By oxidation of nitrogen

N-nitrosation by oxides of nitrogen at neutral and alkaline pH has an important bearing on assessing human exposure to N-nitroso compounds, particularly as this route has been almost totally disregarded in the past. Those analytical techniques which have relied on a basic pH to inhibit nitrosation need further study to ensure the validity of the findings. For the same reason, measurements of N-nitrosamines in engine exhausts and tobacco smoke are likely to be particularly artifact prone. 

The reactions of nitric oxide involve either oxidation or reduction (or both simultaneously in disproportionation and decomposition). Except for oxidation, these reactions of nitric oxide require catalysts for them to proceed at significant rates. An important stimulus to studying these catalyzed reactions lies in the environmental hazards posed by oxides of nitrogen, of which NO is the parent member, as discussed at the beginning of this section. Particular attention in the area of metal complex catalyzed reactions has focused in the last five years on the reduction of nitric oxide by carbon monoxide, (113). 

Nitrate, which is produced by oxidation of nitrogen, is a monovalent polyanion having the formula N03. Most metal nitrates are soluble in water and occur in trace amounts in surface- and groundwaters. Nitrate is toxic to human health and, chronic exposure to high concentrations of nitrate, may cause methemoglobinemia. Maximum contaminant limit in potable water imposed by U.S. EPA is 10 mg nitrate as nitrogen/L. 

This is prepared on an enormous scale by the lead chamber and contact processes. In the former, S02 oxidation is catalyzed by oxides of nitrogen (by intermediate formation of nitrosylsulfuric acid, H0S020N0) in the latter, heterogeneous catalysts such as Pt are used for the oxidation. Pure H2S04 is a colorless liquid that is obtained from the commercial 98% acid by addition first of S03 or oleum and then titration with water until the correct specific conductance or melting point is achieved. 

The gas mixture obtained by oxidation of nitrogen(ll) oxide, containing nitrogen(lV) oxide and dinitrogen(lV) oxide (so-called nitrous gases), is reacted in the third reaction step with water as follows ... 

While a number of synthetic routes are available to various sulfoxides, the primary methods for commercial production of DMSO involve oxidation of dimethyl sulfide by oxides of nitrogen or by air in the presence of NO cat-alyst.f Dimethyl sulfoxide is both the product and the reaction solvent. To alleviate the potential for exothermic, and potentially explosive, runaway reactions in these oxidations, the feed rate for dimethyl sulfide is adjusted to ensure complete conversion and, thus, low instantaneous concentrations at any time. Alternate oxidants for the conversion of sulfides to sulfoxides include nitric acid, H202/acetic acid, peracids, and halogen/water. ... 

Apart from releasing photosynthetically reduced carbon and exporting elec-Irons, microbes also catalyze extracellular redox and hydrolysis reactions on I heir surfaces using external substrates. Of particular interest in our discussion is i class of surface enzymes in phytoplankton, deaminases, that catalyze the iclease of NII4 by oxidation of nitrogen containing compounds (Palcnik, 1989)... 

Nitration of aromatic compounds by oxides of nitrogen and ozone. 

Chamber An obsolete but formerly very important process for making sulfuric acid. Invented by J. Roebuck in Birmingham, England, in 1746, although the patent was not filed in Scotland until 1771. Progressively improved during the nineteenth century and finally abandoned everywhere in favor of the Contact process by 1980. Essentially, the Chamber process was the gas-phase oxidation of sulfur dioxide to sulfur trioxide, catalyzed by oxides of nitrogen, conducted in a lead-lined chamber, followed by dissolution of the sulfur trioxide in water. 

Sulfurdioxide is the main cause of acid rain. Its oxidation to sulfur trioxide is catalysed by oxides of nitrogen. 

There are many acidic oxide gases that react with refractories. They are oxides of nitrogen and sulfur. The nitrates produced by oxides of nitrogen have low melting points. SO2 and SO3 form liquid sulfates. Volatile oxides of arsenic are encountered in some nonferrous metal operations, and are corrosive. The volatile basic oxides are the alkalis K2O and Na20, and their corresponding hydroxides KOH and NaOH. These react with the refractories that contain them and yield products that are almost always low-melting. 

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