Additives nitrite

However, questions have been raised about the possible effects of these additives on human health. Nitrites, for example, appear to decrease the ability of a young child s blood to carry oxygen. In addition, nitrites combine with organic compounds known as amines to form a family of toxic compounds known as the nitrosoamines. These hazards have prompted some scientists and nonscientists alike to call for the ban of nitrates and nitrites as food additives. 

Most plants can utilize directly ammonia, nitrates and a few organic compounds such as urea, amino acids and amides. In addition, nitrite is usually assimilated readily, but at soil concentrations greater than about 10—20 p.p.m. is likely to produce signs of toxicity. 

Later, we will see that NO2 will again be converted to nitrite (5.206) via electron transfer processes independent of the reaction chain (5.201) to (5.203), thereby establishing dynamic equilibria. In the presence of formate HCOO , which is an efficient OH radical scavenger, it not only prevents nitrite losses via reaction (5.191), but actually converts NO2, the major product of nitrate photolysis, into additional nitrite via the following reaction sequence = 4.3 10 L mol s and ks 202 = 2.4 10 L mol s ... 

After a period of 4-5 min, check the clear solution of anthranyldiazonium chloride for the presence of excess nitrous acid by placing a drop of the solution on a piece of potassium iodide-starch test paper. If an excess is present, the test paper gives an immediate blue color. If no color is obtained, prepare additional nitrite solution and add as before until a positive test is observed. 

Ammonia will not be oxidized to nitrite before the reaction of iodine with the thiosulphate in the sample has taken place. Nitrite will also react with iodine therefore, the surplus iodine must be determined rapidly in order to avoid formation of additional nitrite by oxidation of ammonia. The reactions are as follows ... 

Nitrous acid, HNOj, is known as a gas, but otherwise exists only in solution, in which it is a weak acid. Hence addition of a strong acid to a solution of a nitrite produces the free nitrous acid in solution. 

The addition of even a weak acid (such as ethanoic acid) to a nitrite produces nitrous acid which readily decomposes as already indicated. Hence a nitrite is distinguished from a nitrate by the evolution of nitrous fumes when ethanoic acid is added. 

Addition of excess potassium nitrite acidified with ethanoic acid gives a precipitate of the potassium hexanitro-cobaltate(lll), K3[Co(N02)6] (P. 403). 

The solution of the aniline hydrochloride should be cooled to 5°C., and this temperature maintained throughout the addition of the sodium nitrite solution. External cooling has to be maintained, otherwise the heat of the reaction would cause the temperature to rise, with the consequent decomposition of the diazonium chloride and the production of phenol. If, on the other hand, the temperature is reduced to about o , diazotisation becomes extremely slow and unchanged nitrous acid may remain in the solution for an impracticably long time. 

To ensure the presence of a slight excels of nitrous acid, potassium iodide-starch paper is sometimes used as an external indicator, a drop of the solution being removed from time to time during the addition of the sodium nitrite, and then dropped on to the paper. When an excess of nitrous acid is present, iodine is liberated, and gives the familiar... 

Dissolve 15 ml. (15-4 g.) of aniline in a mixture of 40 ml. of concentrated hydrochloric acid and 40 ml. of water contained in a 250 ml. conical flask. Place a thermometer in the solution, immerse the flask in a mixture of ice and water, and cool until the temperature of the stirred solution reaches 5°. Dissolve I2 5 g. of powdered sodium nitrite in 30 ml. of water, and add this solution in small quantities (about 2-3 ml. at a time) to the cold aniline hydrochloride solution, meanwhile keeping the latter well stirred by means of a thermometer. Heat is evolved by the reaction, and therefore a short interval should be allowed between consecutive additions of the sodium nitrite, partly to allow the temperature to fall again to 5°, and partly to ensure that the nitrous acid formed reacts as completely as possible with the aniline. The temperature must not be allowed to rise above 10°, otherwise appreciable decomposition of the diazonium compound to phenol will occur on the other hand, the temperature... 

Add 20 g. of /)-bromoaniline to 20 ml. of water in a 250 ml. beaker, and warm the mixture until the amine melts. Now add 23 ml. of concentrated hydrochloric acid and without delay stir the mixture mechanically in an ice-water bath, so that a paste of fine /> bromo-aniline hydrochloride crystals separates. Maintain the temperature of the stirred mixture at about 5° whilst slowly adding from a dropping-funnel a solution of 8 5 g. of sodium nitrite in 20 ml. of water con tinue the stirring for 20 minutes after the complete addition of the nitrite. 

Dissolve 4 5 ml. of aniline in a mixture of 10 ml. of concentrated hydrochloric acid and 20 ml. of water cool the solution to 5°, and diazotise by the addition of 4 g. of sodium nitrite dissolved in 20 ml, of water, observing the usual precautions given on page 181. Dissolve 7 g. of 2-naphthol in 60 ml. of 10% sodium hydroxide solution contained in a 200 ml. beaker, and cool this solution to 5 by external cooling, aided by the direct addition of about 20-30 g. of crushed ice. Now add the diazotised solution very slowly to the naphthol solution, keeping the latter well stirred meanwhile the mixed solutions immediately develop a deep red colour, and the benzeneazonaphthol should... 

