Nitrogen dioxide equilibrium with

Tautomeric equilibrium in amino-substituted 1,2,6-thiadiazine 1,1-dioxides fused with five- or six-membered nitrogen heterocycles has been extensively studied by Goya and colleagues. No amino group participation in tautomeric equilibria in these systems has been observed. 

Table 21.22 Saturated solubilities of atmospheric gases in sea-water at various temperatures Concentrations of oxygen, nitrogen and carbon dioxide in equilibrium with 1 atm (lOI 325 N m ) of designated gas...

By using different membranes, it is possible to obtain potentiometric sensors for gases such as sulfur dioxide or nitrogen dioxide. Such sensors employ similar (acid-base) or other equilibrium processes. These devices, along with their equilibrium processes and internal electrodes, are summarized in Table 6-2. Membrane coverage... 

The carbon dioxide gas dissolved in a sample of water in a partly filled, sealed container has reached equilibrium with its partial pressure in the air above the solution. Explain what happens to the solubility of the CO, if (a) the partial pressure of the CO, gas is doubled by the addition of more CO, (b) the total pressure of the gas above the liquid is doubled by the addition of nitrogen. 

Nitrogen dioxide, N02 (oxidation number -t-4), is a choking, poisonous, brown gas that contributes to the color and odor of smog. The molecule has an odd number of electrons, and in the gas phase it exists in equilibrium with its colorless dimer N204. Only the dimer exists in the solid, and so the brown gas condenses to a colorless solid. When it dissolves in water, NOz disproportionates into nitric acid (oxidation number +5) and nitrogen oxide (oxidation number +2) ... 

The detailed chemistry describing the synthesis of ammonia Is complex, so we Introduce the principles of equilibrium using the chemistry of nitrogen dioxide. Molecules In a sample of nitrogen dioxide are always colliding with one another. As described in Chapter 15, a collision in the correct orientation can result In bond formation, producing an N2 O4 molecule 2 NO2 N2 O4... 

The tetroxide, which forms an equilibrium with nitrogen dioxide, is a very strong oxidant and an endothermic compound. To analyse all the dangerous reactions of... 

Nitrogen dioxide forms an equilibrium with dinitrogen tetroxide. When it is cold, the equilibrium favours the second compound. Depending on the thermal conditions, the dangerous reactions will involve one or the other of these two compounds. Their endothermic character makes them hardly stable. 

The organic substrates in Chart 8 can be divided into two main categories in which (i) the oxidation of olefins, sulfides, and selenides involves oxygen atom transfer to yield epoxides, sulfoxides, and selenoxides, respectively, whereas (ii) the oxidation of hydroquinones and quinone dioximes formally involves loss of two electrons and two protons to yield quinones and dinitrosobenzenes, respectively. In order to provide a unifying mechanistic theme for the seemingly disparate transformations in Chart 8, we note that nitrogen dioxide exists in equilibrium with its dimeric forms, namely, the predominant N—N bonded dimer 02N—N02 and the minor N—O bonded isomer ONO—N02 (equation 88). 

Nitrogen dioxide is a stable radical with an unpaired electron and forms the dimer N204 in the equilibrium reaction ... 

This equilibrium reaction occurs with enthalpy A//=-58.2kJ mol-1 and entropy A S = — 177 J mol-1 K [167], Nitrogen dioxide decays at elevated temperatures in the gas phase by the reaction... 

FIGURE 9.23 Adiabatic flame temperature for stoichiometric combustion of methane in mixtures of oxygen with nitrogen and oxygen with carbon dioxide, computed using NASA s Chemical Equilibrium Analysis (CEA) program [52]. 

Nitrogen dioxide readily converts to other forms of nitrogen oxides. It coexists in equilibrium with its dimeric form, N2O4. The latter is more stable at ordinary temperatures. 

The whole apparatus is baked as efficiently as possible without evaporating large quantities of the manometric fluid or test substance, and is finally sealed off. The apparatus is returned to the vertical position and wholly immersed in a thermostatic bath. The level of the manometer liquid should be exactly equai under these conditions. The apparatus is then arranged as shown in the sketch with bulb B in solid carbon dioxide or liquid nitrogen. When equilibrium is attained the difference of level in the manometer limbs is observed with a cathetometer. The thermostat temperature is readjusted and the process repeated. ... 

Once cooled, the effluent from the process separates into a liquid-water phase and a gaseous phase, the latter containing mainly carbon dioxide along with oxygen which was in excess of the stoichiometric requirements, and nitrogen. The separation is carried out in multiple stages in order to minimize erosion of valves, as well as to maximise the separation due to phase-equilibrium constraints. 

In addition, there is an independent N02-catalyzed reaction, which only becomes important at elevated temperatures and when nitrogen dioxide is a major constituent. It operates by conversion of asyw-ONOO to jyw-N03 therefore, it interferes with the equilibrium ii.-n- Oxidation would then consist of reaction (11A) followed by reactions (42) and (5S)... 

Isolated examples of oxidation at nitrogen have been reported for these systems. They do not form the N-oxides typical of aromatic nitrogen heterocycles, but behave similarly to amines. Thus the 1,2,5-oxadiazine (80) is rapidly oxidized by lead dioxide to the radical (81) (73JA1677), which is in equilibrium with the four-membered ring radical (82). 

Nitrogen dioxide molecules react with NO to form N203, in an equilibrium mixture. The equilibrium mixture of NO> and N204 also reacts with water... 

Nitrogen dioxide rapidly forms an equilibrium mixture with its dimer, dinitrogen tetroxide or nitrogen peroxide [see Eq. (9.11)]. The formation of the tetroxide is favored by low temperature and high pressure104. 

Other observations of the reaction of hydrazine and nitrogen tetroxide substantiate the production of non-equilibrium combustion products. Non-equilibrium product concentrations were found in combustion gases extracted from a small rocket combustion chamber through a molecular beam sampling device with direct mass spec-trometric analysis (31) (39). Under oxidizer rich conditions excessive amounts of nitric oxide were found under fuel rich conditions excessive amounts of ammonia were found. A correlation between the experimentally observed characteristic velocity and nitric oxide concentration exists (40). Related kinetic effects are postulated to account for the two stage flame observed in the burning of hydrazine droplets in nitrogen dioxide atmospheres (41) (42). 

On the basis of the observation that the addition of nitrogen dioxide to compounds with double bonds yields not only nitro compounds, but nitrous acid esters as well (p. 99). Schaarschmidt [38a,39,40] expressed the view that nitrogen dioxide exists in three forms which are in equilibrium. This may be represented in modem symbols in the following way ... 

---