Nitrite solution

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. 

Dissolve 5 g. (5 ml.) of aniline in 50 ml. of warm dilute sulphuric acid in a conical flask and add 50 ml. of water. 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 falls to 5°. Dissolve 4-5 g. of powdered sodium nitrite in 20 ml. of water, and add this solution in small quantities (about 2-3 ml. at a time) to the cold aniline sulphate solution. Keep tne latter well shaken and maintain the temperature at about 5° (see p. 183). When all the sodium nitrite solution has been added, transfer about 5 ml. of the cold solution to a test-tube for each of the following reactions. The remainder of the diazonium hydrogen sulphate solution must be kept in ice-water until required, and then when all the reactions have been carried out, the solution should be poured down the sink. 

Prepare two solutions, one containing i g. of diphenylamine in 8 ml. of warm ethanol, and the other containing 0-5 g. of sodium nitrite in i ml. of water, and cool each solution in ice-water until the temperature falls to 5°. Now add o 8 ml. of concentrated hydrochloric acid steadily with stirring to the diphenylamine solution, and then without delay (otherwise diphenylamine hydrochloride may crystallise out) pour the sodium nitrite solution rapidly into the weil-stirred mixture. The temperature rises at once and the diphenylnitrosoamine rapidly crystallises out. Allow the mixture to stand in the ice-water tor 15 minutes, and then filter off the crystals at the pump, drain thoroughly, wash with water to remove sodium chloride, and then drain again. Recrystallise from methylated spirit. Diphenylnitrosoamine is thus obtained as very pale yellow crystals, m.p. 67 68° yield, 0 9-1 o g. 

The mixed bases are dissolved in dilute hydrochloric acid and sodium nitrite solution added. The aniline is thus diazotised and, if the mixture is subsequently boiled, converted into phenol. The solution is then made alkaline and steam-distilled, the quinoline passing over, while the phenol remains behind in the alkaline solution. 

Azo-dye formation. Dissolve 2-3 drops of aniline in 1 ml. of cone. HCl and add 3 ml. of water. Shaike to dissolve any hydrochloride which may have separated and cool in ice. Add a few drops of 20% sodium nitrite solution. Add this cold diazonium solution to a cold solution of the phenol in an excess of aqueous NaOH solution. Solutions or precipitates of azo-dyes ranging in colour from orange through scarlet to dark red, according to the phenol used, are obtained. Note in particular that i-naphthol gives a brownish-red, 2-naphthol a scarlet precipitate. Catechol decomposes. 

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. 

Formation of nitrosaminey RgN NO. (a) From monomethylaniline. Dissolve I ml. of monomethylaniline in about 3 ml. of dil. HCl and add sodium nitrite solution gradually with shaking until the yellow oil separates out at the bottom of the solution. Transfer completely to a smdl separating-funnel, add about 20 ml. of ether and sh e. Run off the lower layer and wash the ethereal extract first with water, then with dil. NaOH solution, and finally with w ter to free it completely from nitrous acid. Evaporate the ether in a basin over a previously warmed water-bath, in a fume cupboard with no flames near. Apply Liebermann s reaction to the residual oil (p. 340). 

Mercuric nitrite reaction (Millon s reaction). Dissolve a very small crystal of tyrosine in i ml. of water, add 1-2 drops of mercuric nitrate solution, and I drop of dil. HjSO, and then boil. Cool, add i drop of sodium nitrite solution and warm again a red coloration is obtained. 

Diazotisation. Dissolve 0 2 g. of anthranilic acid in about 4 ml. of dil. HCl and cool in ice-water. To this solution, add slowly about I ml. of cold 20% sodium nitrite. solution and divide the cold diazonium solution thus prepared into two portions A and B. 

Diazotisation. Dissolve 0 2 g. of the substance in about 5 ml. of dil. HCl, warming if necessary. Cool in ice-water and add sodium nitrite solution drop by drop the end of the diazotisation is marked by the complete decolorisation of the solution. Pour the diazonium solution into a cold solution of 2-naphthol in a considerable excess of NaOH solution a brilliant red dye is produced. 

