Oxyacids of phosphorus

What products form when disubstituted sodium and ammonium-sodium orthophosphates are roasted What orthophosphates are used as fertilizers Compare the strength of the oxyacids of phosphorus, sulphur, and chlorine, and also of nitrogen and phosphorus. 

The numerous oxyacids of phosphorus may be regarded as derived from three prototypes, namely, hypophosphorous acid, H3P02, phosphorous acid, H3P03, and orthophosphoric acid, HsP04, in all of which phosphorus probably has the co-ordination number 4 (see p. 59). 

A third oxyacid of phosphorus is hypophosphorous acid (H3PO2) [Fig. 19.14(b)], which is a monoprotic acid. 

The same change, from classical general base to nucleophilic catalysis by selected nucleophilic bases, has been observed and studied recently for the hydrolysis of activated amides (an example is l-benzoyl-3-phenyl-l,2,4-triazole 2.2, Scheme 2.11) [21], and is observed also for esters of various oxyacids of phosphorus. The changeover to general base catalysis of the hydrolysis of aryl dialkyl phosphates... 

Phosphorous acids.—Five oxyacids of phosphorus are known ... 

Arsenic Acids. — The oxyacids of arsenic form a series, corresponding to that of the oxyacids of phosphorus, except that the hypoarsenious acid is unknown... 

Orthophosphoric (monophosphoric) add, H3PO4 (nsnaUy referred to as phosphoric acid), is the simplest oxyacid of phosphorus. It is stored and sold as an aqueous solution which is available in varions concentrations. The acid can be prepared by reacting phosphorus pentoxide with water (4.43). In the dry or thermal commercial process, the oxide is first prepared by bnming white phosphoms (Chapter 4.1). 

H.A.J. Champ, Reduced oxyacids of phosphorus and their salts, in Mellor s Comprehensive Treatise on Inorganic and Theoretical Chemistry, Vol. 8, Suppl. 3, Longmans, London, 1973. 

The total acidity, which includes other oxyacids of phosphorus (unlikely to be present in quantity, otherwise the acid would not pass the B.P.C, tests) can be titrated direct with alkali to methyl orange or bromophenol blue. 1 ml 0-5N = 0 03300 g. Hypophosphorous acid, after neutralisation may be determined by the methods described below for hypophosphites. 

H3PO3 is more clearly described with the structural formula HP0(0H)2. This species exists in equilibrium with a minor tautomer P(0H)3. IUPAC recommendations, 2005, are that the latter is called phosphorous acid, whereas the dihydroxy form is called phosphonic acid. Only the reduced phosphorus compounds are spelled with an "ous" ending. Other important oxyacids of phosphorus are phosphoric acid (H3PO4) and hypophosphorous acid (H3PO2). The reduced phosphorus acids are subject to similar tautomerism involving shifts of H between O and P. 

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