Nitrous acid analytical reactions

Analytical and Laboratory Operations. Sulfamic acid has been recommended as a reference standard in acidimetry (55). It can be purified by recrystaUization to give a stable product that is 99.95 wt % pure. The reaction with nitrite as used in the sulfamic acid analytical method has also been adapted for determination of nitrites with the acid as the reagent. This reaction is used commercially in other systems for removal of nitrous acid impurities, eg, in sulfuric and hydrochloric acid purification operations. 

Nitrosothiols are also readily decomposed by mercuric ion to the corresponding coordinated thiols and nitrous acid (in acid solution) as in equation 16. This reaction has been used as the basis of an analytical procedure for thiol determination30. Mechanistic... 

The presence of HMX as an impurity in RDX is not a problem when the product is used as an explosive. However, the need for an analytical sample of RDX makes other more indirect methods feasible. One such method involves the oxidation of 1,3,5-trinitroso-1,3,5-triazacyclohexane (109) ( R-salt ) with a mixture of hydrogen peroxide in nitric acid at subambient temperature and yields analytical pure RDX (74%) free from HMX." The same conversion has been reported in 32 % yield with three equivalents of a 25 % solution of dinitrogen pentoxide in absolute nitric acid. l,3,5-Trinitroso-l,3,5-triazacyclohexane (109) is conveniently prepared from the reaction of hexamine with nitrous acid at high acidity. ... 

A kinetic method for determination of aromatic amines was proposed, based on measuring the development of azo dyes (134) resulting from coupling a diazonium ion derived from a PAA analyte and the chromophoric substrate 1 -(4-hydroxy-6-methylpyrimidin-2-yl)-3-methylpyrazolin-5-one (133), as shown in equation 22. After a short induction period initial rate kinetics can be measured when the process is quite advanced, absorbance reaches a maximum and starts to recede due to oxidation of the azo dye by excess nitrous acid. Each PAA has to be calibrated for its molar absorption coefficient and reaction rate, for optimal measurement. A tenfold excess of 133 over the analytes ensures a pseudo... 

Use Diazotization (by reaction with hydrochloric acid to form nitrous acid) rubber accelerators color fixative and preservative in cured meats, meat products, fish pharmaceuticals photographic and analytical reagent dye manufacture antidote for cyanide poisoning. 

Catechol and hydroquinol are also attacked by nitrous acid, but the reducible products of this reaction were not identified. Nevertheless, the two waves resulting from the reaction of the catechol grouping in rutin with nitrous acid can be used for analytical purposes. Similarly quecitrin can also be determined. In a similar manner and by following the procedure given for morphine, cephaeline was determined, although the structure of the reducible compound has not been proved. In the determination, a 100-foId excess of emetine does not interfere and it can be applied to tinctura ipecacuanhae and injections. 

Beyond about pH = 5, nitrite ions are stable. However, we must moderate what is said about the disproportionation of nitrous acid, because of the fact that it is slow. This gives us time to carry out some analytical reactions. 

Although the reaction of nitrous acid with peptides and proteins has been extensively used for analytical purposes (van Slyke estimation), the nature of the organic products has often been overlooked. Recently, Bonnett and Holleyhead 49) reported that treatment of N-acyl-tryptophan derivatives with sodium nitrite under mildly acidic conditions furnishes nitrosamines with the nitroso group located at the indolic nitrogen. 

Negative chemical ionization by proton removal (deprotonation) by a base to provide (M - H) ions is used rarely now except in research laboratories. It concerns molecules whose acidic hydrogens are easy to detach with a base. If one wants to use hydroxyl OH ions as basic reagents, one can for example form a hydroxyl by using a mixture of nitrous oxide and methane. Figure 9.62 illustrates the mechanisms of dissociative electron capture on N2O to form the O ion (reaction 3) and abstraction of a hydrogen atom from methane by O to form OH (reaction 4). The OH ion can then abstract a proton from the analyte to form the (M - H) ion (reaction 5). 

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