Dissolve 20 g, (19 -6 ml.) of anihne in a mixture of 55 ml. of concentrated hydrochloric acid (1) and 55 ml. of water contained in a 350 ml, conical flask. Place a thermometer in the solution and immerse the flask in a bath of crushed ice (2) cool until the temperature of the stirred solution falls below 5°, Dissolve 16 g. of sodium nitrite in 75 ml. of water and chUl the solution by immersion in the ice bath add the sodium nitrite solution (3) in small volumes (2-3 ml. at a time) to the cold anihne hydrochloride solution, and keep the latter weh stirred with the thermometer. Heat is evolved by the reaction. The temperature should not be allowed to rise above 10° (add a few grams of ice to the reaction mixture if necessary) otherwise appreciable decomposition of the diazonium compound and of nitrous acid wih occur. Add the last 5 per cent, of the sodium nitrite solution more slowly (say, about 1 ml. at a time) and, after stirring for 3-4 minutes, test a drop of the solution diluted with 3-4 drops of water with potassium iodide - starch paper (4) if no immediate blue colour... 

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. 

It is advisable to test the potassium iodide - starch pap>er with acidified sodium nitrite solution the commercial test paper is, particularly if it has been kept for a considerable period, sometimes almost useless. The solution must contain an excess of acid at all times, i.e., it must give a blue colour on Congo rod paper. 

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). 

The sodium nitrite solution is conveniently added from a dropping funnel it is recommended, particularly for preparations on a larger scale, that the tip of the stem of the funnel dip well below the surface of the liquid. 

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... 

Place 130 ml. of concentrated hj drochloric acid in a 1 - 5 litre round-bottomed flask, equipped ith a mechanical stirrer and immersed in a freezing mixture of ice and salt. Start the stirrer and, when the temperature has fallen to about 0°, add 60 g. of finely-crushed ice (1), run in 47 5 g. (46 5 ml.) of pure aniline during about 5 minutes, and then add another 60 g. of crushed ice. Dissolve 35 g. of sodium nitrite in 75 ml. of water, cool to 0-3°, and run in the cold solution from a separatory funnel, the stem of which reaches nearly to the bottom of the flask. During the addition of the nitrite solution (ca. 20 minutes), stir vigorously and keep the temperature as near 0° as possible by the frequent addition of crushed ice. There should be a slight excess of nitrous acid (potassium iodide-starch paper test) at the end of 10 minutes after the last portion of nitrite is added. 

Dissolve 1 g. of the secondary amine in 3-5 ml. of dilute hydrochloric acid or of alcohol (in the latter case, add 1 ml. of concentrated hydrochloric acid). Cool to about 5° and add 4-5 ml. of 10 per cent, sodium nitrite solution, and allow to stand for 5 minutes. Add 10 ml. of water, transfer to a small separatory funnel and extract the oil with about 20 ml. of ether. Wash the ethereal extract successively with water, dilute sodium hydroxide solution and water. Remove the ether on a previously warmed water bath no flames should be present in the vicinity. Apply Liebermann s nitroso reaction to the residual oil or solid thus. Place 1 drop or 0 01-0 02 g. of the nitroso compovmd in a dry test-tube, add 0 05 g. of phenol and warm together for 20 seconds cool, and add 1 ml. of concentrated sulphuric acid. An intense green (or greenish-blue) colouration will be developed, which changes to pale red upon pouring into 30-50 ml. of cold water the colour becomes deep blue or green upon adding excess of sodium hydroxide solution. 

Chlorodiphenyl. Diazotise 32 g. of o-chloroaniline (Section IV,34) in the presence of 40 ml. of concentrated hydrochloric acid and 22 -5 ml. of water in the usual manner (compare Section IV,61) with concentrated sodium nitrite solution. Transfer the cold, filtered diazonium solution to a 1 5 htre bolt-head flask surrounded by ice water, introduce 500 ml. of cold benzene, stir vigorously, and add a solution of 80 g. of sodium acetate trihydrate in 200 ml. of water dropwise, maintaining the temperature at 5-10°. Continue the stirring for 48 hours after the first 3 hours, allow the reaction to proceed at room temperature. Separate the benzene layer, wash it with water, and remove the benzene by distillation at atmospheric pressure distil the residue under reduced pressure and collect the 2-chlorodiphenyl at 150-155°/10 mm. The yield is 18 g. Recrystalliae from aqueous ethanol m.p. 34°. 

