Nitrogen nitrite/nitrate addition

The study of the biosynthesis of inorganic nitrogen oxides has a long and distinguished history, principally in the field of microbial and plant nitrogen metabolism (Zumft, 1993). Relatively recently, it has been found that NO, in addition to other species such as nitrite, nitrate, and NjO, is a true intermediate in the biological nitrogen cycle, as described in detail in Chapter 9. 

A number of inorganic species also absorb. We have noted that many ions of the transition metals are colored in solution and can thus be determined by spectrophotometric measurement. In addition, a number of other species show characteristic absorption peaks, including nitrite, nitrate, and chromate ions, the oxides of nitrogen, the elemental halogens, and ozone. 

At room temperature, Htde reaction occurs between carbon dioxide and sodium, but burning sodium reacts vigorously. Under controUed conditions, sodium formate or oxalate may be obtained (8,16). On impact, sodium is reported to react explosively with soHd carbon dioxide. In addition to the carbide-forrning reaction, carbon monoxide reacts with sodium at 250—340°C to yield sodium carbonyl, (NaCO) (39,40). Above 1100°C, the temperature of the DeviHe process, carbon monoxide and sodium do not react. Sodium reacts with nitrous oxide to form sodium oxide and bums in nitric oxide to form a mixture of nitrite and hyponitrite. At low temperature, Hquid nitrogen pentoxide reacts with sodium to produce nitrogen dioxide and sodium nitrate. 

An attempt to combine electrochemical and micellar-catalytic methods is interesting from the point of view of the mechanism of anode nitration of 1,4-dimethoxybenzene with sodinm nitrite (Laurent et al. 1984). The reaction was performed in a mixture of water in the presence of 2% surface-active compounds of cationic, anionic, or neutral nature. It was established that 1,4-dimethoxy-2-nitrobenzene (the product) was formed only in the region of potentials corresponding to simultaneous electrooxidation of the substrate to the cation-radical and the nitrite ion to the nitrogen dioxide radical (1.5 V versus saturated calomel electrode). At potentials of oxidation of the sole nitrite ion (0.8 V), no nitration was observed. Consequently, radical substitution in the neutral substrate does not take place. Two feasible mechanisms remain for addition to the cation-radical form, as follows ... 

Nitrite reductases (NiRs)—enzymes found in several strains of denitrifying bacteria— catalyze the one-electron reduction of nitrite anion to nitric oxide (Equation 1). - In addition to the importance of this process in the global nitrogen cycle (Figure 1), further incentive for the study of the denitrification process is provided by its environmental impact, ranging from the production of NO as a pollutant and NjO as a potent greenhouse gas, to lake eutrophication due to farm runoff that contains high concentrations of nitrates and nitrites. 

The capability of NO to reduce nitrates, providing a pathway for the production of ammonium nitrite and thus of nitrogen, has also been demonstrated recently by Weitz and co-workers, mainly on the basis of IR data collected over BaNa-Y zeolite [75] however, according to a parallel additional route NO would also react with NO2 to form N2O3 and then nitrogen [reactions (13.25) and (13.26)], as already discussed. The oxidation of NO by surface nitrates over a Pt-Ba/Al2O3 catalyst has also been reported by Olsson et al. [76], whereas the formation of surface nitrates from NO2 on bare AI2O3 has been reported by Apostolescu et al. [77] and previously observed in our laboratories also [78]. 

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