Nitrous oxide secondary reactions

Ionizing radiation decomposes gaseous nitrous oxide131-136 into N2, 02, and nitrogen oxides by a series of secondary reactions following primary formation of N20 and N20+. The secondary processes include reactions of neutral fragments and of ionic species and are of considerable complexity. The former are similar to those which occur in the photolytic decomposition. Reactions of ionic species131-136 will not be discussed in this article. 

Recently [35a] it has been found that, contrary to common belief, tertiary aliphatic amines react with aqueous nitrous acid to undergo dealkylation to form a carbonyl compound, a secondary nitrosoamine, and nitrous oxide. Base-weakening groups markedly reduce nitrosative cleavage, and quaterniza-tion prevents it completely. Several examples of this reaction are shown in Table II. 

In addition to the three main types of reaction involved in nitrocellulose decomposition, the author assumes that secondary reactions also occur originating in the chemical combination between oxides of nitrogen and water vapour to produce nitric and nitrous acids, which in turn react with the nitrocellulose. By heating nitrocotton with dilute nitric acid at 40°C, Desmaroux found in this instance that hydrolytic and oxidation reactions predominate, causing a weight loss of +-J of the total loss (see Table 67). 

The production of nitrous oxide is not exactly quantitative because of secondary reactions. A solution of nitroguanidine in concentrated sulfuric acid, after standing for some time, no longer gives a precipitate of nitroguanidine when it is diluted with water. 

Nitroxyl forms nitrous oxide, and the secondary amine reacts with more nitrous acid giving the nitrosamine. Based on the observed isotope effect, the rate-determining step was thought to be the loss of HNO. Nitrous oxide is believed to arise from elimination of nitroxyl in many other reactions. 

Nitrourea is decomposed quantitatively into cyanic acid and nitrous oxide when heated in aqueous solution. If primary or secondary amines are present, the products are alkylureas or N,N-diaIkylureas, respectively.Alcohol is used as a solvent for amines which are only slightly soluble In water. The yields in general are excellent (70-98%), and the reaction is preferred to the exchange with urea described above. Alkanolamines give hydroxyalkylureas in 85-95% yields." Nitrourea is conveniently prepared in 90% yield from urea nitrate."... 

The overall reaction is energy yielding, and allows sufficient ATP production to support reverse electron transport for CO2 fixation. However, the first step, oxidation of NH3 to hydroxylamine, requires the input of reducing power. The second step, hydroxylamine oxidation, yields four electrons. These join the electron transport chain at the level of ubiquinone, from which two are shunted back to AMO for activation of NH3. The N oxidation and electron transport pathways in Nitrosomonas are linked in the cytoplasmic membrane and periplasmic space detailed information from the N. europaea genome (Chain et al., 2003) is consistent with the previous biochemical characterizations of the system (Whittaker et al., 2000). Depending on conditions (and enhanced at low oxygen concentrations), nitric oxide (NO), nitrous oxide (N2O) and even dinitrogen gas (N2) have been reported as secondary products... 

Phenol was the main product over the whole temperature range, butthe formation of byproducts became important above 400°C (Fig. 4). At this temperature the expected exponential increase of phenol yield versus temperature did not occur because consecutive reactions of phenol lead to the formation of di-hydroxy-benzenes (catechol, resorcinol) and benzoquinone as well as by total oxidation. Surprisingly, no hydroquinone was found, suggesting a fast eonsecutive oxidation of the para-isomer to benzoquinone [5-7]. Additionally, above 400°C the conversion of nitrous oxide increased because secondary products generated by these further reactions need higher stoichiometric amounts of nitrous oxide (e.g. total oxidation requires 15 molecules of nitrous oxide) [6]. The increase in undesired products, especially the steep rise of total oxidation, confined the maximum operating temperature to 400°C. 

Following the original work of Scholes and Simic, many workers have studied the production of N2 from nitrous oxide solutions. It is now generally agreed that the results cannot be interpreted solely in terms of electron capture. Because of this and because of the general interest in this system, this solute is treated in a separate section after the concentration dependence of secondary ionic reactions is discussed. 

Properties and reactions of nitramines Secondary nitramines are neutral, primary nitramines form salts with bases, but an excess of alkali often causes decomposition to the carbonyl compound, nitrogen, and water. Secondary nitramines and aqueous alkali afford nitrous acid, aldehyde, and primary amine. Acids decompose primary aliphatic nitramines with formation of nitrous oxide in a reaction that has not yet been clarified thus these compounds cannot be hydrolysed by acid to amines in the same way as nitrosamines, although, like the latter, they can be reduced to hydrazines. Primary and secondary aromatic nitramines readily rearrange to C-nitroarylamines in acid solution. Most nitramines decompose explosively when heated, but the lower aliphatic secondary nitramines can be distilled in a vacuum. 

The previous section of fhis chapter has described the flame parameters that must be controlled and optimized to produce a polymer film of the desired level of wettability. The present section is a review of the current state of knowledge of the chemical kinetic mechanism of the reactions between flame reactants and the surface layer of polymer molecules. The discussion begins with a consideration of the flow, impingement, and quenching of the combustion products and reactive intermediates on the cooled surface of the polymer film. The discussion then proceeds to describe a detailed chemical kinetic mechanism for the surface reaction. The resulting mechanism is able to qualitatively account for the influence of the major flame variables on the wettability of fhe polymer surface. Finally, the addition of secondary species, specifically nitrous oxide (N2O), to the primary reactants to alter the thermal and/or chemical behavior of fhe flame is discussed, providing an example of fhe effecfs of flame-chemistry modification. 

Both turbulent burners and premix burners have been used for atomic fluorescence. The premix burner is usually round in shape (a modification of the Meker-type burner), since this provides better geometry for fluorescence than does a slot burner. For an optimum detection limit, the premix burner is also shielded that is, an inert gas such as argon or nitrogen is directed in a sheath around the flame. This elongates the interconal zone and lifts the secondary reaction zone above the burner, separating it from the lower part of the interconal zone where the excitation beam passes. The result is less background emission and less noise, particularly in hydrocarbon flames like air-acetylene or nitrous oxide-acetylene. The premix burner, especially when shielded, appears to offer increased sensitivity over the turbulent burner. 

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