Oxoacids of phosphorus

The absorption at 2408cm in the IK spectrum of aqueous H3PO2 shifts when the sample is fidly deuterated. Explain why this shift occurs, and calculate the wavenumher at which the new hand should he ohserved. lAns. 1735 cm  

When heated, H3PO2 disproportionates according to equation 15.127, the products being determined by reaction temperature. 

Intramolecular transfer of a proton to the terminal O atom in phosphinic acid produces a tautomer in which the P atom is 3-coordinate  

Phosphonic acid (often called phosphorous acid) may be crystallized from the solution obtained by adding ice-cold water to P4O6 (equation 15.122) or PCI3 (equation 15.75). Pure H3PO3 forms colourless, deliquescent crystals (mp 343 K) and in the sohd state, molecules of the acid (Table 15.7) are hnked by hydrogen bonds to form a 3-dimensional network. In aqueous solution, it is dibasic (equations 15.128 and 15.129). 

Salts containing the [HPO3] ion are called phosphonates. Although the name phosphite remains in common use, it is a possible source of confusion since esters of type P(OR)3 are also called phosphites, e.g. P(OEt)3 is triethylphosphite. 

Arsenic(III) oxide dissolves in aqueous alkali to give salts containing the [As02] ion, and in aqueous HCl with the formation of ASCI3. The properties of Sb203 in water and aqueous alkali or HCl resemble those of AS2O3. 

Bismuth(III) oxide occurs naturally as bismite, and is formed when Bi combines with O2 on heating. In contrast to earlier members of group 15, molecular species are not observed for Bi203, and the structure is more like that of a typical metal oxide. 

Arsenic(V) oxide is most readily made by reaction 14.120 than by direct oxidation of the elements. The route makes use of the fact that AS2O5 is the acid anhydride of arsenic acid, H3ASO4. In the solid state, AS2O5 has a lattice structure consisting of As—O—As linked octahedral AsO and tetrahedral As04-units. 

Antimony(V) oxide may be made by reacting Sb203 with O2 at high temperatures and pressures. It crystallizes with a lattice structure in which the Sb atoms are octahedrally sited with respect to six O atoms. Bismuth(V) oxide is poorly characterized, and its formation requires the action of strong oxidants (e.g. alkaline hypochlorite) on Bi203. 

These oxides are mixed P(III)P(V) species, each centre bearing a terminal 0x0 group being oxidized to P(V). For example, P4O8 is made by heating P4O5 in a sealed tube at 710 K, the other product being red phosphorus. 

O atoms are involved in interconnecting the PO4 units via P-O—P bridges. Phosphoms(V) oxide has a great affinity for water (eq. 15.127), and is the anhydride of the wide range of oxoacids described in Section 15.11. It is used as a drying agent (see Box 12.3). 

Three other oxides of phosphorus, P4O7 (15.60), P4O8 (15.61) and P4O9 (15.62), have structures that are related to those of P4O6 and P4O10. 

The normal combustion products of As and Sb are As(III) and Sb(III) oxides (eq. 15.13). The vapour and high-temperature solid polymorph of each oxide contains E4O6 

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

Oxoacids of phosphorus and their salts Table 12.10 Factors affecting the rate of polyphosphate degradation... 

Many compounds containing the P-N link can be considered formally as derivatives of the oxoacids of phosphorus and their salts (pp. 510 -31) in which there has been isoclccironic replacement of ... 

Oxides and Oxoacids of Phosphorus When phosphorus burns in air or oxygen, it yields tetraphosphorus hexoxide (P4Og, mp 24°C) or tetraphosphorus decoxide (P4Oio, mp 420°C), depending on the amount of oxygen present ... 

A diverse range of oxoacids of phosphorus is known. The presence of hydrogen in such systems is either in the form... 

It is also well known (2) that not all oxoacids of phosphorus react with molybdenum ion to form a positive blue complex at the same rate. Time studies were done on plasma PSG wafers. Figure 1 shows distinct differences between the phosphate ion and doped oxide film from a wafer when analyzed with and without oxidation. 

Many possible compounds of phosphorus exist. The simplest are listed in Table I. Even more complicated oxoacids of phosphorus were studied and reported in the paper by Ohashi and Yoza (3). Their study of oxoacids of phosphorus with molybdenum ion was done in neutral and acid solutions in the presence and absence of a reducing agent. Their results showed that acids containing a -P-P-P straight or cyclic chain gave color development similar to those we found in... 

Figure 2. Time study on oxoacids of phosphorus molybdate blue reaction.

Table 14.7 lists selected oxoacids of phosphorus. This is an important group of compounds, but the acids are difficult to classify in a straightforward manner. It should be remembered that the basicity of each acid corresponds to the number of OH-groups, and not simply to the total number of hydrogen atoms, e.g. H3PO3 and H3PO2 are dibasic and monobasic respectively (Table 14.7). Diagnostic absorptions in the IR spectra of H3PO3 and H3PO2 confirm the presence of P—H bonds the P-attached hydrogens do not ionize in aqueous solution.

Table 14.7 Selected oxoacids of phosphorus older names that are still in common use are given in parentheses.

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