Acid persulphuric

Caro s acid, H2SOS. See persulphuric acid, carotene, C4qHs6- M.p. 18 J-J82°C. Carotene... 

Prepared by use of HjOj or by electrolytic oxidation. Persulphuric acids, perborates, are of importance. (Permanganates, perchlorates and periodates are not salts of per-acids.) Organic per-acids are prepared similarly. The... 

Pressures varied from 20 to 1500 Ibf/in (0.14 to 10.5 MPa) and reaction times were of the order of 5-35 hours. Reaction promoters included peroxides and salts of persulphuric and perphosphoric acids. Activators , accelerators and buffering agents were also discussed in the patent. The process of manufacture of Kel-F is understood to be based on this patent. 

Already in 1943 Imperial Chemical Industries (26) applied for a patent on treatments of paper and textile fabrics with vapor of monomeric, readily polymerizable compounds after impregnation with a mixture of persulphuric acid or water-soluble persulphate and of water-soluble oxyacids of sulphur or their salts with reducing properties. In 1951 and in 1952 the same company (27) filed applications on the syn-... 

A soln. of sodium nitrate in oono. sulphuric acid in the absence of air acquires under the action of mercury, copper, or silver an intense blue colour, which gradually fades the colourless soln. contains nitrous oxide. Nitrosulphonic acid forms with a soln. of sulphur dioxide in sulphurio acid a blue soln. from which nitric oxide is quantitatively evolved, 2N02.S03H+S0j+2Hj0 = 2N0+3HsS04. Nitric oxide is absorbed by copper sulphate dissolved in cone, sulphuric acid in the mol, ratio 1 1 at atm. temp, and press. the conception that the dark blue soln. contains the copper salt of nitrosisulphonic acid is strengthened by the observation that hydroxylaminesulphonic acid is oxidized by mono-persulphuric acid in presence of sulphuric acid and a trace of copper to a dark blue compound, whereas hydroxylamine is not similarly affected. 

Orthophosphoric acid does not react with hydrogen dioxide, and there are no signs of the formation of a perphosphoric acid, analogous with persulphuric acid, when soln. of phosphoric acid are electrolyzed. J. Schmidlin and P. Massini,1 and J. d Ans and W. Friederich found the case to be different, however, if phosphorus pentoxide be treated with 30 per cent, hydrogen dioxide at low temp., for when the... 

Later, in 1895, Elbs and Schonherr1 studied the formation of persulphuric acid itself. They found that when the density of the acid employed is less than 1 20 very little persulphuric acid is obtained by electrolysis. Increasing the acid content above this value leads to an increased yield of persulphuric acid, and the maximum quantity is obtained when acid of density 1 35-1 50 is used. 

Caro s acid (H3S06) is formed by the action of water on the persulphuric acid first formed thus —... 

Current efficiency may be increased by adding a substance such as hydrofluoric acid which raises the anode potential, and also by adding sulphurous acid or hydrogen sulphide which destroys Caro s acid but does not affect persulphuric acid. The addition of sulphurous acid to the point of saturation in sulphuric acid of density 1 38 raises the current efficiency to 92 per cent. The addition of hydrochloric acid to the bath has a beneficial effect because it raises the anode potential and also destroys Caro s add, and so removes the harmful depolarising effect of this substance. It has been shown that the concentration of persulphuric acid increases with rise in current density, but the final concentration of Caro s acid is independent of the current density. 

According to a patent claim of the Consortium fur Elek-trochemie an undivided cell may be used, and even without the addition of chromate or fluoride a high yield of ammonium persulphate may be obtained, provided the solution is cooled and a high current density employed (50 amps, per dm.8). Under favourable conditions a 40 per cent, solution of persulphuric acid can be obtained by direct electrolysis of sulphuric acid. 

The oxidation is carried out by means of the so-called Caro s acid (H2S05), which is prepared by reacting sulphuric acid with persulphuric acid salts, or by reacting concentrated hydrogen peroxide with sulphuric acid. 

The 2,4,4 -isomer may also be obtained either by the nitration of azobenzene or of 4,4 -dinitroazoxybenzene with nitric acid sp. gr. 1.51 Klinger and Zuurdeeg [7]). 4,4 -Dinitroazoxybenzene may be obtained by the action of alkalis on p- dinitrobenzene (Lobry de Bruyn [8] Lobry de Bruyn and Blanksma [9] Lobry de Bruyn and Greuns [10]) or by the oxidation of p- nitroaniline with persulphuric acid (Bamberger and Hubner [11]). 

Theoretical principles of the preparation of persulphuric acid and persulphates ... 

Persulphuric acid or persulphates are produced by the oxidation of sulphuric acid or sulphates at an anO de of smooth pure platinum using a high current density. Only smooth platinum can be used for the anodes because no other material displays such a high oxygen overvoltage. 

The liberation of oxygen can, however, be supressed considerably if sulphuric acid is used as the electrolyte, which is anodically oxidized into persulphuric acid. From what has been said about the formation of persulphate ions (see theoretical section) it is clear that the anodic process can be expressed by the following overall equation ... 

It has already been stated that the products of hydrolysis of persulphuric acid are not stable but react with one another under the liberation of oxygen ... 

This process causes depolarization of the anode as it proceeds more easily than reaction (XX-14). Caro s acid is. therefore, harmful not only for causing a loss in active oxygen but also for its depolarizing effect, which lowers the necessary high anode potential whereby current efficiency is decreased. For this reason electrolysis should be carried out under conditions which suppress as much as possible the hydrolysis of persulphuric acid according to equations (XX-15) and (XX-16) and, therefore, the secondary reactions (XX-17) and (XX-18). 

If we disregard the by-products, the products of electrolysis according to the last equation are persulphuric acid and hydrogen. 

The reason for improved current efficiency lies in the fact that mixed solutions of sulphuric acid and sulphates have a lower concentration of free sulphuric acid, so hydrolysis of persulphuric acid and persulphatcs proceeds at a much slower rate which results in considerably less Caro s acid being formed. 

Hydrogen peroxide is obtained from persulphuric acid or persulphate solutions by vacuum distillation. However, before hydrogen peroxide can be distilled,... 

It can be seen from these two equations that the processes are identical with those occurring during electrolysis. However, whilst in electrolysis these reactions were regarded as detrimental they are necessary for the separation of H202 from a solution of persulphuric acid or persnlphates. 

At room temperature persulphuric acid decomposes to hydrogen peroxide at a very low rate. Although a rise in temperature accelerates tho decomposition yet a simultaneous loss of active oxygen is brought about by the following secondary reactions ... 

Because of these reactions the distillation of persulphuric acid and persulphate solutions present a difficult technical problem. First of all, the solutions used for the distillation must be as free as possible of catalytically active substances (such as salts of iron, manganese, copper etc.) as they would considerably promote the decomposition of peroxide. Secondly, satisfactory results require a sufficiently high rate of distillation. A quick heating of the solution to boiling point and a quick removal of the vapours formed from the distillation space means that the time during which the peroxide is in eontact with the persulphuric and Caro s acid and the time of the catalyst action are considerably... 

Fig. 140. Plow sheet of manufacture of hydrogen peroxide from persulphuric acid.

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