Nitrosylsulphuric acid

Nitrosylsulphuric acid, and nitrosyl chloride formed as a result of chloride in the water, can cause corrosion in sulphuric acid and lead-chamber plants. Alloying is not generally beneficial in this instance and some elements (such as copper) can increase the corrosion rate. 

Very feebly basic amines cannot usually be diazotised in dilute acid media and in these instances the reaction has to be carried out in a concentrated acid, normally sulphuric acid. The usual technique is first to dissolve dry sodium nitrite in the concentrated acid, when reaction occurs in two stages (Scheme 4-8), resulting in the formation of nitrosylsulphuric acid (4.5). The nitrosyl ion - nitrous acid equilibrium has been evaluated spectroscopically. In 96% sulphuric acid the 15N-n.m.r. signal is characteristic of the free nitrosyl ion [4]. Reaction (2) of Scheme 4.8 is slow at room temperature and it is desirable to heat the mixture to 70 °C in order to attain equilibrium within a reasonable time. After cooling, the amine is added gradually and after a short time the reaction mixture is poured onto ice, giving an aqueous solution of the diazonium salt [20]. 

Theory of the Action in the Gay-Lussac and Glover Towers.— The gases issuing from the chambers consist mainly of nitrogen dioxide, nitric oxide and atmospheric nitrogen. The two former are dissolved by the sulphuric acid in the Gay-Lussac tower with formation of a solution of nitrosylsulphuric acid in excess of sulphuric acid (see also below) ... 

As the formation of nitrosylsulphuric acid is a reversible process, dilution of the sulphuric acid solution in the Glover tower tends to cause hydrolysis, which is aided by the high temperature the oxides of nitrogen resulting from the decomposition pass on with the sulphur dioxide and excess of air to the chambers, whilst the sulphuric acid descends and issues at the bottom of the tower. 

In addition to the foregoing process, however, the Glover tower actually produces sulphuric acid. This is brought about by interaction of the sulphur dioxide in the burner gases with nitrosylsulphuric acid, as follows ... 

More recently this theory has been modified by the introduction of another intermediate product, namely the violet or blue sulphonitronic acid (see p. 251) which is supposed to precede the formation of the nitrosylsulphuric acid. The series of changes is then represented as follows ... 

Free nitrosylsulphuric acid actually occurs in the lead chambers only under abnormal conditions of working its separation as chamber crystals is most undesirable from the manufacturer s point of view, as not only does it indicate improper regulation of the process, but it also causes the lead walls of the chambers to be attacked unduly. A solution of violet acid is sometimes obtained at the bottom of the Gay-Lussac tower. 

Nitrosulphonic Acid, Nitrosylsulphuric Acid or Nitroso-sulphuric Acid, NQ2.S02.0H.—In 1806, Clement and Desormcs, during the manufacture of sulphuric acid by the lead chamber process, observed the formation of a crystalline solid, to which the names nitrosulphonic acid and nitrosylsulphuric acid were later given the term chamber crystals, however, is still commonly applied to this acid.6 The composition and nature of the acid were first investigated by Weber,7 and by Michaelis and Schumann.8... 

Constitution.—The formation pf nitrosyl chloride or bromide by the action of the acid on sodium chloride or bromide is evidence in favour of the nitrosylsulphuric acid structure, ON.O.SOa.OH. The... 

Formation.—The coloured solution in sulphuric acid is obtainable by passing nitrogen dioxide with air into a saturated solution of sulphur dioxide in diluted sulphuric acid (I 1 by volume) at 0° C. It can also be formed by the addition of sodium hydrogen sulphite to a solution of nitrosulphonic (nitrosylsulphuric) acid, produced by dissolving sodium nitrite in slightly diluted sulphuric acid. These methods depend on the reduction of the nitrosulphonic acid by sulphurous acid or sulphur dioxide 8 the reduction can also be effected by metals, e.g. mercury. 

Nitrosylsulphuric acid, 154, 247. Nitrosylsulphuryl chloride, 200. Nitroxysulphuric acid, 155. 

