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

Abstract

Rate constants for the nitrate ( • NO 3 ) 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 • NO 3 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 NO 3 − anion and corresponding tropylium cation produced by the • NO 3 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.

Radiolytic Evaluation of 3,4,3-LI(1,2-HOPO) in Aqueous Solutions

“…A transient adduct spectrum was also recorded for the NO 3 • radical adduct of HOPO, as shown in SI Figure S12. The HOPO reaction kinetics with the NO 3 • radical, shown in Figures S5 and S10 and Table , are slower than those with the • OH radical, which is consistent with their typical trends in reaction behavior. , However, the rate coefficients for the NO 3 • radical reaction with HOPO and its [Nd III (HOPO)] − complex are still sufficiently fast for this degradation pathway to be significant under UNF reprocessing scenario conditions (Table ). As with the H • atom and the • OH radical, the reaction of the NO 3 • radical with HOPO and its [Nd III (HOPO)] − complex was unaffected by Nd(III) complexation and believed to again proceed via addition to HOPO’s hydroxypyridinone rings: HOPO / false[ Nd III ( HOPO ) false] − + NO 3 • → HOPO false( prefix+ NO 3 false) • / false[ Nd III false( HOPO ( + NO 3 ) false) • false] − …”

Reactivity of Undissociated Molecular Nitric Acid at the Air–Water Interface

“…In principle, reactions (1) and () can also occur in bulk solution, but their contribution to renoxification is expected to be less important than for interfacial chemistry. The concentrations of undissociated nitric acid and OH are much lower in that case, and the small amounts of the formed nitrate radicals, not likely to escape to the air, should react quickly in the aqueous phase before wet deposition.…”

Nitrate-Mediated Alcohol Oxidation on Cadmium Sulfide Photocatalysts

“…One particularly promising mediator class that may have applications in photocatalysis is nitrate salts. Previous electrochemical work has demonstrated nitrate-mediated alcohol oxidations on carbon and platinum electrodes. − In addition to electrochemical mediation, the nitrate ion/nitrate radical couple (NO 3 – /NO 3 • ) is involved in atmospheric volatile organic compound oxidations. , This reactivity toward organic compounds has also been applied to solution oxidations, where nitrate radical generation occurs by laser flash photolysis or radiolysis of dissolved nitrate salts. − In addition to these generation methods, photochemical nitrate radical formation is possible by TiO 2 in aqueous nitrate solutions . Despite these promising characteristics, alcohol oxidation mediated by nitrate has been limited to gas phase TiO 2 applications and homogeneous oxidations on organic dyes .…”