Reactions of NO

Because of the rapid photolysis of NO, during the day (see Chapter 4.G), competing reactions of NO, are important primarily at night. Some of the most important dark reactions are discussed in the following sections. For detailed treatments of nitrate radical chemistry, the reader should consult the extensive reviews by Wayne et al. (1991) and Atkinson (1991). 

One of the most important reactions of NO, is that with N02 to form N205, discussed earlier. This is the only known source of N205 in the atmosphere, and because NO, is only present at significant concentrations at night due to its rapid photolysis, the formation of N2Os is restricted to the dark. 

also reacts quite rapidly with NO, however, and this appears to limit its lifetime in air under many circumstances. The reaction is fast, /c,5 = 2.6 X 10 11 cm3 molecule-1 s-1 at 298 K (DeMore et al., 1997)  

For example, with NO at 1 ppb, the lifetime of NO, with respect to this reaction can be calculated from tN(F = l//c [NO] to be only 2 s. As a result, NO and NO, do not coexist with both at high concentrations, as is the case for NO and O, and for the same reason. 

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Tetraneopentyltitanium and ((CH2)2SiCH2)4Ti [33948-28-6] react with nitric oxide to yield compounds having R groups bonded ia two different ways, as shown by nmr (214). The reactions of NO with R TiCl and R2TiCl2 yield similar products that have Cl iastead of the —ONRNO substituent. 

The principal method used for measuring NO2 is also based on chemiluminescence (Fig. 14-3) (5). NO2 concentrations are determined indirectly from the difference between the NO and NO (NO -I- NO2) concentrations in the atmosphere. These concentrations are determined by measuring the tight emitted from the chemiluminescent reaction of NO with 03 (similar to the reaction of O3 with ethylene noted for the measurement of O3), except that O3 is supplied at a high constant concentration, and the light output is proportional to the concentration of NO present in the ambient air stream. 

Fig. 14-3. NOj chemiluminescent detection principle based on the reaction of NO with O3.

Nitric oxide may induce deleterious effects when airway epithelial or immunological cells are exposed to mineral particles (asbestos, quartz). These particles also stimulate cells to produce NO in large quantities, but pulmonary cells are unable to destroy these particles, and a non-physiologically excess production of NO results, perhaps causing tissue damage due to a reaction of NO with cellular macromolecules. 

The catalytic reaction of NO and CO on single crystal substrates, under ultra-high vacuum conditions, has been extensively studied. Neglecting N2O formation and CO desorption, the Langmuir-Hinshelwood mechanism of the NO + CO reaction can be described by the following sequence of steps [16,17] ... 

This S-nitroso group is in equilibrium with other S-nitroso compounds formed by reaction of NO with small-molecule thiols such as free cysteine or glutathione (an isoglutamylcysteinylglycine tripeptide) ... 

The corresponding nitrites, MNO2, can be prepared by thermal decomposition of MNO3 as indicated above or by reaction of NO with the hydroxide ... 

Many variations on these synthetic routes have been devised and the field is still being actively developed. The reactions of NO coordinated to transition metals have been extensively reviewed. ... 

As already shown in Figure 6.3b the system exhibits remarkable electrophilic promotional behaviour with p values up to 20.64 This is also shown in Fig. 8.60 which depicts a galvanostatic transient. Application of a negative current between the Pt catalyst-working electrode and the Au counter electrode causes a sharp increase in all reaction rates. In the new steady state of the catalyst (achieved within lhr of current application) the catalytic rate increase of C02 and N2 production is about 700%, while lesser enhancement (250-400%) is observed in the rates of CO and N20 production. The appearance of rate maxima immediately after current application can be attributed to the reaction of NO with previously deposited carbon.64... 

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%. 

C15-0003. The following mechanism has been proposed for the reaction of NO with H2 ... 

A reaction of ozone provides an example of concentration effects. Ozone in the atmosphere near the Earth s surface is a serious pollutant that damages soft tissues such as the lungs. In major urban areas, smog alerts are issued whenever there are elevated concentrations of ozone in the lower atmosphere. Nitmgen oxide, another component of photochemical smog, is a colorless gas produced in a side reaction in automobile engines. One reaction that links these species is the reaction of NO and O3 to produce O2 and NO2 ... 

First, analyze the one-step mechanism CO -I- NO2 CO2 4-NO This process is analogous to the reaction of NO and O3 discussed in Section 15-1. In a simple one-step atom transfer, the reaction is first order in each of the starting materials and second order overall ... 

C15-0045. The reaction of NO with CI2 is 2 NO + CI2 2 NOCl Use reactant molecules to write appropriate elementary reactions that satisfy the following criteria (a) a unimolecular decomposition that generates Cl (b) a bimolecular collision in which a Cl atom is transferred between reactants and (c) a termolecular collision leading to the observed products. 

C15-0080. The reaction of NO with O2 to give NO2 is an important process in the formation of smog in Los Angeles 2 NO + O2 2 NO2 Experiments show that this reaction is third order overall. 

Figure 10.8. Temperature-programmed reaction of NO and CO on two surfaces of rhodium. The initially molecularly adsorbed NO dissociates entirely at relatively low temperatures, but NO does not desorb. Note the difference in selectivity and reactivity between the surfaces on Rh(lOO) most of the CO oxidizes to CO2 and the reaction already...

The sudden consumption of the remaining UDMH, and the increased relative importance of N-nitrosamine formation at -30 minutes into the photolysis can be rationalized by assuming that at that time the [NO I/ENO] ratio, and thus the photostationary state [O3], has become sufficiently high that O3 may be reacting with the hydrazine directly, and that reaction (3) begins to dominate over reaction (10). This results in higher rates of UDMH consumption by the OH radicals formed in the UDMH + O3 reaction (1), and by the OH radicals generated by the reaction of NO... 

It is significant that in the absence of O2 (solid points in Figure 4) almost no radicals were formed the amount reported is close to the detection limit of the instrument. In one sense, this observation provides an explanation for the positive effect that O, has on the rate of reaction between NO and CH4 [3,4] i.c., O2 enhances CH,- radical formation. However, the results also indicate that NO itself is not very effective in generating active sites which are responsible for CH,- radical production. This means that the reaction of NO with CH4, in the absence of added O, may occur via a nonradical pathway. 

The values of the rate constants are estimated by fitting equations 1.4a and 1.4b to the concentration versus time data. It should be noted that there are kinetic models that are more complex and integration of the rate equations can only be done numerically. We shall see such models in Chapter 6. An example is given next. Consider the gas phase reaction of NO with 02 (Bellman et al. 1967) ... 

Bellman et al. (1967) have considered the estimation of the two rate constants k and k2 in the Bodenstein-Linder model for the homogeneous gas phase reaction of NO with 02 ... 

Table 6.1 Data for the Homogeneous Gas Phase Reaction of NO with 02.

A different picture emerged from the comparison of IR measurements in static and flow conditions. The IR spectra recorded in the temperature range of 423-823 K during the catalytic reaction of NO with the CuZSM-5 are collected in Figure 2.24. The spectra are dominated by the broad and intense absorption bands centered at 1470, 1630 and 2224 cm-1, assigned to N02-related species such as surface nitrates N03 [77,78],... 

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