Aminoanthraquinone, 2 2 kilograms, in concentrated sulphuric acid, is diazotised with nitrosylsulphuric acid. The addition of ice precipitates the diazosulphate, which is removed, dissolved in water and treated with 1 5 kilograms of potassium selenocyanate. The red diazoseleno-cyanate separates out and some nitrogen is evolved. The reaction is completed by warming, whereby an orange precipitate of selenocyanoanthraquinone is obtained. This crystallises from nitrobenzene as yellowish-red needles, M.pt. 249° C. 

In certain instances when negative substituents are present it is necessary to use other acids in place of hydrochloric to bring about diazotisation, e.g., nitrosylsulphuric acid, in presence of cone, sulphuric (J. pr., 56, 48), in glacial acetic (J. C. S., 1933,1620), in phosphoric acid (Am. Soc., 1933, 4531). 

As indicated in connection with iodine tetroxide, N. A. E. Millon observed the formation of what he considered to be nitroso-iodic acid, and H. Kammorer what he considered to be iodine dinitrosyl tetroxide, I204(N0)8, or maybe O I.O.NO, by treating iodine with nitric acid, or nitrosylsulphuric acid. The yellow powder was considered by H. Kappeler to be iodine nitrate, T.NOj, vide 2. 19, 9. E. Briner said that mixtures of nitric and hydriodie acids do not form a univariant system like stabilized aqua regia, for the iodine produced as a result of the primary reaction is oxidized to iodic acid, with the evolution of nitric oxide. 

J. Biehringer and W. Borsum suggested that nitrosylsulphuric acid exists in two tautomeric forms, H0.S02.0. N0 + H0. S02.N02, which are in equilibrium in cone, sulphuric acid soln. and in the molten state. In support of this, they found that in some cases it can react simultaneously as two different acids, for, when a soln. of dimethylaniline in cone, sulphuric acid is slowly treated with the requisite amount of sodium nitrite, both p-nitrodimethylaniline and p-nitroso-dimethylaniline are produced, the former represents the nitrosyl-acid and the latter the nitroxyl-acid. At 10° to 15°, the yields are respectively 8-33 and 7+5... 

Pinck [88] studied the nitrating action of nitrogen dioxide in a sulphuric acid solution. According to this author, the nitrating action of the solution proceeds as follows, from each N204 molecule with the formation of one molecule of HN03 and one of nitrosylsulphuric acid ... 

Benzene activated with sulphuric acid would add on to N204 which, according to Battegay, has the structure of nitrosyl nitrate N02.0N0. An addition product was thought to be formed which, in the presence of an excess of sulphuric acid, would decompose to yield a nitro compound and nitrosylsulphuric acid. 

Recently Kobe Mid Lakemeyer [17] drew attention to the fact that nitrating mixtures used for mononitration of toluene prepared spent acid from trinitration contain 14-17 wt. % of nitrosylsulphuric acid. They investigated the influence of nitrosylsulphuric acid, S02(OH)ONO, on the rate of mononitration of toluene. The rate at 35°C is at a maximum at ca. 4.0 mole % of nitrosylsulphuric acid. 

According to Kobe and Lakemeyer [17], the nitrosylsulphuric acid represents about 17 wt. % of the total amount of spent acid from the trinitration. Its presence would subsequently considerably affect the process of the nitration of toluene to the mononitro-product, since it makes 14-17 wt. % of the acid used for the mononitration. 

In a German method, applied at the Kriimmel factory, the crude acid TNT, after it has been washed free from nitrosylsulphuric acid, is washed several times with water at a temperature of 90°C in brick washing vats lined with sheet lead, or in stainless steel tanks. The deacidification is finally followed by neutralization with an NaHC03 solution of concentration about 1%. The product obtained in this stage has a freezing point of 78.8-78.3°C. 

The acid llowing from the cr> stallizcr contains ca. 5.3% dissolved TNT and ca. 9.7% HNOj the rest being sulphuric acid. SOj and nitrosylsulphuric acid. It passes to the first (hot) crystallizer, after the draining of TNT. it is washed with 70% sulphuric acid, followed by washing with water. 

Nitrating acid wcis prepared by mixing the constituents in a stainless steel bucket submerged in a water bath, the temperature being maintained below 20 C to reduce the possibility of forming nitrosylsulphuric acid. 

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