Reaction of NO with Oxygen

The reaction of NO with O2 in the gas phase results in the formation of nitrogen dioxide (NO2). The kinetics of this reaction are second order in NO and first order in O2 (see, e.g., Olbregts, 1985). Consistent with the kinetics, the following reactions have been proposed  

An elementary termolecular process has been proposed as well (however, debating these mechanistic issues is beyond the scope of this chapter). 

the rate equation indicates that the decomposition of NO in air is not linear with respect to concentration. Hence, high concentrations of NO will degrade rapidly, and as lower concentrations are reached the rate of loss will decline. For example, a 10,000-ppm concentration of NO in air will be half gone in only 24 sec, whereas a 10-ppm mixture will be half gone in 7 hr. (Note that the often used term half-life is inappropriate since the decay is not first order ) In the gas phase NO2 is the terminal product. In aqueous solution, NO2 decomposes to give equal amounts of nitrite, NO2, and nitrate, NOl [due to reactions (6) and (7)]. 

since reaction (6) is second order in NO2, and NO2 levels will be kept low by reaction (8), which is fast (assuming that NO concentrations are generally higher than NO2 concentrations), the rate of reaction (6) is low and reactions (8) and (9) predominate. 

Based on reactions (l)-(9), it begins to become obvious that the chemistry of NO in aqueous aerobic systems is complex. That is, considering only these nine reactions (and not taking into account any redox reactions with biological components), possibly seven nitrogen oxide species can exist in solution simultaneously [NO, -OONO, NO2, (NO)2, N2O3, NO2, and NOi[. Since O2 is the ultimate oxidant in the formation of the oxidized NO species in aqueous solutions, under anaerobic conditions NO should be stable indefinitely (at least in the absence of any other redox factors). Indeed, if made up properly, degassed solutions of NO can last for months (Feelisch, 1991). 

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Alternatively, NO2 radical is produced in the body by the reaction of NO with oxygen [Eq. (10)] and also by peroxidase-catalyzed oxidation of nitrite salts. ... 

The reactions of NO with oxygen and nitrogen ions Ferguson et They studied the reactions have been reported by... 

Fig. 13. Interplay of ROS and RNS in physiology and pathology. When produced at steady-state levels, superoxide is efficiently removed by SODs. Under these conditions, NO reacts mainly hy activating soluble guanylate cyclase to produce cGMP and/or to induce posttransla-tional modification of protein by forming S-nitrosothiols. However, in different pathologies, when one or both of the molecules are overproduced or/and SOD levels reduced, NO and 02 combine to give peroxynitrite, a powerful oxidant. Perox3mitrite can react directly with the biomolecules or can homolytically decompose to give OH and NO2 radicals, both of which can additionally he formed in the reaction of superoxide with free metal ions and in reaction of NO with oxygen, respectively.

The mechanism postulates the formation of nitrous acid (HNO2) and nitric acid (HNO3) by the reaction of NO with oxygen at the cathode under wet conditions. The simultaneous occurrence of the anodic and cathodic steps comprising reactions (5.6) and (5.8) above on the cathode create a mixed potential at the electrode that tends to reduce the cathode potential and retard the oxygen reduction reaction (5.9) [37,38]. The impact of NO contamination is shown in Pigure 5.2 and Eigure 5.3. 

The chemical reaction of NO with oxygen in the air forms NO2, which produces the reddish brown coior of smog. 

The intrinsic kinetics of the reactions taking place in the scrubber, i.e. the reaction of NO with the iron chelate forming an iron nitrosyl complex (eq. 1) and the undesired oxidation reaction of the iron chelate (xanpla (eq. 2) wae deteimined in dedicated stirred cell contactors. Typical process conditions were T = 25-55 °C [Fe"(EDTA) "] = 1-100 mol/m [NO] = 1-1000 ppm pH = 5-8 and an oxygen level ranging between 1 and 20 vol%. 

Neil Spokes and I, in this laboratory (SRI), have studied some of the reactions of radicals with oxygen from 500°K., for the methyl radical, to 1500°K. (7). The technique is the method of very low pressure pyrolysis (VLPP), which has been described recently (6). For methyl radicals we found that there is no measurable reaction over this entire temperature range after 10,000 collisions of methyl with oxygen. From these results, we can assign a lower limit to the activation energy for Reaction 8, of 24 kcal. 

H.16 The first stage in the production of nitric acid by the Ostwald process is the reaction of ammonia with oxygen, producing nitric oxide, NO, and water. The nitric oxide further reacts with oxygen to produce nitrogen dioxide, which, when dissolved in water, produces nitric acid and nitrogen oxide. Write the three balanced equations that lead to the production of nitric acid. 

There have been numerous studies of low-temperature chemical reactions of matrix-isolated reactants (see, for example, the review by Perutz [1985]). Two of the most interesting from the standpoint of this volume are the reactions of NO with 02 and 03 studied by Smith and Guillory [1977] and Lucas and Pimentel [1979]. The cis dimer (NO)2 has been formed in solid oxygen at 13-29 K. Reaction of this species with the 02 matrix forms the product N204 in an electronically excited state. The transition state structure is reportedly of the form... 

Corrosion can also occur by a direct chemical reaction of a metal with its environment such as the formation of a volatile oxide or compounds, the dissolution of metals in fused metal halides. The reaction of molybdenum with oxygen and the reaction of iron or aluminum with chlorine are typical examples of metal/gas chemical reactions. In these reactions, the metal surface stays film-free and there is no transport of electrical charge.1 Fontana and Staehle2 have stated that corrosion should include the reaction of metals, glasses, ionic solids, polymeric solids and composites with environments that embrace liquid metals, gases, aqueous and other nonaqueous solutions. 

The reactions of NO with copper proteins as possible NO targets in vivo are not as well characterized as those with iron proteins. Recent studies indicate, however, that redox reactions can be very fast even at low NO concentrations and in the presence of oxygen, and therefore the reactions may be of physiological relevance. In general, it is assumed that different spectroscopic t5rpes of copper centers react differently with NO (54). 

Although 02 is represented here as the oxidizing agent for NO, the actual oxidizing agent is probably some type of peroxide compound produced by the reaction of oxygen with pollutants. The direct reaction of NO with 02 is very slow. 

Davies and Thrush studied the reaction of oxygen atoms, produced by reaction of NO with N atoms prepared in an electric discharge, with HCN, CICN, and BrCN, and found the rate of O atom consumption to be first-order in O and in XCN. In each case the activation energy found was considerably less than the energy needed to abstract a terminal atom. Furthermore, the O atom consumption was twice the NO produced. This led them to propose the scheme... 

When CO2 is added to the expansion, the clustering of CO2 with NO competes with the dimerization, causing a decrease in the total signal. This reduction of the signal, attributable to NO/CO2 clusters, points to the retarding effect the polyatomic spectator has on the formation of electronically excited NO2. It can be due either to a decrease in the total cross section for reaction or to quenching of the channel that produces the electronically excited product. The same results were obtained when SO 2 was used instead of CO2. A similar effect was observed in the reaction of CO with oxygen, where two CO2 molecules attached to CO dramatically reduced the production of the electronically excited C02. ... 

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