Pyrosulphate

The most recent work indicates that in anhydrous sulphuric acid the above conversion is complete. The slightly modified absorption band in oleum arises from the hydrogen pyrosulphate ion formed in the following way ... 

Porcelain crucibles are very frequently utilised for igniting precipitates and heating small quantities of solids because of their cheapness and their ability to withstand high temperatures without appreciable change. Some reactions, such as fusion with sodium carbonate or other alkaline substances, and also evaporations with hydrofluoric acid, cannot be carried out in porcelain crucibles owing to the resultant chemical attack. A slight attack of the porcelain also takes place with pyrosulphate fusions. 

Substances which are insoluble or only partially soluble in acids are brought into solution by fusion with the appropriate reagent. The most commonly used fusion reagents, or fluxes as they are called, are anhydrous sodium carbonate, either alone or, less frequently, mixed with potassium nitrate or sodium peroxide potassium pyrosulphate, or sodium pyrosulphate sodium peroxide sodium hydroxide or potassium hydroxide. Anhydrous lithium metaborate has found favour as a flux, especially for materials containing silica 12 when the resulting fused mass is dissolved in dilute acids, no separation of silica takes place as it does when a sodium carbonate melt is similarly treated. Other advantages claimed for lithium metaborate are the following. 

Naturally, the flux employed will depend upon the nature of the insoluble substance. Thus acidic materials are attacked by basic fluxes (carbonates, hydroxides, metaborates), whilst basic materials are attacked by acidic fluxes (pyroborates, pyrosulphates, and acid fluorides). In some instances an oxidising medium is useful, in which case sodium peroxide or sodium carbonate mixed with sodium peroxide or potassium nitrate may be used. The vessel in which fusion is effected must be carefully chosen platinum crucibles are employed for... 

NH SC - NH2S03H + H20 which then reacted to form the pyrosulphate... 

Flood, H. Forland, T. (1947b). The acidic and basic properties of oxides. II. The thermal decomposition of pyrosulphates. Acta Chemica Scandinavica, 1, 781-9. 

Limited decomposition of the sulphate and extensive melamine condensation overlap in this second step with condensation of sulphuric acid residues to pyrosulphuric structures. This is shown by water evolution and appearance of typical absorptions of pyrosulphate... 

Ammonia is evolved here in the condensation process of melamine to melam whereas the respective ammonium salts are evolved in the case of the hydrobromide and nitrate. Reactions 9 and 9b show that ammonia should be neutralised by pyrosulphuric acid groups. In TG we have found that diammonium pyrosulphate eliminates ammonia above 350 C, with however complete decomposition ... 

Figure 11. IR of anhydrous melamine sulphate (A) and of residue at 400 C (B) likely melam pyrosulphate.

In the following third step (450-520 0), (Figure 10) the melam pyrosulphate is further condensed to melon with decomposition of the pyrosulphuric structure as shown by disappearance of typical absorptions of pyrosulphate or sulphate in the IR of the melon left as a residue. This last decomposes then above 520 0 (4th step). The proposed degradation scheme for the sulphate is ... 

The soil samples were first heated to fumes with a mixture of nitric and sulphuric acids. This method gave appreciably higher arsenic recoveries (95-102%) than fusion with potassium pyrosulphate and was considerably more rapid than fusion with a mixture of nitric and perchloric acids. 

Fusion with a flux such as sodium hydroxide, potassium bifluoride potassium pyrosulphate has been used extensively in the water industry. 

Sulphuric acid catalysts are not truly heterogeneous catalysts but so-called supported liquid phase (SLP) catalysts, where the oxidation of S02 takes place as a homogeneous reaction in a liquid film covering the internal surface of the support material [2], This was proposed already in 1940 by Frazer and Kirkpatrick [6], who found that the promoting action of the common alkali metals was due to their ability to form relatively low-melting pyrosulphates, which dissolve vanadium oxides, e.g. for potassium... 

The silica carrier of a sulphuric acid catalyst, which has a relatively low surface area, serves as an inert support for the melt. It must be chemically resistant to the very corrosive pyrosulphate melt and the pore structure of the carrier should be designed for optimum melt distribution and minimum pore diffusion restriction. Diatomaceous earth or synthetic silica may be used as the silica raw material for carrier production. The diatomaceous earth, which is also referred to as diatomite or kieselguhr, is a siliceous, sedimentary rock consisting principally of the fossilised skeletal remains of the diatom, which is a unicellular aquatic plant related to the algae. The supports made from diatomaceous earth, which may be pretreated by calcination or flux-calcination, exhibit bimodal pore size distributions due to the microstructure of the skeletons, cf. Fig. 5. 

Sodium hydro-pyrosulphate, or sodium hydrogen anhydro-sulphate. NaHS20,... 

Sodium pyrosulphate, or sodium anhydro-sulphate. NasS207... 

The isothermal solubility curve of mixtures of potassium sulphate and sulphuric acid expresses the composition of the soln. at 25° in equilibrium with the solid phase or phases, when the mol. ratio of K2SO4 and SO3 per 1000 grms. of soln. are plotted as co-ordinates. The ranges of stability in the ternary system K20—S03—H20, are diagrammed in Fig. 51, where the conditions have been studied in the vicinity of the SOs-apex, as far as the formation of KHS207, hut not as far as the well-known potassium pyrosulphate. The meaning of the diagram... 

Condensation can occur, however, with divalent complex ions besides the normal sulphates, pyrosulphates can be formed,... 

Pyrosulphuryl Chloride, S205C12.—Rose first prepared this substance in 1838 by the interaction of sulphur trioxide and sulphur monochloride.4 It is formed by the action of many chlorides on sulphur trioxide sulphur monochloride,4 thionyl chloride,5 silicon tetrachloride,6 phosphorus pentachloride,7 phosphorus oxychloride,8 sodium chloride 9 and carbon tetrachloride 10 all yield the desired product when treated with sulphur trioxide at a suitable temperature. With sodium chloride a mixture of pyrosulphufyl chloride and sodium pyrosulphate is obtained, whilst with the exception of carbon tetrachloride and phosphorus pentachloride, which are converted into oxychlorides, all the remaining chlorides are changed into oxides ... 

Potassium sulphate, when warmed with chlorosulphonic acid, yields potassium pyrosulphate,9 the reaction being analogous to that of sulphuric acid with the chloro-aeid silver nitrate is vigorously converted into silver chloride, with concurrent formation of nitrosulphonic acid.10... 

The pyrosulphates resemble their parent acid (see (3) (a)) in yielding sulphur trioxide when heated 4 a similar result is obtained on heating with sulphuric acid 5... 

Pyrosulphates.—The pyrosulphates of the alkali metals are obtained most easily by heating the corresponding acid sulphates to 300°- 350° C 4... 

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