4- Oxoacid, oxidation

Oxides and oxoacids Oxides in the +3 and +5 oxidation state are increasingly polymeric with heavier elements. They form oxoacids, of which phosphoric acid is the most important. 

Graphite reacts rather differently with mixtures of oxidising agents and concentrated oxoacids. A graphite oxide is formed the graphite... 

Non-metals — These are often oxidised to the corresponding oxoacid, and nitrogen oxide is formed. For example, sulphur gives sulphuric acid with cold concentrated nitric acid ... 

With concentrated nitric acid, selenium and tellurium form only their +4 oxoacids, H2Se03 and H2Te03 respectively, indicating a tendency for the higher oxidation states to become less stable as the atomic number of the element is increased (cf. Group V, Chapter 9). 

The reversible intercalation of various oxoacids under oxidizing conditions leads to lamellar graphite salts some of which have been known for over a century and are now particularly well characterized structurally. For example, the formation of the blue, first-stage compound with cone H2SO4 can be expressed by the idealized equation... 

Numerous oxoacid salts of Sn and Sn have been reported and several basic salts are also known. Anhydrous Sn(N03)2 has not been prepared but the basic salt Sn3(0H)4(N03)2 can be made by reacting a paste of hydrous tin(II) oxide with aqueous HNO3 the compound may well contain the oligomeric cation [Sn3(OH)4] + illustrated on p. 384, Sn(N03)4 can be obtained in anhydrous reactions of... 

Most oxoacid derivatives of lead are Pb" compounds, though Pb(OAc)4 is well known and is extensively used as a selective oxidizing agent in organic chemistry.It can be obtained as... 

This section deals with the binary compounds that nitrogen forms with metals, and then describes the extensive chemistry of the hydrides, halides, pseudohalides, oxides and oxoacids of the element. The chemistry of P-N compounds is deferred until Chapter 12 (p. 531) and S-N... 

Reactions with sulfides, polysulfides, sulfur oxides and the oxoacids of sulfur are complex and the products depend markedly on reaction conditions (see also p. 745 for blue crystals in chamber acid). Some examples are ... 

The oxoacids of P are dearly very different structurally from those of N (p. 459) and this difference is accentuated when the standard reduction potentials (p. 434) and oxidation-stale diagrams (p. 437) for the two sets of compounds are compared. Some reduction potentials ( /V) in acid solution are in Table 12.8 (p. 513) and these are shown schematically below, together with the corresponding data for alkaline solutions. 

Figure 12.16 Oxidation state diagram for phosphorus. (Note that all the oxoacids have a phosphorus covalency of 5.)...

Table 12.9 Some lower oxoacids of phosphorus (Supcrscripl numerals in the abbreviated notation indicate oxidation stales)...

The amphoteric nature of AS2O3 and the trends in properties of several of the oxides and oxoacids... 

The formal interrelationship between the various oxoacids of sulfur can also be illustrated in a. scheme which places less emphasis on oxidation-reduction reactions but which is useful in suggesting possible alternative synthetic routes... 

The ricji oxoacid chemistry of sulfur (pp. 705-21) is not paralleled by the heavier elements of the group. The redox relationships have already been summarized (p. 755). Apart from the dark-brown hydrated monoxide Po(OH)2 , which precipitates when alkali is added to a freshly prepared solution of Po(ll), only compounds in the +4 and +6 oxidation states are known. 

In the -1-6 oxidation state the oxoacids of 8e and Te show little resemblance to each other. H28e04 resembles H28O4 (p. 710) whereas orthotelluric acid Te(OH)g and polymetatelluric acid (H2Te04) are quite different. 

More detailed consideration of these various equilibria and other redox reactions of the halogen oxoacids will be found under the separate headings below. As expected, the rates of redox reactions of the halogen oxyanions will depend, sometimes crucially, on the precise conditions used. However, as a very broad generalization, they tend to become progressively faster as the oxidation state of the halogen decreases, i.e. ... 

The group oxidation state of +5 is too high to allow the formation of simple ionic salts even for Nb and Ta, and in lower oxidation states the higher sublimation energies of these heavier metals, coupled with their ease of oxidation, again militates against the formation of simple salts of the oxoacids. As a consequence the only simple oxoanion salts are the sulfates of vanadium in the oxidation states +3 and +2. These can be crystallized from aqueous solutions as hydrates and are both strongly... 

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