 ) in Aqueous and Organic Solutions

Abstract

Rate constants for the nitrate (•NO3) radical reaction with alcohols, alkanes, alkenes, and several aromatic compounds were measured in aqueous and tert-butanol solution for comparison to aqueous and acetonitrile values from the literature. The measured trends provide insight into the reactions of the •NO3 radical in various media. The reaction with alcohols primarily consists of hydrogen-atom abstraction from the alpha-hydroxy position and is faster in solvents of lower polarity where the diffusivity of the radical is greater. Alkenes react faster than alkanes, and their rate constants are also faster in nonpolar solution. The situation is reversed for the nitrate radical reaction with the aromatic compounds, where the rate constants in tert-butanol are slower. This is attributed to the need to solvate the NO3− anion and corresponding tropylium cation produced by the •NO3 radical electron transfer reaction. A linear correlation was found between measured rate constants in water and acetonitrile, which can be used to estimate aqueous nitrate radical rate constants for compounds having low water solubility.