Phosphorus Pentoxide Phosphoric Anhydride

Phosphorus pentoxide, P4O10, the most important oxide, is obtained when phosphorus is burnt in an excess of dry air or oxygen (4.42). It was first prepared in this manner by Boyle in 1680 [7]. 

On the commercial scale, phosphorus vapour is burnt in a specially designed burner, in a current of air which has been dried by refrigeration or other methods. The phosphoric oxide vapour so formed passes to a cooling chamber where it condenses to the familiar white powder. It may be purified from possible traces of lower oxides by sublimation in an oxygen atmosphere. 

The common form of phosphorus pentoxide is an exceedingly hygroscopic white powder, p = 2.30 g/cc, which sublimes at 359 C, but if heated rapidly melts at about 423°C. It combines avidly with water, forming orthophosphoric acid in the strongly exothermic reaction (4.43). It can cause burns (Appendices 2 and 3). 

This oxide finds much use as a desiccant, but it has the great disadvantage that it skins with a mixture of metaphosphoric acids (Table 4.11), which are formed as intermediate products in reaction (4.43). This effect may be alleviated to some extent by spreading the oxide over a large surface, for example, glass wool or mixing it with activated carbon (Table 4.10). 

There are many various industrial uses for the pentoxide (Chapters 12.1 and 12.18). When heated with metal oxides, various mixed oxides can be obtained. These form useful glasses and other 

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Phosphorus Pentoxide (Phosphoric anhydride, Phosphoric oxide, Diphosphorus pentoxide). 

Phosphorus Pentoxide (Phosphoric anhydride. Phosphoric oxide. Diphosphorus pentoxide). P20s,mw 141.96 a soft, white powder absorbs moisture from the air with avidity, forming meta-, para-, or orthophosphoric acid, depending upon amt of w absorbed and upon conditions of absorption mp 580-585°, bp subl at 300°, d... 

Phosphorus pentoxid—Phosphoric anhydride Phosphoric oxid —PaOj—142—is formed when P is burned in an excess of dry O. It is a white, flooculent solid, which has almost as great a tendency to combine with HjO as has P2O3. It absorbs moisture rapidly, deliquescing to a highly acid liquid, containing, not phosphoric, but metaphosphoric acid. It is used as a drying agent. 

Alternate Names phosphorus pentoxide phosphoric anhydride. 

The hazards associated with occupational exposure to phosphoric acid depend on its acidic nature. Concentrated phosphoric acid is corrosive to exposed tissue, and lower concentrations are irritating to the skin, eyes, and mucous membranes. Phosphoric acid has a low vapor pressure at room temperature and is unlikely to present an inhalation hazard unless introduced into the atmosphere as a spray or mist. Unacclimated workers could not endure exposure to fumes of phosphorus pentoxide (the anhydride of phosphoric acid) at a concentration of lOOmg/m exposure to concentrations between 3.6 and 11.3mg/m produced cough, whereas concentrations of... 

Phosphorylation O-Benzyl phosphorus 0,0-diphenylphosphoric anhydride. 2-Cyanomethyl phosphate. Dibromomalonamide. Di-p-nilrobenzylphosphoryl chloridate. Dioxane diphosphate. Diphenylphosphorochloridate. Ethoxyacetylene. Metaphosphoric acid. o-Phenyl-ene phosphorochloridate. Phosphoric acid, anhydrous. Phosphorodimorpholidic chloride. Phosphorus pentoxide-Phosphoric acid. Phosphoryl chloride. Polyphosphoric acid. Pyro-phosphoryl tetrachloride. Silver dibenzyl phosphate. Silver diphenyl phosphate. Tetra-p-nitrophenyl pyrophosphate. 

Synonyms Diphosphorus pentoxide Phosphoric anhydride Phosphorus (V) oxide Phosphorus pentaoxide... 

Phosphoric acid-nitric acid - 647, 738 Phosphoric acid pickling solution - 696 Phosphoric acid scrap liquor - 44, 45 Phosphoric acid slurry - 697 Phosphoric acid-sulfuric acid - 697, 725 Phosphoric acid, wet process - 697, 698 Phosphoric anhydride (see Phosphorus pentoxide) Phosphorous acid - 42, 43, 237, 245, 386, 390, 554,661,795... 

Dehydration of the corresponding acid amides. This process usually requires phosphorus pentoxide (correctly termed phosphoric anhydride) as a dehydrating agent. 

Phenyl isothiocyanate has been prepared from thiocarbanilide by the action of phosphorus pentoxide, hydrochloric acid, iodine, phosphoric acid, acetic anhydride, and nitrous acid. It has also been prepared from ammonium phenyl dithiocarbamate by the action of ethyl chlorocarbonate, copper sulfate lead carbonate, lead nitrate, ferrous sulfate,and zinc sulfate. ... 

