Nitric acid synthesis from nitrogen dioxide

Abstract Synthesis methods of various C- and /V-nitroderivativcs of five-membered azoles - pyrazoles, imidazoles, 1,2,3-triazoles, 1,2,4-triazoles, oxazoles, oxadiazoles, isoxazoles, thiazoles, thiadiazoles, isothiazoles, selenazoles and tetrazoles - are summarized and critically discussed. The special attention focuses on the nitration reaction of azoles with nitric acid or sulfuric-nitric acid mixture, one of the main synthetic routes to nitroazoles. The nitration reactions with such nitrating agents as acetylnitrate, nitric acid/trifluoroacetic anhydride, nitrogen dioxide, nitrogen tetrox-ide, nitronium tetrafluoroborate, V-nitropicolinium tetrafluoroborate are reported. General information on the theory of electrophilic nitration of aromatic compounds is included in the chapter covering synthetic methods. The kinetics and mechanisms of nitration of five-membered azoles are considered. The nitroazole preparation from different cyclic systems or from aminoazoles or based on heterocyclization is the subject of wide speculation. The particular section is devoted to the chemistry of extraordinary class of nitroazoles - polynitroazoles. Vicarious nucleophilic substitution (VNS) reaction in nitroazoles is reviewed in detail. 

Industrial fertilizer synthesis starts from ammonia synthesis, and ammonia is then easily oxidized in a separate reactor to nitric oxide over PtRh wire gauze catalyst. Formation of nitric acid requires further oxidation of nitric oxide to nitrogen dioxide (NO2) and absorption of the nitrogen dioxide in water. Overall, three different chemical process plants are used for the synthesis of nitric acid. The ammonia synthesis reaction takes place in a high-tem-perature, high-pressure reactor that requires recycling of products due to the thermodynamic limitations of chanical conversion. The ammonia oxidation reaction is very fast and takes place over a very small reactor length. Finally, nitric acid synthesis takes place in absorption columns. 

Nitroalkanes can be formed from the direct nitration of aliphatic and alicyclic hydrocarbons with either nitric acid ° or nitrogen dioxide in the vapour phase at elevated temperature. These reactions have achieved industrial importance but are of no value for the synthesis of nitroalkanes on a laboratory scale, although experiments have been conducted on a small scale in sealed tubes. 

The oxidation of cyclohexanone by nitric acid leads to the generation of nitrogen dioxide, nitric oxide, and nitrous oxide. The first two gases can be recycled for the synthesis of nitric acid. Nitrous oxide, however, is an ozone depleter and cannot be recycled. Indiscriminate nitrous oxide emission from this process is therefore the cause of considerable concern. As shown by 8.9, part of the cyclohexanone can also be converted to the corresponding oxime and then to caprolactam—the monomer for nylon 6. Phthalic acids are one of the monomers for the manufacture of polyesters. As shown by Eq. 8.10, it is made by the oxidation of p-xylene. A general description of polyamides (nylons) and polyesters are given in Section 8.4. 

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