Initial Decomposition Pathways of Aqueous Hydroxylamine Solutions

Abstract

This work examined the reaction pathways involved in the initial decomposition of aqueous hydroxylamine solutions via the overall reaction, 2NHOH → NH + HNO + HO, using quantum chemistry calculations incorporating solvent effects. Several possible decomposition mechanisms were identified and investigated: three neutral-neutral bimolecular, two water-catalyzed, one neutral trimolecular, two ion-neutral bimolecular, and one cation-catalyzed. Optimized structures for the reactants, products, and transition states were obtained at the ωB97XD/6-311++G(d,p)/SCRF = (solvent = water) level of theory, and the total electron energies of such structures were calculated at the CBS-QB3 level of theory. The cation-catalyzed reaction 2NHOH + NHOH → NH + HNO + HO + NHOH (maximum energy barrier (ΔE) = 53.6 kJ/mol) and the anion-neutral bimolecular reaction NHOH + NHO → NH + NO + HO (ΔE = 79.0 kJ/mol) were both found to be plausible candidates for the dominant step in the initial decomposition. The results of this study indicate that both acidic and basic conditions can affect the thermal stability of hydroxylamine in water.

Cometabolic biotransformation and microbial-mediated abiotic transformation of sulfonamides by three ammonia oxidizers

“…However, NO and aromatic amines cannot react to form diazonium cations in natural environments. Hydroxylamine is not stable and easy to decompose (2NH 2 OH→NH 3 +HNO+H 2 O) (Izato et al, 2017); it is possible that hydroxylamine reacted with aromatic amines (e.g., SAs) via nitroxyl (HNO) to form diazonium cations. The medium in this study was at pH 8, where the diazonium cation disintegrates via the cleavage of elementary nitrogen and substitutes its diazo-group with a NO 2 -group or OH-group.…”

Decolorization and Mineralization of Rhodamine B in Aqueous Solution with a Triple System of Cerium(IV)/H2O2/Hydroxylamine

“…The observed decrease in RhB degradation with the increase in pH may be attributed to the scavenging of HO • by the increase of HA with increasing pH value. Because the pK a1 value of HA is 5.96, 32 when the pH value is below 5, most of the HA is in its protonated form (H 3 NOH + ), whereas at a pH value in the range of 6.0−14.0, it is mainly in its unprotonated form (H 2 NOH). It has been reported that the reaction rate between HO • with H 2 NOH is Notably, the observed phenomena when the concentration of Ce(IV), H 2 O 2 , and HA exceeds the optimal dosage may be attributed to the excess reagents competing with RhB to consume HO • free radicals.…”

Role of Ammonia Oxidation in Organic Micropollutant Transformation during Wastewater Treatment: Insights from Molecular, Cellular, and Community Level Observations

“…NO/HNO reacts with primary aromatic amines (the antimicrobial active moieties of sulfonamide antibiotics) to form a diazonium cation, which then disintegrates under cleavage of elementary nitrogen and substitutes its diazo-group with a -NO2, -H or -OH (Figure 2I, SI Table S4) 54,80,94 .…”

“…NH 2 OH is highly reactive and potentially toxic with a high turnover and is typically detected at low concentrations (e.g., 0.003–0.031 mg N/L in AOB pure cultures , and 0.03–0.11 mg N/L in lab-scale partial nitritation reactors − ). As a nucleophilic reducing agent, NH 2 OH can undergo decomposition (2NH 2 OH → NH 3 + HNO + H 2 O) or oxidation by O 2 (2NH 2 OH + 1.5O 2 → 2NO + 3H 2 O) to form highly reactive oxidizing intermediates, such as HNO or NO that can chemically transform OMPs . In abiotic transformation tests, the addition of NH 2 OH (ca.…”

“…The mechanism proposed for the reaction between NH 2 OH and sulfonamide OMPs (i.e., sulfonamide antibiotics and asulam) is similar to the abiotic transformations mediated by HNO 2 : NO/HNO reacts with primary aromatic amines (the antimicrobial active moieties of sulfonamide antibiotics) to form a diazonium cation, which then disintegrates under cleavage of elementary nitrogen and substitutes its diazo group with −NO 2 , −H, or −OH (Figure 2I, SI Table S4). 54,80,94 NO. NO is usually detected at very low concentrations in BNR reactors.…”