Kinetic and mechanistic aspects of the NO oxidation by O2 in aqueous phase |
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Authors: | Mar lal Pires,Michel J. Rossi,David S. Ross |
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Affiliation: | Marçlal Pires,Michel J. Rossi,David S. Ross |
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Abstract: | The oxidation kinetics of NO by O2 in aqueous solution was observed using a stopped flow apparatus. The kinetics follows a third order rate law of the form k · [NO]2 · [O2] in analogy to gas-phase results. The rate constant at 296 K was measured as (6.4 ± 0.8) · 106 M?2 s?1 with an activation energy of 2.3 kcal/mol and a preexponential factor of (4.0 ± 0.5) · 108 M?2 s?1. The rate constant displays a very slight pH dependence corresponding to less than a factor of three over the range 0 to 12. The system NO/O2 in aqueous solution is an efficient nitrosating agent which has been tested using phenol as a substrate over the pH range 0 to 12. The rate limiting step leading to formation of 4-nitrosophenol is the formation of the reactive intermediate whose competitive hydrolysis yields HONO or NO2?. The absence of NO3? in the autoxidation of NO, the exclusive presence of NO2? as a product of the nitrosation reaction of phenol, and the kinetic results of the N3? trapping experiments point towards N2O3 as the reactive intermediate. © 1994 John Wiley & Sons, Inc. |
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