Nitrous fumes

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. 

The final products are then sulphuric acid, nitrogen oxide and oxygen the two latter react and the cycle goes on. Theoretically therefore, the nitrous fumes are never used up. In practice, however, some slight replacement is needed and this is achieved by adding a little concentrated nitric acid to the mixture in the Glover tower ... 

This preparation must be performed in a fume-cupboard, because nitrous fumes are evolved during the nitration. A ground-glass flask and air condenser (Fig. 22(a) and (c), p. 43) should preferably be used. 

For this purpose, the usual oxidising agent is nitric acid, which in these circum stances (i.e., in the absence of sulphuric acid) does not nitrate the benzene ring. Owing to the nitrous fumes formed by the reduction of the nitric acid, the experiment should be performed in a fume upboard. 

Method 2. This preparation should be carried out in the fume cupboard since nitrous fumes are evolved. Place 62 g. of benzoic acid and 300 ml. of concentrated sulphuric acid in a 2-litre roimd-bottomed flask, warm on a water bath with shaldng until the benzoic acid dissolves, and cool to 20°. Add 100 ml. of fuming nitric acid (sp. gr. 1-54) in portions... 

Nitrophthalic acid. Equip a 1500 ml. three-necked flask, supported on a water or steam bath, with a dropping funnel, a mechanical stirrer and a thermometer the neck through which the stirrer passes should be open and the stirrer should be cormected by means of a belt to the motor (nitrous fumes are evolved in the subsequent reaction and these would damage the motor if supported directly over the reaction... 

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). 

Nitric acid Copper, brass any heavy metals Nitrogen dioxide (nitrous fumes)... 

Polycyclic aromatic hydrocarbons (PAH) Apply sample solution and dry. Place TLX2 plate for 20 min in a twin-trough chamber containing phosphorus pentoxide to which 2 to 3 ml cone, nitric acid have been added. PAH nitrated by nitrous fumes. [20]... 

Phenols Apply sample solution, dry, expose to nitrous fumes. [56]... 

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. 

The chloiallndrate is melted in a distilling flask (250 c.c.)and the fii.ninit nitiic and added.The mixture is heated caiefully o et a small flame until the leaction sets in. Aftei a few minutes led fumes are evolved, consi.stiny mainly of nitiogen tetio ide. The leaction proceeds without the application of heat, and is complete when, on warming- the liquid, nitrous fumes cease to come off. The product is now distilled below... 

The lDcii70in and nltiic acid are heated on the water-bath with an. >ir condenser, the flask being occasionally shaken. Nitrous fumes arc evolved, and the crystals of benzoin are converted into a yellow oil, which, after two hours heating, is free from un-(hanged benzoin. The contents of the flask are now poured into water, and the yellow crystalline deposit separated by filtration, washed with water, and recrystallised fiom alcohol. Yield, 10—12 grams. 

On the industrial scale, impure NaN02 is made by absorbing nitrous fumes in aqueous alkali or carbonate solutions and then reciystallizing the product ... 

It is prepared by passing nitrous fumes into ice-cold pinene. It forms an acetate,. COCHg, which has a marked lavender odour. 

Pinenyl Acetate.—By passing nitrous fumes into well-cooled pinene and steam-distilling the reaction product, an alcohol, pinenol, is obtained. It has the formula CjgHjjOH. It can be acetylated, and the resulting acetate has the formula C,gH,5—OOCCHg. It has an odour resembling that of lavender oil. It boils at 150°. at a pressure of 40 mm. 

Salpeter-ather, m. nitric ether (ethyl nitrate), -bakterien, n.pl. nitrifying bacteria, -bil-dung, /. nitrification, -blumen, f.pl. niter efflorescence, -damp/, -dupst, m. nitrous fumes, -erde, /. nitrous earth, -erzeugung, /. niter production nitrification. 

Stickwetter, n.pl. (Mining) foul air, choke damp, after-damp, nitrous fumes. 

The inhalation of concns of 200 to 700ppm may be fatal after even very short exposure (Ref 11). Also see under Nitrous Fumes in this Vol... 

Nitrogen tetroxide is one of the most insidious gases in terms of human toxicity. Inflammation of the lungs may cause only slight pain or pass unnoticed, but the resulting edema several days later may cause death. lOOppm is dangerous for even a short exposure, and 200 ppm may be fatal (Ref 25). Also see under Nitrous Fumes in this Vol... 

Nitrous Fumes. This term includes any nitrogen oxide fumes produced in the manuf of nitric... 

Exposure to nitrous fumes is always potentially serious, and persons so exposed should be kept under close observation for at least 48 hours (Refs 1, 2, 3, 5 6)... 

The thoroughness and extent of the work of Griess in this field probably account for the fact that Mene (1861) is rarely mentioned in this connection. Independently of Griess, and possibly even before him, Mene obtained 1,3-diphenyltriazene through the action of nitrous fumes on aniline. 

For these reasons there are limits to the extent to which the acid concentration can be increased gradually as the basicity of the amines decreases. Nevertheless, diazotization can be carried out without difficulty in 90-96% sulfuric acid. It has already been mentioned that nitrous fumes are given off as soon as nitrite is added to sulfuric acid of lower concentration, but solid sodium nitrite can be dissolved in 90-96% sulfuric acid at 0-10°C smoothly and without evolution of gas. Nitrosylsulfuric acid, N0+HS04, is formed. Directions for the preparation of 2 m nitrosylsulfuric acid are given by Fierz-David and Blangey (1952, p. 244), but sodium hydrogen sulfate crystallizes after some time from acid of this strength so that it is best to prepare a stock solution of 1 m sodium nitrite in 96% sulfuric acid, which is quite stable at room temperature. 

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