Nitric acid Nitrogen

The process for the production of nitrobenzene from benzene involves the use of mixed acid (Fig. 1), but there are other useful nitrating agents, e.g., inorganic nitrates, oxides of nitrogen, nitric acid plus acetic anhydride, and nitric acid plus phosphoric acid. In fact, the presence of sulfuric acid in quantity is vital to the success of the nitration because it increases the solubility of the hydrocarbon in the reaction mix, thus speeding up the reaction, and promotes the ionization of the nitric acid to give the nitronium ion (N02+), which is the nitrating species. Absorption of water by sulfuric acid favors the nitration reaction and shifts the reaction equilibrium to the product. 

Provided. Primary standard AgN03, ferric alum indicator [KFe(S04)2 12 H2O, saturated solution], 6 M HNO3 (free of oxides of nitrogen). Nitric acid free from lower oxides of nitrogen should be colorless and can be prepared, if necessary, by boiling 1 1 HNO3 until NO2 is expelled. 

Oxidized nitrogen. Nitric acid produces passivity with Al, but in the presence of small amounts of some other ions, e.g., Hg, it dissolves rapidly, forming NO in concentrated HNO3, and NH4NO3 in the dilute. 

Oxidized nitrogen. Nitric acid (initiated by some HNO2) or aqua regia dissolves Bi well. At 65 °C the reaction with HNO3 is essentially ... 

Again, nitric acid readily dissolves lead but is unable to oxidise lead beyond the oxidation state -P 2. The reduction products of the nitric acid vary with the concentration of acid used, and a number of nitrogen oxides are usually obtained. Warm dilute nitric acid gives mainly nitrogen oxide, NO. 

Concentrated sulphuric acid and nitric acid—powerful oxidising agents—attack all the elements except nitrogen, particularly when the acids are warm. The products obtained reflect changes in stability of the oxidation states V and III of the Group V elements. 

In the presence of catalyst, usually platinum, ammonia is oxidised by oxygen (and air) to nitrogen oxide. NO. This reaction, used to obtain nitric acid from ammonia (p. 238), can be demonstrated in the laboratory using the apparatus shown in Figure 9.4 the oxygen rate should be slow. 

Uses of ammonia and ammonium compounds. Most of the ammonia produced is used in the manufaeture of nitrogenous fertilisers such as ammonium sulphate. Other uses include nitric acid and synthetic fibre and plastic manufacture. 

The reaction between copper and nitric acid, 1 part concentrated acid and 1 part water, gives impure nitrogen monoxide ... 

Industrially nitrogen monoxide is prepared by the catalytic oxidation of ammonia as an intermediate in the manufacture of nitric acid (p. 238). The molecule of nitrogen monoxide contains an odd number of electrons and can be represented as... 

Nitrogen dioxide dissolves in water to give a mixture of nitrous and nitric acids ... 

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 ... 

Non-metals — These are often oxidised to the corresponding oxoacid, and nitrogen oxide is formed. For example, sulphur gives sulphuric acid with cold concentrated nitric acid ... 

Nitrous acid is unstable, decomposing to give nitric acid and evolving nitrogen oxide ... 

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 ... 

With more concentrated nitric acid, oxides of nitrogen are formed. 

Equip a 500 ml. three necked flask with a reflux condenser, a mercury-sealed mechanical stirrer and separator funnel, and support it on a water bath. Attach an absorption device (Fig. II, 8, 1, c) to the top of the condenser (1). Place 134 g. (152 ml.) of A.R, benzene and 127 g. of iodine in the flask, and heat the water bath to about 50° add 92 ml. of fuming nitric acid, sp. gr. 1-50, slowly from the separatory funnel during 30 minutes. Oxides of nitrogen are evolved in quantity. The temperature rises slowly without the application of heat until the mixture boils gently. When all the nitric acid has been introduced, reflux the mixture gently for 15 minutes. If iodine is still present, add more nitric acid to the warm solution until the purple colour (due to iodine) changes to brownish-red. 

Method 1. Place 20 g. of crude benzoin (preceding Section) and 100 ml. of concentrated nitric acid in a 250 ml. round-bottomed flask. Heat on a boiling water bath (in the fume cupboard) with occasional shaking until the evolution of oxides of nitrogen has ceased (about 1 -5 hours). Pour the reaction mixture into 300-400 ml. of cold water contained in a beaker, stir well until the oil crystallises completely as a yellow solid. Filter the crude benzil at the pump, and wash it thoroughly with water to remove the nitric acid. RecrystaUise from alcohol or methylated spirit (about 2-5 ml. per gram). The yield of pure benzil, m.p. 94-96°, is 19 g. 

Add, with stirring, a solution of 6 8 g. of the fiis-diazo ketone in 100 ml. of warm dioxan to a suspension of 7 0 g. of freshly precipitated silver oxide in 250 ml. of water containing 11 g. of sodium thiosulphate at 75°. A brisk evolution of nitrogen occurs after 1 5 hours at 75°, filter the liquid from the black silver residue. Acidify the almost colourless filtrate with nitric acid and extract the gelatinous precipitate with ether. Evaporate the dried ethereal extract the residue of crude decane-1 10-dicarboxylic acid weighs 4 -5 g. and melts at 116-117°. RecrystaUisation from 20 per cent, aqueous acetic acid raises the m.p. to 127-128°. 

Nitrogen and sulphur absent, (i) If only one halogen is present, acidify with dilute nitric acid and add excess of silver nitrate solution. A precipitate indicates the presence of a halogen. Decant the mother liquor and treat the precipitate with dilute aqueous ammonia solution If the precipitate is white and readily soluble in the ammonia solution, chlorine is present if it is pale yellow and difficultly soluble, bromine is present if it is yellow and insoluble, then iodine is indicated. Iodine and bromine should be confirmed by the tests given below. 

Nitrogen and sulphur present. Just acidify 2-3 ml. of the fusion solution with dilute nitric acid, and evaporate to half the original volume in order to expel hydrogen cyanide and/or hydrogen sulphide which may be present. Dilute with an equal volume of water. If only one halogen is present, proceed as in tests (i) or (iii). If one or more halogens may be present, use tests (ii), (iii) or (iv). 

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