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Published on: September 9, 2016
Initial Decomposition Pathways of Aqueous Hydroxylamine Solutions
Yu-Ichiro Izato1, Mitsuo Koshi1, Atsumi Miyake1
1Institute of Advanced Sciences, Yokohama National University , 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
The Journal of Physical Chemistry. B
|April 4, 2017
Summary
Quantum chemistry calculations reveal that both cation-catalyzed and anion-neutral reactions are key pathways for hydroxylamine decomposition in water, influencing its thermal stability under varying pH conditions.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Chemical Kinetics
Background:
- Hydroxylamine (NH2OH) decomposition in aqueous solutions is a critical process with implications for chemical stability and safety.
- Understanding the reaction mechanisms is essential for predicting and controlling hydroxylamine's behavior.
Purpose of the Study:
- To investigate the initial decomposition pathways of aqueous hydroxylamine using theoretical calculations.
- To identify the dominant reaction mechanisms and their energy barriers.
- To assess the influence of pH conditions on hydroxylamine's thermal stability.
Main Methods:
- Quantum chemistry calculations were employed, incorporating solvent effects for aqueous solutions.
- Density functional theory (ωB97XD/6-311++G(d,p)/SCRF) was used for structure optimization.
- Coupled cluster theory (CBS-QB3) was utilized for accurate energy calculations.
Main Results:
- Several decomposition mechanisms were explored, including neutral-neutral, water-catalyzed, trimolecular, ion-neutral, and cation-catalyzed pathways.
- The cation-catalyzed reaction (2NH2OH + NH3OH+ → NH4+ + HNO + H2O + NH2OH) has a low energy barrier (ΔE0‡ = 53.6 kJ/mol).
- The anion-neutral bimolecular reaction (NH2OH + NH2O- → NH3 + 1NO- + H2O) also presents a plausible dominant step (ΔE0‡ = 79.0 kJ/mol).
Conclusions:
- Both acidic (cation-catalyzed) and basic (anion-neutral) conditions significantly impact the initial decomposition rates of hydroxylamine.
- The identified pathways provide crucial insights into the thermal stability of aqueous hydroxylamine solutions.
- Theoretical calculations offer a robust method for elucidating complex reaction mechanisms in solution.
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