Phosphorsaure, /. phosphoric acid, -anhydrid, n. phosphoric anhydride (phosphorus pentoxide). -losimg, /. phosphoric acid solution, -salz, n. phosphate. 

A. Trifluoromethanesulfonic Anhydride. To a dry, 100-ml., round-bottomed flask are added 36.3 g. (0.242 mole) of trifluoromethane-sulfonic acid (Note 1) and 27.3 g. (0.192 mole) of phosphorus pentoxide (Note 2). The flask is stoppered and allowed to stand at room temperature for at least 3 hours. During this period the reaction changes from a slurry to a solid mass. The flask is fitted with a short-path distilling head and then heated first with a stream of hot air from a heat gun and then with the flame from a small burner. The flask is heated until no more trifluoromethanesulfonic anhydride distills, b.p. 82-115°. The yield of the anhydride, a colorless liquid, is 28.4-31.2 g. (83-91%). Although this product is sufficiently pure for use in the next step of this preparation, the remaining acid may be removed from the anhydride by the following procedure. A slurry of 3.2 g. of phosphorous pentoxide in 31.2 g. of the crude anhydride is stirred at room temperature in a stoppered flask for 18 hours. After the reaction" flask has been fitted with a short-path distilling head, it is heated with an oil bath to distill iD.7 g. of forerun, b.p. 74—81°, followed by 27.9 g. of the pure trifluoromethanesulfonic acid anhydride, b.p. 81-84° (Note 3). 

Nakagome and co-workers effected the successful cyclization of N-ethyl-N-arylaminomethylenemalonates (749) in poly phosphoric acid, prepared from orthophosphoric acid and phosphorus pentoxide in polyphosphate ester (PPE), prepared from phosphorus pentoxide and anhydrous diethyl ether in chloroform in phosphoryl chloride on the action of boron trifluoride etherate on the action of acetic anhydride and concentrated sulfuric acid or on the action of phosphorus pentoxide in benzene [71GEP2033971, 71JHC357 76JAP(K) 18440]. Depending on the work-up process, l-ethyl-4-oxoquinoline-3-carboxylates (750, R1 = Et), l-ethyl-4-oxoquinoline-3-carboxylic acids (750, R2 = H) and 3-ethoxycarbonyl-4-chloroquinolinium iodides (751) were obtained. Only the cyclization of... 

Several catalysts have been recommended for the N-acetylation of carbazole with acetic anhydride boron trifluoride, phosphorus pentoxide, concentrated sulfuric acid, zinc chloride, and phosphoric acid all gave 9-acetylcarbazole in moderate to good yield. 9-Acetylcarbazole can also be prepared using the Vilsmeier complex of N,N-dimethylacetamide and phosgene. ... 

Phenylacetylene, 72 /ra X-TPHENYL-l,3-BUTAniENE, 75 a-PHENYL-a-CARBETHOXYGLUTARO-NITRILE, 80, 82 0-Phenylenediamine, 56, 86 a-Phenylglutaric acid, 82 a-PHENYLGLUTARIC ANHYDRIDE, 81 Phenylhydrazine, 90 Phenylmagnesium bromide, 97 Phenylsuccinic acid, 83 Phenylsuccinic anhydride, 85 Phosphoric acid, ortho-, 33, 34 Phosphoric anhydride, 33 Phosphorus oxychloride, Tl Phosphorus pentoxide, 22, 46 Potassium, 19, 20 directions for safe handling of, 20 Potassium lerl.-butoxide, solution of, 19... 

Phosphorous oxide was formerly stated to deliquesce rapidly in air, and to dissolve in water with a hissing noise indeed, J. J. Berzelius said that the attraction of the anhydride for the moisture of the air develops so much heat that the oxide takes fire. The ignition of phosphorous oxide when shaken in air was shown by R. Cowper and V. B. Lewes to be due to the presence of very finely-divided yellow phosphorus —vide supra—and the hissing noise developed by contact with water is probably due to the presence of phosphorus pentoxide, because T. E. Thorpe and A. E. H. Tutton... 

Figure 7.2 illustrates the phosphorus pentoxide-mediated dehydration of a primary amide to a nitrile, using the transformation of nicotine amide (A) into nicotine nitrile (B) as an example. The reaction of phosphorus pentoxide at the carboxyl oxygen furnishes the partially ring-opened iminium ion E (simplified as F) via the polycyclic iminium ion C. E is deprotonated to give the mixed anhydride G from imidic acid and phosphoric acid. Imidic acids are characterized by the functional group R-C(=NH)-OH. This anhydride is transformed into the nitrile B by an El elimination via the intermediate nitrilium salt D. Nitrilium salts are iV-pro-tonated or V-alkylated nitriles. 

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