Oxidation State of Phosphorus

In all cases the oxidation state of phosphorus is five, and the chemical shift range observed is only about 12 ppm. Note that the two phosphorus atoms attached to the methine carbon are non-equivalent because they are chemically different (phosphonate and phosphine oxide). We can expect the coupling between aP and bP to be large, as they are separated by two bonds, while that of aP to bP or CP will be small (coupling over five bonds). 

It is probable that the prevalent oxidation states of phosphorus on the young Earth were lower than they are today, so calcium salts with a much better solubility than that of apatite could have been formed. As Glindemann et al. (1999) were able to show in model experiments, up to 11 % of the starting material could be converted to phosphite in CH4/N2 atmospheres (10% CH4) using Na2HP04, hydroxyapatite or fluoroapatite sources. Similar processes cannot be excluded for the primeval Earth, for example, under the influence of electrical discharges. 

Braun U, Balabanovich AI, Schartel B, Knoll U, Artner J, Ciesielski M, Doring M, Perez R, Sandler JKW, Altstadt V, Hoffmann T, Pospiech D. Influence of the oxidation state of phosphorus on the decomposition and fire behaviour of flame-retarded epoxy resin composites. Polymer 2006 47 8495-8508. 

The XPS and P-KLL Auger electron spectra of the phosphorus(III/ V) oxide sulfides P406S and P406S2 80) do not show any significant splitting as would be expected due to the different oxidation states of phosphorus. This finding has not been understood so far further experimental and theoretical work is required. 

Ans. The more electronegative element will take the negative oxidation state, (a) The maximum oxidation state of sulfur is +6 the only oxidation number of fluorine in its compounds is — 1. Therefore, it takes six fluorine atoms to balance one sulfur atom, and the formula is SFg. (b) The maximum oxidation state of phosphorus is +5 the most common negative oxidation number of oxygen is —2. Therefore, it takes five oxygen atoms to balance two phosphorus atoms, and the formula is P2O5. 

Predicting Consider the fact that all of the following are stable compounds. What can you infer about the oxidation state of phosphorus in its compounds ... 

As a final example, consider phosphorous acid H3P03 (5). The oxidation state of phosphorus is +3,... 

We now have to prove our assumption by correlating phosphorus chanical shifts with the oxidation state of phosphorus in a range of molecules. If the oxidation state correlates with the chemical shift, then we will find well-defined blocks of molecules that experience a downfield shift with increasing oxidation state. If our assumption is true, however, then we will find that for each oxidation state, the constituting molecules will cover a broad range of chemical shift values, and that these blocks have large overlap areas. 

Use Figure 7.4b to say something about the relative stabilities of the different oxidation states of phosphorus in aqueous media at pH 0. 

Hergenrother et al. have calculated the flaming combustion efficiency of epoxy resins prepared from various epo>y- or amine-functional organo-phosphorus compounds by dividing the EHC measured in fire calorimetiy tests (Ohio State University apparatus and cone) by the effective heat of complete combustion measured in a PCFC. The combustion efficiency ranged roughly from 0.6 to 0.8 versus 0.7 for the phosphorus-free epo)y resin) whatever the oxidation state of phosphorus and other parameters. The authors concluded that there is no discernible effect [...] on the combustion efficiency in the flame . 

The arithmetic is correct, significant figures have been used correctly, and units cancel as desired. The formula is reasonable because -1-5 is a common oxidation state of phosphorus. 

Note that the oxidation state of phosphorus does not change in either one of these hydrolysis reactions.) In soHd form, PCI5 is actually made up of alternating PCI4 and PCl ions. 

Phosphorus is one of the most significant impurity elements in the Hall-Heroult process for producing aluminium. High levels of phosphorus affect some important properties of aluminium and aluminium alloys. Also the current efficiency for aluminium is lowered due to cyclic red/ox reactions at the electrodes involving different oxidation states of phosphorus. Several studies in industrial cells have shown that a content of 100 ppm phosphorus in the bath reduces the current efficiency by about 1% [1]. In a more controlled laboratory study [2] it was found that the current efficiency was reduced by 0.72% per 100 ppm P in the electrolyte. Thisted and coworkers carried out similar experiments and obtained similar results [3,4]. Figure 1.7.1 shows the reported results of the effects of phosphorus on the current efficiency for aluminium deposition. 

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