Solvent and deuterim isotope effects on the decomposition of ammonium nitrite solutions
Journal Article
·
· Journal of Solution Chemistry
The rate of decomposition of HN{sub 4}NO{sub 2} solutions, at pH 5-7, equals K[NH{sub 3}] [HNO{sub 2}]{sup 2} or k[NH{sup =}{sub 4}] [NO{sup -}{sub 2}] [HNO{sub 2}]. A plausible mechanism involves a rate-determining attack of N{sub 2}O{sub 3}, derived from HNO{sub 2} on NH{sub 3}. {Delta}H{double_dagger} and {Delta}S{double_dagger} are 82 KJ-mol{sup -1} and -27 J-mol{sup -1}-K{sup -1}, respectively. On partially replacing the solvent water by methanol or ethanol, the change {Epsilon}{Delta}G{double_dagger}, coupled with the calculated standard Gibbs energy of transfer of the reactants from water to the mixed solvent indicated that, in the latter, there is a greater destabilization of the transition state compared to that of the reactants. This can be explained by assuming two hydrogen bonds from the same water molecule to the transition state and hence a loss of hydrogen bond energy in the mixed solvent compared to the aqueous solution. The rate constant for the reaction of ND{sub 4}NO{sub 2} in D{sub 2}O compared to the reaction of NH{sub 4}HO{sub 2} in water, gave a composite isotope effect involving two acid-base equilibria, suggested in the proposed mechanism; in addition to primary isotope effects in the equilibrium: 2 HNO{sub 2} N{sub 2}O{sub 3} + H{sub 2}O.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 379371
- Journal Information:
- Journal of Solution Chemistry, Journal Name: Journal of Solution Chemistry Journal Issue: 5 Vol. 25; ISSN 0095-9782; ISSN JSLCAG
- Country of Publication:
- United States
- Language:
- English
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