Nitrites analytical reactions

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. 

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. 

Co. and 20 mM nitrite in water, pH 3, 25 C, 60 min reaction], it was nitrosated to yield 3.62 mM 2,6-dimethyl-N-nitrosomorpho-line (DMNM), which was a 10% greater yield than that for a similar nitrosation of morpholine to give NMOR. This indicated a slightly larger rate constant for DMNM than for NMOR formation (3). Crude DMM is a 2 1 mixture of the cis and trans isomers ( 0). GC analysis of the product of the kinetic run showed that the 2 isomers were nitrosated at similar rates. Cis-DMNM [retention time (RT), 320 sec] was well separated from NMOR (RT, 430 sec), but trans-DMNM (RT, 405 sec) was not. Accordingly, we prepared pure cis-DMM, b.p. 133 C, by spinning-band fractional distillation of crude DMM and used it in the analytical procedure. The RT of N-nitrosopyrrolidine (NPYR) was 390 sec. 

In fact, as will be indicated later in this manuscript, the proteins of meat are the major constituent with which nitrite reacts and explain the largest proportion of the nitrite lost from analytical detection during curing. While considerable discussion has occurred about this so called protein bound nitrite, little has been substantiated about identification and quantitation of the reaction products. Protein bound nitrite has been of concern in analysis for free nitrite because depending on conditions of analysis, some portion of it may be released and measured. 

Chemiluminescent techniques have been used to determine nanomolar quantities of nitrate and nitrite in seawater [124,125]. This method depends on the selective reduction of these species to nitric oxide, which is then determined by its chemiluminescent reaction with ozone, using a commercial nitrogen oxides analyser. The necessary equipment is compact and sufficiently sturdy to allow shipboard use. A precision of 2nmol/l is claimed, and an analytical range of 2nmol/l with analysis rates of 10-12 samples hourly. 

Peroxyoxalate-based CL reactions are related to the hydrogen peroxide oxidation of an aryl oxalate ester, producing a high-energy intermediate. This intermediate (l,2-dioxetane-3,4-dione) forms, in the presence of a fluorophore, a charge transfer complex that dissociates to yield an excited-state fluorophore, which then emits. This type of CL reaction can be used to determine hydrogen peroxide or fluorophores including polycyclic aromatic hydrocarbons, dansyl- or fluores-camine-labeled analytes, or, indirectly, nonfluorescers that are easily oxidized (e.g., sulfite, nitrite) and quench the emission. The most widely used oxalate... 

The oxidizing agents are nitrate and nitrite ions, formed by the action of sulfuric acid on explosives. This reaction, a classical test for nitrate ions [4], is not specific it involves only oxidation/reduction and no atoms from the analyte are incorporated... 

Principally the same, but chemically simpler, sequence was used to prepare arylnitro anion-radicals from arylamines, in high yields. For instance, aqueous sodium nitrite solution was added to a mixture of ascorbic acid and sodium 3,5-dibromo-4-aminobenzenesulfonate in water. After addition of aqueous sodium hydroxide solution, the cation-radical of sodium 3,5-dibromo-4-nitro-benzenesulfonate was formed in the solution. The latter was completely characterized by its ESR spectrum. Double functions of the nitrite and ascorbic acid in the reaction should be underlined. Nitrite takes part in diazotization of the starting amine and trapping of the phenyl a-radical formed after one-electron reduction of the intermediary diazo compound. Ascorbic acid produces acidity to the reaction solution (needed for diazotization) and plays the role of a reductant when the medium becomes alkaline. The method described was proposed for ESR analytical determination of nitrite ions in water solutions (Lagercrantz 1998). 

Some reactions o nitrons acid and the nitrites of analytical interest.—Many... 

Carboxyphenyl Phenyl Tellurium2 27.2 g (0.2 mol) of 2-aminobcnzoic acid arc dissolved in a mixture of 25 ml of concentrated hydrochloric acid and 70 ml of water. 13.8 g of sodium nitrite dissolved in 20 ml of water are added dropwisc to the stirred amine solution cooled in an icc/walcr bath. Sodium hydrogen carbonate is added until the solution of the diazonium salt is slightly basic. 23 g (56 mmol) of diphenyl ditellurium are dissolved in a mixture of 30 ml of ethanol and 60 ml of THF. To this solution are added 2.3 g (60 mmol) of sodium borohydride dissolved in 33 ml of 1 M aqueous sodium hydroxide. The diazonium salt solution is quickly added to the warm benzenetellurolate solution. 10 ml of 1 M sodium hydroxide are then added and, after the evolution of nitrogen has ceased, the mixture is heated to complete the reaction. The mixture is poured onto ice and diphenyl ditellurium is extracted with benzene. The aqueous phase is acidified with 1 M hydrochloric acid and the product precipitates in analytically pure form yield 28.2 g (43%) m.p. 185° (from toluene). 

The acid hydrolysis of the 2-aryl-1,3,4-oxadiazoles can be used for their analytical determination. The method used is either to break down the compound by heating with hydrochloric acid under reflux to give the acid hydrazide and then to titrate the hydrazide with iodide in bicarbonate solution,68, 69 or to titrate potentiometrically directly with sodium nitrite in a hydrochloric acid medium.128 In this way the acid hydrazide is formed in the first reaction step and is then converted into the insoluble azide by the sodium nitrite. 

Therefore, pouring sulfuric acid over nitrites results in the formation of both NO and NO2. Nitrates do not form brown gases on reaction with sulfuric acid, a reaction that is used for the analytic distinction between nitrates and nitrites. 

Study of Color Forming Reactions of Tryptophan, p-Dimethylamino-benzaldehyde, and Sodium Nitrite in Sulfuric Acid Solution. Analyt. Chem. 20, 30 (1948). 

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