Nitrogen nitrites

For other forms of nitrogen, nitrite and organic constituents, few techniques have been proposed due to the lesser importance of nitrite in wastewater management (low concentration and non-stable), and to the difficulty in being selective for the organic forms. 

Figure 10.8. Flow diagram for the determination of ammonia, organic nitrogen, nitrite, and nitrate using Kjeldahl apparatus [6].

The most common salt mixture used is a eutectic blend of 40% sodium nitrite, 7% sodium nitrate, and 53% potassium nitrate. Its temperature range is from 150°C to 540°C. The melting point of a fresh mixture of this salt composition is 142°C. However, sodium nitrite slowly undergoes endothermic breakdown to form sodium nitrate, sodium oxide, and nitrogen. Nitrite can also undergo oxidation to form nitrate. This process results in the increase of its melting point. It can react with carbon dioxide to form carbonates and with water to form hydroxides. 

Oxidized nitrogen. Nitrite ion, in presence of acetic acid, does not oxidize Ni (distinction from Co). 

Oxidized nitrogen. Nitrite complexes Zn, unlike Cd, only up to Zn(N02)2-Nitrate, however, goes up to [Zn(7 -N03)4] . 

Oxidized nitrogen. Nitrites in acid readily decompose arsane ... 

If this reaction takes place in air, the evolved nitrogen monoxide is oxidised to the dioxide and this dissolves again as in equation (9.1) hence virtually complete conversion of nitrogen dioxide to nitric acid can occur (see nitric acid, below). With alkalis, a mixture of nitrite and nitrate is formed ... 

C2H5ONO + NaOH C2H5OH + NaNOa sodium nitrite. The second compound is nitroethane, C,H NO, of b.p. 114° its identity is clearly shown by the action of reducing agents, which convert it into ethylamiiie, CjHjNHj, thus proving the presence of a nitrogen carbon... 

Lassaigne s test is obviously a test also for carbon in the presence of nitrogen. It can be used therefore to detect nitrogen in carbon-free inorganic compounds, e.g., complex nitrites, amino-sulphonic acid derivatives, etc., but such compounds must before fusion with sodium be mixed with some non-volatile nitrogen-free organic compound such as starch... 

The evolution of nitrogen is not always entirely satisfactory as a test owing to the possible evolution of gaseous decomposition products of nitrous acid itself. The test may be performed as follows. To i ml. of chilled concentrated sodium nitrite solution add i ml. of dilute acetic acid. Allow any preliminary evolution of gas to subside, and then add the mixed solution to a cold aqueous solution (or suspension) of the amide note the brisk effervescence. 

It is advisable to add the sodium nitrite solution, particularly in preparations on a larger scale, through a separatory or dropping funnel with the tip of the stem extending well below the sui-face of the liquid tliis will prevent loss of nitrous acid by surface decomposition into oxides of nitrogen. 

An alternative method of removing the aniline is to add 30 ml. of concentrated sulphuric acid carefully to the steam distillate, cool the solution to 0-5°, and add a concentrated solution of sodium nitrite until a drop of the reaction mixture colours potassium iodide - starch paper a deep blue instantly. As the diazotisation approaches completion, the reaction becomes slow it will therefore be necessary to teat for excess of nitrous acid after an interval of 5 minutes, stirring all the whUe. About 12 g. of sodium nitrite are usually required. The diazotised solution is then heated on a boiling water bath for an hour (or until active evolution of nitrogen ceases), treated with a solution of 60 g. of sodium hydroxide in 200 ml. of water, the mixture steam-distilled, and the quinoline isolated from the distillate by extrsM-tion with ether as above. 

Triiodobeiizoic acid. Dissolve 6-8 g. of 3 5-diiodo-4-aminobenzoic acid in 30 ml. of cold concentrated sulphuric acid, add a large excess (3 0 g.) of powdered sodium nitrite, and allow the mixture to stand at 0° for 2 hours. Treat the cold diazonium solution with a solution of 17 0 g. of potassium iodide in 40 ml. of water a dark red precipitate separates. Warm the mixture on a water bath until the evolution of nitrogen ceases, and remove any residual iodine with a little... 

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