Lower Oxo-Acids

The best-known oxo-acids of phosphorus are hypophosphorous acid, H3PO2, phosphorous acid, H3PO3, pyrophosphorous acid, H4P2O5, and hypophosphoric acid, H4P2O6. These were aU discovered in the nineteenth century, and are obtainable pure, as white crystalline solids which can be represented by the un-ionised formula. 

Phosphorous acid (phosphonic acid), H3PO3, mp = 73.8°C, is a very hygroscopic solid which is extremely soluble in water (425 g H3PO3 per 100 g H2O at 20°C). It decomposes above 180°C forming mainly phosphoric acid and phosphine. The acid can be obtained in low yield by the slow oxidation of white phosphorus in moist air, but the best method (used industrially) is by the hydrolysis of phosphorus trichloride (5.210). The hydrogen chloride is removed by heating under reduced pressure. 

Phosphorous acid may also be prepared by the reaction of phosphorus trichloride with anhydrous oxalic acid (5.211), or by the hydrolysis of P4O6 (4.68), but this last method is not used owing to difficulties in obtaining the lower oxide free from impurities. 

Phosphorous acid is dibasic and forms two series of salts corresponding to M2HPO3 and MH2PO3. As in the case of orthophosphoric acid, the first H atom is more readily ionised than the second  

NajHPOj-SHjO CuHP03-2Hj0 NaH2P03-2H20 

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Lower Oxo Acids of Phosphorus and Their Salts in Topics fn Phosphorus Chemistry, Vol. 1, M. Grayson, E. J. Griffith, Eds. (Interscience, New York. 1964) pp 113-187. 

Blaser and Worms (2) have proposed the use of the abbreviated notations that are shown in the 4th column of Table I. These notations are based on the linkages of phosphorus and oxygen that compose the framework of a given compound. A numeral attached to a phosphorus atom represents an oxidation number of the phosphorus atom. The reason that all lower oxo acids of phosphorus can be represented by means of abbreviated notations of this type is based on the fact that every phosphorus atom in the molecules of the lower oxo acids of phosphorus has the following structure V... 

The lower oxo acids of phosphorus that have been isolated as pure... 

Structural Types of Lower Oxo Acids of Phosphorus and Oxidation Numbers of... 

The chemistry of lower oxo acids of phosphorus has been surveyed by Van Wazer (5). Reviews on the recent development of the chemist-y... 

Prepaiatioii, structures, and properties of the lower oxo acids of phosphorus will be described in brief for the compounds that have been known for many years and in detail for the compounds that have been recently discovered. Reactions for preparation of the lower oxo acids of phosphonis or their salts are diagramatically illustrated in Figure 1. Reactions of aqueous solutions of the lower oxo acids of phosphorus and their salts with alkali hydroxide, mineral acids, and oxidizing agents are... 

Reactions Of Aqueous Solutions of Lower Oxo Acids of Phosph ... 

P-, P-, P-P-, P-, P-0-P-, (-P-0-)3-ring, (-P-0-)4-ring, and long chain metaphosphate anions, can be separated by two-dimensional paper chromatography. Blaser and Worms (19,41,44,47,50,56,65) employed Grunze and Thilo s solvents (72) for the identification of various lower 0X0 acids of phosphorus. Using Thilo and Heinz s basic solvent (73), Hamisch (4) demonstrated the separation of many lower oxo acids of phosphorus. 

Paper chromatographic, paper electrochromatographic, and thin layer chromatographic separation of lower oxo acids of phosphorus or their salts will be extended to the quantitative analysis of them. Further investigations in this field are desirable. 

It is possible to apply nuclear magnetic resonance spectroscopy to the quantitative differential determination of various lower oxo acids of phosphorus. The investigations along this line have not been well developed. 

Some of lower oxo acids of phosphorus and their salts in the crystalline states can be identified by x-ray diffractometry. Index to the X-ray... 

It is generally possible to determine a certain lower oxo acid of phosphorus in the absence of other phosphorus compounds or to determine total phosphorus contents in mixtures of various lower oxo acids of phos-... 

P-P-acid is the only lower oxo acid of phosphorus that can be deter-... 

The volumetric analysis of pure lower oxo acids of phosphorus and... 

Analysis of mixtures of lower oxo acids of phosphorus and their salts is a relatively difficult problem, especially when a number of the oxo acids or their salts are presen t in a given sample. The chemical approach to this problem is based on the fact that, under certain conditions, one acid will be readily oxidized or hydrolyzed and another will not. Preferential oxidation with halogens, particularly iodine, has been the basis of a number of procedures for differential analysis. 

The reactions of twelve lower oxo acids of phosphorus as well as... 

S. Ohashi, Lower oxo acids of phosphoms and their salts. Topics. Phos. Chem., 1, 149, 1965. 

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