Sulfanilic acid nitration

Nitrate is of interest as a possible indication of watering. Many potable water supplies contain 30 mg/liter of nitrate whereas normal wines contain about 4-5 mg/liter on the average (46,47,48). The present recommended procedure (49) is reduction of nitrate to nitrite followed by colorimetric determination with sulfanilic acid and a-naphthylamine. 

A method [17] has been described for the determination of nitrate and nitrite nitrogen and ammonium ions in the 2 M potassium chloride extracts of moist soils. Firstly, an aliquot of the extract is made alkaline and the released ammonia determined via an ammonia-selective probe or titrimetrically. The nitrate in the ammonia-free extract is then reduced to ammonia with Devarda s alloy and the ammonia removed by distillation and determined titrimetrically. The concentration of nitrite in the extract is then determined spectrophoto-metrically as the red dye formed by coupling diazotised sulfanilic acid with N naphthylethylenediamine hydro chloride. 

Nitrite is determined spectrophotometrically at 550 nm after treatment with sulfanilic acid and N-1 -naphlhylclhylencdiamine to form the azo dye. In another portion of the sample, nitrate is reduced to nitrite by passing the solution buffered to pH 9.6 through a cadmium reductor, and total nitrite is determined as above. 

The previous argument would suggest that in even less basic anilines the reaction of the nitrating acid should be exclusively directed towards the small fraction of unprotonated amine. This would mean that anilines of this type would be nitrated in ortho- and/or /mra-position instead of the meta-position. This idea is illustrated in the nitration of sulfanilic acid (Figure 5.22), which proceeds ortho to the H2N group and meta to the S03H of the free amine B instead of meta to the H3N group of the anilinium cation D. 

Fig. 5.22. Nitration of sulfanilic acid B and desulfonation of the nitration product G. The protonation product D of the substrate is a benzene derivative with two strong electron acceptors (S03H and H3N ) and therefore cannot form a sigma complex under the reacdtion conditions. The fact that an Ar-SE reaction occurs nonetheless is due to the small equilibrium amount of the neutral form B of sulfanilic acid. B is nitrated in ortho-position to the electron donor (H2N) and thus in meta-position to the electron acceptor (S03H).

Both the reference and sample cuvettes contained 5.16 X 10"3M sulfanilic acid and 8.3 X 10"4M NEDA. The reaction was initiated by adding nitrate (final concentration = 1.33 X 102M) to the sample cuvette. The average ratio and standard deviation of k0bs /k0bs was 2.08 0.10. 

Experiments were carried out in a 500-mL photochemical reactor with a quartz immersion well. A 10 x 20 cm2 piece of film was wrapped around the immersion well and tied in place with Teflon tape. Then 350 mL of H20 was placed in the reactor and NaOH was added to adjust the pH to 12. The system was purged continuously with air or N2 and irradiated with a 400-W medium-pressure Hg lamp. After a period of time the solution was tested for NH3 by the indophenol method, and for NOJ/NOJ (combined total nitrite and nitrate) by Cd reduction, followed by colorimetric analysis by the azo-dye method [84]. The azo-dye method, sometimes known as the Griess method or the sulfanilic acid method, has been described elsewhere [87]. 

OTHER COMMENTS alpha-Naphthylamine is an extremely toxic chemical in any of its physical forms, such as flake, dust, liquid, or vapor may be fatal if absorbed through skin, if inhaled, or swallowed personnel should be completely protected against physical contact with this chemical this chemical has been used in the manufacture of dyes and toning prints made with cerium salts the hydrochloride with sulfanilic acid is a reagent for nitrate. 

For fast reactions of the type represented by reaction 13.2, carried out under the conditions stated earlier, micromixing becomes the dominant consideration. However, studies on the effect of micromixing in such reactions are sparse. Some examples are as follows nitration of aromatic componds in general (Schofield, 1980), potassium metal-provoked reactions of aryl halides with amide and acetone enolate ions (Tremelling and Bunnett, 1980X coupling of 1-naphthol with diazotized sulfanilic acid (Bourne et al., 1981, 1985), reactions of o-(3-butenyl)-halobenzenes and 6-bromo-1-hexene with alkali metals in ammonia/terr-butyl alcohol solution (Meijs et al., 1986), and monoacylation of symmetrical diamines (Jacobson et al., 1987). In some fast reactions, hydrogen ions are produced. 

Nitrite may be determined by its absorbance at 522 nm after extraction from foods such as cheese or flour and reaction with a color reagent comprising sulfanilic acid and 1-naphthylamine in aqueous acetic acid. Nitrate is determined by this method after reduction to nitrites using cadmium in a modified Jones Reductor as described in AOAC method 976.14. 

The most representative example of this type of reaction is the so-called Griess reaction, originally developed for the kinetic determination of nitrite. Nitrite in a weakly acidic solution reacts with an amine (usually sulfanilic acid) to form the corresponding diazonium salt, which then couples with a naphthylamine or naphthol. This reaction can also be used for the kinetic determination of nitrate after reduction in a column, as well as for measuring other species such as sulfonamides (Bratton-Marshall reaction), and benzodiazepines and N-methylcarba-mate pesticides, the hydrolysis of which yields the corresponding benzophenones (which can be diazoti-zed) and naphthols (useful for the coupling reaction), respectively. 

Procedure. A drop of the neutral or acetic acid solution is mixed on a spot plate with a drop of sulfanilic acid solution and a drop of a-naphthylamine solution a few milligrams of zinc dust are added. In the presence of nitrates, a red coloration gradually develops. 

Recently, layer-by-layer assemblies of polystyrene-based diazonium salt (DPS) and sulfonated reduced graphene oxide (SRGrO) were deposited on quartz, silicon, and ITO substrates [300]. The DPS was prepared from polystyrene (PS) through nitration, reduction, and diazotization reaction, whereas SRGrO was prereduced with NaBH4, modified with diazonium salt of sulfanilic acid, and reduced by hydrazine. Besides a spontaneous reaction between DPS and SRGrO, the... 

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