P4O6 PHOSPHORUS TRIOXIDE

Phosphorus(lII) oxide, P4O6, phosphorus trioxide, m.p. 24°C, b.p. 174 C. A waxy material (burn P in deficiency of O2)- It burns in excess O2 to P2OJ, reacts with, e.g. CI2 to POCI3 and dissolves in water to give phosphorus(TII) oxyacids. The structure is similar to that of P40,o but without the terminal oxygens. 

Fig. 3. n.m.r. spectra of a series of compositions made by bubbling diborane through a chloroform solution of phosphorus trioxide. The overall stoicheiometry of each composition is given by the mole ratio, R = BH3/P4O6, and the sets of resonances corresponding to individual molecular species are differentiated by the numbers 1, 2 or 3. (From Van Wazer. )... 

Phosphorus trioxide, P4O6, can be made by burning phosphorus in a restricted supply of oxygen. It is a colourless crystalline material with mp = 23.8°C and bp = 175.4°C, and it can be crystallised from carbon disulphide solution. The solid is built from tetrahedral units (4.41e) which are similar to those established in the vapour by electron diffraction and vapour density measurements. 

Phosphorus trioxide forms various addition complexes using its lone pair electrons to complete a tetrahedral configuration (Figure 4.10). With diborane it forms P4O6 nBHj, and with nickel carbonyl it forms P40g nNi(C0)4, where n = 1-4 (Chapter 10). Phosphorus is obtained on heating phosphorus trioxide with arsenic or antimony in a sealed tube (4.75). Recent work [8] has shown that the trioxide also reacts with ozone at low temperatures to form an ozonide of composition P40,g (4.66c). Another substitution in the cage molecule is (4.76) [9]. 

Oxides of Phosphorus The simplest formulas we can write for the oxides that have phosphorus in the oxidation states +3 and +5 are P2O3 and P2O5, respectively. The corresponding names are "phosphorus trioxide" and "phosphorus pentoxide." P2O3 and P2O5 are only empirical formulas, however. The true molecular formulas of the oxides are double those— that is, P4O6 and P4O10. 

Phosphorous trioxide, P4O6, is present in the atmosphere of Venus [34]. Spectroscopic molecules such as PH, PO, PN, PC and more recently HC P, have all been detected in interstellar space. Recent studies [36] have supported earlier views [37] that phosphorus may have originally been present on Earth in a reduced oxidation state, for example, as derivatives of phosphonic (phosphorous) acid H3PO3 rather than of phosphoric acid H3PO4. Recent studies have confirmed that condensed phosphates (which are needed for the production of evolutionary DNA) can be produced by oxidation of phosphonates or phosphinates [38]. The identification of sulphate-reducing bacteria (Chapter 11.7), also suggests a means by which P could have become fully oxidised during the course of planetary evolution. Natural phosphine gas, PH3, may also result from bioreduction processes (Chapter 4.4). 

---