Nitrous acid nitration catalyst

Adsorption of nitric and sulfuric acids on ice particles provides the sol of the nitrating mixture. An important catalyst of aromatic nitration, nitrous acid, is typical for polluted atmospheres. Combustion sources contribute to air pollution via soot and NO emissions. The observed formation of HNO2 results from the reduction of nitrogen oxides in the presence of water by C—O and C—H groups in soot (Ammann et al. 1998). As seen, gas-phase nitration is important ecologically. 

NITROUS ACID AS A NITRATION CATALYST AND AS A NITRATING AGENT... 

In his work on the nitration kinetics, which has already been referred to, Mar-tinsen [145] found that in the nitration of phenol with nitric acid, nitrous acid, if present, acted as a catalyst on the nitration process. The presence of nitrous acid was necessary for initiating the reaction, further quantities being formed in the reaction of oxidation of phenol with nitric acid, which accompanied the nitration reaction. Thus the reaction of nitrating phenol is an autocatalytic one. 

Nitrous acid as a nitrating catalyst and as nitrating agent... 

AUcynes and allenes are formed by the acylation of nitrimines using acetic anhydride/pyridine with DMAP as catalyst (eqs 67 and 68). Nitrimines are prepared by nitration of ketoximes with nitrous acid. 

Hydrogenation catalyst, Acid, Fuel Riesthuis, P. et al., J. Loss Prev. Process Ind., 1997, 10(10), 67 In the presence of precious metal hydrogenation catalyst, hydroxylamine salts may disproportionate and form dinitrogen monoxide. Such a mixture is present in a process whereby the hydroxyamine is formed by hydrogenation of nitrate. An explosion in the degassing line, after a period of abnormal operation, was attributed to nitrous oxide build-up. Fuel, in the form of hydrogen and methane diluent, was already present. 

Fluorobenzene is hydroxylated in 90% yield with nitrous oxide (N,0) over a zeolite catalyst, but a mixture of regioisomers is formed (Table 7).1091,2,4,5-Tetrafluorobenzene is oxidized, instead of nitrated, by fuming nitrie acid to 2,5-difluoro-l,4-bcnzoquinone (1) in low yield.1,0... 

Many catalysts used in chemical synthesis can be treated in the same way, often the nitrous oxide/acetylene flame is used because of the refractory nature of the elements to be determined. Harrington and Bramstedt [56] have determined rhenium in electro-chemical surface catalysts by stripping the coating with molten potassium hydroxide/ potassium nitrate. This melt was extracted with hydrochloric acid, the residue was fused with sodium peroxide for further rhenium determination. Titanium, being the substrate on which the catalyst was coated, was added to the standards, an air/acetylene flame and 343.3 nm were used for the finish. 

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