Nitrogen sulphuric acid

Nitric acid5 undergoes reduction by sulphurous acid less readily than nitrous acid, the product in each case being sulphuric acid with nitrous or nitric oxide it is possible that nitrogen-sulphur acids such as nitro-sulphonic acid are intermediately produced (see p. 248). Nitric oxide can be reduced slowly to nitrous oxide by sulphurous acid, but no further.7... 

Nitric Acid.—-The commercial cone, acid generally contains about 70% HN03. Fuming nitric acid (see p. 512) containing about 95% HN03 (D. 1-5) is available commercially. Usual impurities oxides of nitrogen, sulphuric acid, hydrochloric acid, chlorine and iodine. 

The methods of testing are giv< n in Vol. I., p. 489. These include the total acidity, lower oxides of nitrogen, sulphuric acid, chlorine, iodine and mineral matter. T he lower oxides are usually restricted... 

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. 

Ammonia may be estimated by dissolving the gas in a known volume of standard acid and then back-titrating the excess acid. In a method widely used for the determination of basic nitrogen in organic substances (the Kjeldahl method), the nitrogenous material is converted into ammonium sulphate by heating with concentrated sulphuric acid. The ammonia is then driven off by the action of alkali and absorbed in standard acid. 

The reduction of a nitrate, for example potassium nitrate, by iron(ll) sulphate in the presence of concentrated sulphuric acid gives reasonably pure nitrogen monoxide. The mixture is warmed and at this temperature the nitrogen monoxide produced does not combine with uncharged iron(II) sulphate (see below). 

Reduction products vary depending on the reducing agent, for example dinitrogen oxide is obtained with sulphurous acid, nitrogen is obtained when the gas is passed over heated metals (e.g. copper and iron) and ammonia is produced when the gas reacts with aqueous chromiumfll) salts. 

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 ... 

By their oxidising action heating with copper and concen trated sulphuric acid yields brown fumes of nitrogen dioxide. 

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 ... 

When concentrated sulphuric acid is added to a nitrate in the presence of aqueous iron(II) sulphate, the nitrogen oxide liberated forms a brown complex [Fe(H20)5N0] which appears as a brown ring at the acid-aqueous interface (test for a nitrate, p 243). 

Dissolve ca. 0 2 g. of product (I) in cold ethanol, and add with shaking 1-2 drops of dilute sulphuric acid. A deep purple coloration appears at once. This shows that salt formation has occurred on the quinoline nitrogen atom to form the cation (Ha), which will form a resonance hybrid with the quinonoid form tils). [Note that the forms (IIa) and (11b) differ only in electron position, and they are not therefore tautomeric.] If, hoAvever, salt formation had occurred on the dimethylaniino group to give the cation (III), thrs charge separiition could not occur, and the deep colour would be absent. 

Now add more dilute sulphuric acid drop by drop the colour almost completely fades, as salt formation occurs on both nitrogen atoms with suppression of the resonance hybrid formation. 

Digestion. 20-25 mg. of the substance whose nitrogen content is to be estimated are weighed out in a stoppered weighing-tube and then transferred to the flask L that has been previously dried in an oven at izo C. With care, the substance may be transferred directly into the bulb of the flask without any adhering to the sides. If any material sticks on the way down, the flask should be tapped gently to cause the substance to fall to the bottom. 2 G. of the catalyst mixture (32 g. of potassium sulphate, 5 g. of mercury sulphate and ig. of selenium powder, well mixed) are added and 3 ml. of A.R. cone, sulphuric acid are measured out carefully and poured into the digestion... 

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. 

Acetanilide from acetophenone. Dissolve 12 g. of acetophenone in 100 ml. of glacial acetic acid containing 10 g. of concentrated sulphuric acid. To the stirred solution at 60-70°, add 9 8 g. of sodium azide in small portions at such a rate that the temperature does not rise above 70°. Stir the mixture with gentle heating until the evolution of nitrogen subsides (2-3 hours) and then allow to stand overnight at room temperature. Pour the reaction mixture on to 300 g. of crushed ice, filter the solid product, wash it with water and dry at 100°. The yield of crude acetanilide, m.p. 111-112°, is 13 g. Recrystallisation from water raises the m.p. to 114°. 

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... 

If sulphur is present, a black precipitate of ferrous sulphide is obtained when the ferrous sulphate crystals dissolve. Boil the mixture for about 30 seconds, and acidify with dilute sulphuric acid the ferrous sulphide dissolves and a precipitate of Prussian blue forms if nitrogen is present. 

Nitrogen. Treat one portion with 1-2 ml. of 5 per cent, sodium hydroxide solution and 0 1 g. of powdered ferrous sidphate. Boil for 1 minute and cool. Cautiously acidify with dilute sulphuric acid (carbon dioxide is evolved). A precipitate of Prussian blue indicates that nitrogen is present. 

The first quantitative studies of the nitration of quinoline, isoquinoline, and cinnoline were made by Dewar and Maitlis, who measured isomer proportions and also, by competition, the relative rates of nitration of quinoline and isoquinoline (1 24-5). Subsequently, extensive kinetic studies were reported for all three of these heterocycles and their methyl quaternary derivatives (table 10.3). The usual criteria established that over the range 77-99 % sulphuric acid at 25 °C quinoline reacts as its cation (i), and the same is true for isoquinoline in 71-84% sulphuric acid at 25 °C and 67-73 % sulphuric acid at 80 °C ( 8.2 tables 8.1, 8.3). Cinnoline reacts as the 2-cinnolinium cation (nia) in 76-83% sulphuric acid at 80 °C (see table 8.1). All of these cations are strongly deactivated. Approximate partial rate factors of /j = 9-ox io and /g = i-o X io have been estimated for isoquinolinium. The unproto-nated nitrogen atom of the 2-cinnolinium (ina) and 2-methylcinno-linium (iiiA) cations causes them to react 287 and 200 more slowly than the related 2-isoquinolinium (iia) and 2-methylisoquinolinium (iii)... 

The nitration bath normally contains sulphuric acid as a condensing agent and a typical bath for producing a cellulose nitrate with a nitrogen content of 11 % would be... 

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