Dimerization nitric oxide-nitrogen dioxide reactions

D. Dimerization Reactions between Nitric Oxide and Nitrogen Dioxide... 

The features of initiation of free radical reactions in polymers by dimers of nitrogen dioxide are considered. The conversion of planar dimers into nitrosyl nitrate in the presence of amide groups of macromolecules has been revealed. Nitrosyl nitrate initiates radical reactions in oxidative primary process of electron transfer with formation of intermediate radical cations and nitric oxide. As a result of subsequent reactions, nitrogen-containing radicals are produced. The dimer conversion has been exhibited by estimation of the oxyaminoxyl radical yield in characteristic reaction of p-benzoquinone with nitrogen dioxide on addition of aromatic polyamide and polyvinylpyrrolidone to reacting system. The isomerisation of planar dimers is efficient in their complexes with amide groups, as confirmed by ab initio calculations. 

This chapter is devoted to a consideration of the results obtained in studies of the interactions of nitrogen oxides with polymers. There are eight nitrogen oxides, but only NO, NO2 and N-,04 are actually important as pollutants. Nitric oxide (NO) exists as a free radical, but it is reasonably stable in reactions with organic compounds. The paramagnetic nitrogen dioxide (NO2) is more active compared with NO. This gas is universally present in equilibrium with its dimer molecule ... 

An exception is the case that a critical reaction step takes place in the gas phase only. An interesting example is the nitric acid process, where evolved nitrous oxide is oxidized to nitrogen dioxide in the gas phase. The dioxide (or its dimer) dissolves again and reacts with water. In this process both the gas volume and the gas/liquid interfacial area determine the overall reaction rate. Of course, gas/liquid mass transfer has then to be taken into account (section 4.6). 

The nitric oxide which is formed reacts with oxygen to form nitrogen dioxide. Nitrogen dioxide exists in equilibrium with its dimer, dinitrogen tetroxide. The nitrogen dioxide/dimer mixture is sent to a column, sometimes called an absorption tower. Water is added at the top of the column. The nitrogen dioxide is converted to nitric acid. Byproduct nitric oxide is oxidized to nitrogen dioxide by means of a stream of air passed into the absorption column. The aqueous nitric acid is removed continuously from the base of the column. Overall, the reaction can be written as ... 

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