Pyro-acids

Product Quality. Under ideal plant operating conditions, the quahty of products derived from continuous SO film sulfonator units is unlikely to be significantly different (1). Typical LAB sulfonic acid composition is ca 96.6% active sulfonic acid, 1.2% free oil, 1.2% H2SO4, and 1.0% water, the last added for stabilization purposes to break sulfonic acid anhydrides and pyro-acids (279). Klett color for a 5% active solution is typically 15—25. 

Disfture,/. diacid (often, pyro acid). Disazo-farbstoff, m. disaso dye. -vertnndung, /, disazo compound,... 

Pyro-phosphorsaure, /. pyrophosphoric acid, -saure, /. pyro acid, -schleimsaure, /. pjto-mucic acid, furoic acid, -schwefelsaure, /. pyrosulfuric acid, disulfuric acid (H2S2O7). 

The formulas of meta and pyro acids are related to the ortho acids that you learned on p 107 (the exception is HN03, which is meta nitric acid), as follows ... 

The results for the pyro-acid are so much like those for hypophosphoric acid, that E. Cornec argued a like complexity for the molecules of the two acids. G. A. Abbott and W. C. Bray calculated that with soln. containing c millimols of pyrophosphoric acid per litre, the degree of ionization, and the ionization constants, are ... 

Some physical properties of metaphosphoric acid.—Metaphosphoric acid is a transparent, vitreous solid sometimes called glacial phosphoric add. E. Brescius2 said that the glacial acid is soft and flexible, and the presence of sodium phosphate makes it hard. The commercial acid is sold in sticks, and, according to A. Betten-dorff, it often contains some sodium salts and some ortho- and pyro-acids as impurities. The dry acid deliquesces rapidly in air, and it readily dissolves in water with the development of much heat. The acid solidifies to a vitreous mass without crystallization from solutions with less than 63 per cent, of water. 

At the same time Meyer also isolated pyro acid of (MeSn)407H2 composition. It appeared to be a cross-linked polymer, corresponding to the formula HO(MeSnOi.5)4H. 

Orthocarbonic acid has not been made, but esters of this hypothetical acid have been long known.) An acid that may be formed (at least formally) by removal of one molecule of water from two molecules of the ortho acid is termed the pyro acid, whereas the acid formed by removal of one molecule of water from a single molecule of the orthoacid is called the meta acid ... 

The molar refraction was 23-6.1 The equivalent refracting power of the H2P04 ion has been calculated as 21-6.2 Refractivities may conveniently be used in determining the concentration of aqueous solutions and also in testing for freedom from the meta- and pyro-acids.3... 

Ordinary oxidising agents have no effect, but with the meta- or pyro-acid hydrogen peroxide gave perphosphoric acid (q.v. p. 184). 

A mixture of the ortho- and meta-acids may be condensed together to form the pyro-acid by heating on the water-bath, thus —... 

Aqueous vapour pressures in equilibrium with the meta-acid are much lower than those over the pyro-acid. The pressure over the pyro-acid became appreciable at 100° C. and reached 100 mm. somewhat above 160° C., while that over the meta-acid became appreciable at 190° C. and reached 100 mm. a little over 240° C.3... 

It cannot be assumed that, because pyrophosphoric acid is produced as an intermediate product in the dehydration of H3P04 that it will also be produced during the hydration of HP03. The amounts observed may be present in the original HP03 or be produced by the heat developed when this is placed in water. The pyro-acid has been detected in the last fractional precipitates of silver phosphates, etc. (see Estimation ).2 Since there is some evidence that metaphos-phoric add is hydrated more rapidly than pyrophosphoric acid6 the latter may accumulate up to a certain maximum concentration. 

At a temperature of 78° C. the velocity constant whether referred to a unimolecular or a bimolecular reaction diminished with time after an hour rather less than three-quarters of the original metaphosphate remains.6 The product is mainly orthophosphate, as was proved by titration with methyl orange and phenolphthalein, although small quantities of pyrophosphate were formed by a side reaction. The pyro-acid was determined by titration to bromophenol blue in the presence of zinc sulphate, which leads to a complete precipitation of pyrophosphate, the ortho-acid being unaffected, thus... 

IV.23 BORATES,B03 ,B407r,B02 The borates are derived from the three boric acids orthoboric acid, H3B03, pyroboric acid, H2B407, and metaboric acid, HB02. Orthoboric acid is a white, crystalline solid, sparingly soluble in cold but more soluble in hot water very few salts of this acid are definitely known. On heating orthoboric acid at 100°, it is converted into metaboric acid at 140° pyroboric acid is produced. Most of the salts are derived from the meta-and pyro-acids. Owing to the weakness of boric acid, the soluble salts are hydrolysed in solution and therefore react alkaline. 

Whereas pyro acids, for example, pyrosulfurie, H2S207, discussed in Chapter 5 (page 181), usually have oxygen bridges, the pyrosulfite ion has an S—S bond and hence an unsymmetrical structure, 02S—S03(Cs).60 Some important reactions of sulfites are shown in Fig. 15-11. 

When phosphorus pentoxide, or as it is commonly called phosphoric anhydride, is put into cold water, the meta acid is formed. Upon boiling this slowly it reacts with more water and produces the ortho acid. The pyro acid which might be expected as an intermediate product is not formed. This acid, or more usually one of its salts, can be prepared, however, by... 

The purified 53% D3PO4 solution is concentrated to 83% at 45°C in the apparatus shown in Fig. 195 (p. 543). No pyro acid should be produced at this tenqierature. The course of the concentration is observed by weighing the cooling trap. Further concentration by evaporation is inipossible because partial conversion to the pyro acid occurs. 

The acid is converted into the corresponding pyro acid when it is distilled under vacuum (Scheme 4.3). 

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