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Acid-Catalyzed Amine-Borane Reduction of Nitrite
Kevin E. Bell1, Henry C. Kelly
1Department of Chemistry, Texas Christian University, Fort Worth, Texas 76129.
Inorganic Chemistry
|December 4, 1996
Summary
Trimethylamine-borane reduces nitrite in an acid-catalyzed reaction. This study details the reaction kinetics and proposes a mechanism involving protonated nitrous acid and hydride attack, yielding hydrogen and nitrous oxide.
Area of Science:
- Chemical kinetics
- Reaction mechanisms
- Inorganic chemistry
Background:
- Nitrite reduction is crucial in various chemical and environmental processes.
- Understanding the reaction kinetics of nitrite with reducing agents like amine-boranes provides insights into reaction pathways.
Purpose of the Study:
- To elucidate the reaction mechanism for the reduction of nitrite by trimethylamine-borane.
- To determine the kinetic parameters and rate-determining steps of this reaction.
Main Methods:
- Spectrophotometric monitoring of nitrite decrease under pseudo-first-order conditions.
- Kinetic studies across varying pH and acid concentrations.
- Solvent isotope effect and substrate isotope effect measurements.
Main Results:
- The reaction is acid-catalyzed, first-order in both nitrite and trimethylamine-borane.
- Molar equivalence of NaNO(2) to (CH(3))(3)NBH(3) is 2:1, producing equimolar H(2) and N(2)O.
- Observed inverse solvent isotope effect and normal substrate isotope effect.
Conclusions:
- The reaction proceeds via pre-equilibrium protonation of nitrous acid, followed by rate-limiting hydride attack.
- The proposed mechanism involves intermediates like H(2)ONO(+) or NO(+) and nitrosyl hydride.