Equip a 1-litre three-necked flask with a powerful mechanical stirrer, a separatory funnel with stem extending to the bottom of the flask, and a thermometer. Cool the flask in a mixture of ice and salt. Place a solution of 95 g. of A.R. sodium nitrite in 375 ml. of water in the flask and stir. When the temperature has fallen to 0° (or slightly below) introduce slowly from the separatory funnel a mixture of 25 ml. of water, 62 5 g. (34 ml.) of concentrated sulphuric acid and 110 g. (135 ml.) of n-amyl alcohol, which has previously been cooled to 0°. The rate of addition must be controlled so that the temperature is maintained at 1° the addition takes 45-60 minutes. AUow the mixture to stand for 1 5 hours and then filter from the precipitated sodium sulphate (1). Separate the upper yellow n-amyl nitrite layer, wash it with a solution containing 1 g. of sodium bicarbonate and 12 5 g. of sodium chloride in 50 ml. of water, and dry it with 5-7 g. of anhydrous magnesium sulphate. The resulting crude n-amyl nitrite (107 g.) is satisfactory for many purposes (2). Upon distillation, it passes over largely at 104° with negligible decomposition. The b.p. under reduced pressure is 29°/40 mm. 

To prepare the solid phenyldlazonlum chloride or sulphate, the reaction is conducted in the absence of water as far as possible. Thus the source of nitrous acid is one of its organic esters (e.g., amyl nitrite) and a solution of hydrogen chloride gas in absolute alcohol upon the addition of ether only the diazonium salt is precipitated as a crystalline solid, for example ... 

Dissolve 3-5 g. of aniline hydrochloride in 20 ml. of absolute ethyl alcohol contained in a 50 ml. conical flask, and add 0-5 ml. of a saturate solution of hydrogen chloride in absolute ethyl alcohol. Cool in ice and add 4 g. (4 -6 ml.) of iso-amyl nitrite (compare Section 111,53) gradually. Allow the mixture to stand for 5-10 minutes at the room temperature, and precipitate the diazonium salt by the gradual addition of ether. Filter ofiF the crystals at the pump on a small Buchner funnel, wash it with 5 ml. of alcohol - ether (1 1), and then with 10 ml. of ether. Keep... 

Dissolve 36 g. of p-toluidine in 85 ml. of concentrated hydrochloric acid and 85 ml. of water contained in a 750 ml. conical flask or beaker. Cool the mixture to 0° in an ice-salt bath with vigorous stirring or shaking and the addition of a httle crushed ice. The salt, p-toluidine hydrochloride, will separate as a finely-divided crystalline precipitate. Add during 10-15 minutes a solution of 24 g. of sodium nitrite in 50 ml. of water (1) shake or stir the solution well during the diazotisation, and keep the mixture at a temperature of 0-5° by the addition of a httle crushed ice from time to time. The hydrochloride wUl dissolve as the very soluble diazonium salt is formed when ah the nitrite solution has been introduced, the solution should contain a trace of free nitrous acid. Test with potassium iodide - starch paper (see Section IV,60). 

In a 1 or 1-5 htre round-bottomed flask prepare a solution of 53-5 g. of o-toluidine in 170 ml. of 48 per cent, hydrobromic acid, cool to 5° by immersion in a bath of ice and salt. Diazotise by the gradual addition of a solution of 36 -5 g. of sodium nitrite in 50 ml. of water stopper the flask after each addition and shake until all red fumes are absorbed. Keep the temperature between 5° and 10°. When the diazotisation is complete, add 2 g. of copper powder or copper bronze, attach a reflux condenser to the flask, and heat very cautiously on a water bath. Immediately evolution of gas occurs, cool the flask in crushed ice unless the... 

Dissolve 46-5 g. (45-5 ml.) of aniUne in a mixture of 126 ml. of concentrated hydrochloric acid and 126 ml. of water contained in a 1-htre beaker. Cool to 0-5° in a bath of ice and salt, and add a solution of 36-5 g. of sodium nitrite in 75 ml. of water in small portions stir vigorously with a thermometer (1) and maintain the temperature below 10°, but preferably at about 5° by the addition of a httle crushed ice if necessary. The diazotisation is complete when a drop of the solution diluted with 3-4 drops of water gives an immediate blue colouration with potassium iodide - starch paper the test should be performed 3-4 minutes after the last addition of the nitrite solution. Prepare a solution of 76 g. of sodium fluoborate (2) in 150 ml. of water, cool, and add the chilled solution slowly to the diazonium salt solution the latter must be kept well stirred (1) and the temperature controlled so that it is below 10°. Allow to stand for 10 minutes with frequent stirring. Filter... 

Dissolve 5 0 g. (4-9 ml.) of aniline in 16 ml. of concentrated hydrochloric acid and 16 ml. of water contained in a small beaker or conical flask. Diazotise by the addition of a solution of 4 0 g. of sodium nitrite... 

---