Meihylamine hydrochloride method. Place 100 g. of 24 per cent, methyl-amine solution (6) in a tared 500 ml. flask and add concentrated hydrochloric acid (about 78 ml.) until the solution is acid to methyl red. Add water to bring the total weight to 250 g., then introduce lSO g. of urea, and boil the solution gently under reflux for two and three-quarter hours, and then vigorously for 15 minutes. Cool the solution to room temperature, dissolve 55 g. of 95 per cent, sodium nitrite in it, and cool to 0°. Prepare a mixture of 300 g. of crushed ice and 50 g. of concentrated sulphuric acid in a 1500 ml. beaker surrounded by a bath of ice and salt, and add the cold methylurea - nitrite solution slowly and with mechanical stirring and at such a rate (about 1 hour) that the temperature does not rise above 0°. It is recommended that the stem of the funnel containii the methylurea - nitrite solution dip below the surface of the acid solution. The nitrosomethylurea rises to the surface as a crystalline foamy precipitate. Filter at once at the pump, and drain well. Stir the crystals into a paste with about 50 ml. of cold water, suck as dry as possible, and dry in a vacuum desiccator to constant weight. The yield is 55 g. (5). 

This solution may also be employed in the test for bromine. If iodine has been found, add small amounts of sodium nitrite solution, warm shghtly and shake with fresh 1 ml. portions of carbon tetrachloride until the last extract is colourless boil the acid solution until no more nitrous fumes are evolved and cool. If iodine is absent, use 1 ml. of the fusion solution which has been strongly acidified with glacial acetic acid. Add a small amount of lead dioxide, place a strip of fluorescein paper across the mouth of the tube, and warm the solution. If bromine is present, it will colour the test paper rose-pink (eosin). 

Routine Run. - A second experiment was then carried out using the same quantities of ethyl sulphate as above. The recovered nitrite solution (lower layer) from the first run was concentrated by adding approximately 16 g. of sodium nitrite per 160 c.c. of solution. Yield, 185 g. (46%, or allowing for recovered ethyl sulphate, 65%)."... 

The assay determination of sulfamic acid is made by titration of an accurately prepared sulfamic acid solution using sodium nitrite solution and an external potassium iodide starch-paste indicator. It is based on the reaction... 

To a cold mixture of 800 cc. of 95 per cent ethyl alcohol and 200 cc. of concentrated sulfuric acid (Note i) in a 5-I. round-bottom flask, provided with an efficient mechanical stirrer, is added 250 g. (1.33 moles) of crude 3-bromo-4-aminotoluene (p. 8). The solution is stirred and cooled to 10° and a solution of 148 g. (2.05 moles) of d.s.p. sodium nitrite in 260 cc. of water is added from a separatory funnel. During this addition, the temperature of the mixture must not be allowed to rise above 10°. After all of the nitrite solution has been added, the mixture is stirred twenty minutes longer to complete the diazotization. 

Owing to the instability of sodium nitrite solutions, the addition of the solid salt is preferred. 

Note Note that the diazotization of primary aromatic amines can also be achieved by placing the chromatogram for 3 — 5 min in a twin-trough chamber containing nitrous fumes (fume cupboard ). The fumes are produced in the empty trough of the chamber by addition of 25% hydrochloric acid to a 20% sodium nitrite solution [2, 4], iV-(l-Naphthyl)ethylenediamine can be replaced in the reagent by a- or -naphthol [10, 14], but this reduces the sensitivity of detection [2]. Spray solutions Ila and lib can also be used as dipping solutions. 

Detection and result The chromatogram was freed from mobile phase (10 min in a stream of warm air) and placed for 10 min in the empty half of a twin-trough chamber in whose second half nitrous fumes were being generated by the addition of 10 drops 37% hydrochloric acid to 5 ml 20% aqueous sodium nitrite solution. After the nitrous fumes had cleared (3 —5 min in air, fume cupboard ) the chromatogram was immersed in solution Ila for 1 s and dried in a stream of cold air. 

Reacimj.—Dissolve a few ciystals in water, acidify with dilute hydrochloric acid, and add a drop of sodium nitrite solution. A deep biown solution (Bismarck brown) is obtained. See Appendix, p. 279. 

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