Pentoxide, phosphorus

White crystalline deliquescent powder mp, 340°C. Sublimation temperature, 36 0 ,C.1 

Formic Acid. Attempted dehydration of 95% acid caused rapid evolution of CO.2 Hydrogen Fluoride. Vigorous interaction below 20°C.3 

Inorganic Bases. Mixtures with Na20 or CaO react violently if warmed or 

Metals. Reaction with warm Na or K is incandescent reaction with Ca is explosive when heated.6 

Dust irritates the respiratory system and burns the eyes and skin. Swallowing would cause internal irritation and damage. Prevent contact with eyes and skin.8 

The structural chemistry of this oxide in the solid and liquid states is complex. In addition to a high-pressure form and a glass there are three polymorphs stable at atmospheric pressure. As noted in Chapter 3 these three crystalline fomis represent 

The structures of the molecules (a) P4, (b) P4O6, and (c) P4O10 in the vapour state (diagrammatic). Shaded circles represent P atoms. 

The P4O10 molecule has been studied in the vapour by e.d. with the results summarized in Table 19.5. The unshared (outer) 0 atoms are distinguished as O the (multiple) bond P-O is the shortest recorded phosphorus-oxygen bond. 

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Dehumidification may be effected by cooling. Where small quantities of dry air are required dehumidification can be carried out using chemical absorbents, e.g. calcium chloride, phosphorus pentoxide, sulphuric acid, etc. 

This oxide was originally given the formula P2O5 and called phosphorus pentoxide but the vapour density and structure indicate the formula P40,q. It is prepared by burning phosphorus in a plentiful supply of air or oxygen ... 

Unlike phosphorus pentoxide, this oxide cannot be made directly. Arsenic(V) acid, H3ASO4 (strictly, tetraoxoarsenic acid), is first prepared by oxidising arsenic(III) oxide with concentrated nitric acid or some other strong oxidising agent ... 

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

The crude acetonitrile contains as impurity chiefly acetic acid, arising from the action of phosphoric acid on the acetamide. Therefore add to the nitrile about half its volume of water, and then add powdered dry potassium carbonate until the well-shaken mixture is saturated. The potassium carbonate neutralises any acetic acid present, and at the same time salts out the otherwise water-soluble nitrile as a separate upper layer. Allow to stand for 20 minutes with further occasional shaking. Now decant the mixed liquids into a separating-funnel, run off the lower carbonate layer as completely as possible, and then pour off the acetonitrile into a 25 ml, distilling-flask into which about 3-4 g. of phosphorus pentoxide have been placed immediately before. Fit a thermometer and water-condenser to the flask and distil the acetonitrile slowly, collecting the fraction of b.p. 79-82°. Yield 9 5 g. (12 ml.). 

Phosphorus pentoxide. This is an extremely efficient reagent and is rapid in its reaction. Phosphoric oxide is difficult to handle, channels badly, is expensive, and tends to form a syrupy coating on its surface after a little use. A preliminary drying with anhydrous magnesium... 

Alkyl halides Aryl halides Anhydrous calcium chloride anhydrous sodium, magnesium or calcium sulphate phosphorus pentoxide. 

Saturated and aromatic hydrocarbons Ethers Anhydrous calcium chloride anhydrous calcium sulphate metallic sodium phosphorus pentoxide. 

By the dehydration of primary amides with phosphorus pentoxide or with thionyl chloride, for example ... 

Place 45 g. of benzamide (Section IV, 188) and 80 g. of phosphorus pentoxide in a 250 ml. Claisen flask (for exact experimeutal details on the handling and weighing out of phosphoric oxide, see under Acetamide, Section 111,111). Mix well. Arrange for distillation (Fig.//, 29, 1 or Fig. II, 20, 1) under reduced pressure use a water pump with an air leak in the system so that a pressure of about 100 mm. is attained. Heat the flask with a free flame until no more liquid distils the nitrile will pass over at 126-130°/100 mm. Wash the distillate with a little sodium carbonate solution, then with water, and dry over anhydrous calcium chloride or magnesium sulphate. Distil under normal pressure (Fig. II, 13, 2 or II, 13, 6) from a 50 ml. flask the benzonitrile passes over as a colourless liquid at 188-189° (compare Section IV,66). The yield is 28 g. 

A solution of 0.10 mol of freshly distilled diethylaminopropyne in 80 ml of dry (distilled from phosphorus pentoxide) acetonitrile was cooled to 5°C and dry carbon dioxide was introduced into the vigorously agitated solution at a rate of about 0.3 1/min. The temperature rose above 20°C within a few minutes, but was kept at about 30°C by occasionally immersing the flask in a bath of ice-water. The introduction of CO2 was continued until the temperature had dropped to 25°C and the typical odour of the yneamine had disappeared completely. The yellow solution was concentrated in a water-pump vacuum. The residue, a sirupy liquid, had the theoretically required weight and consisted of reasonably pure (about 955 ) allenyl-diamide. If desired the product car be distilled (short-path distillation) in a high vacuum. It solidified upon standing at -25 C. 

Thiazole carboxamides are readily dehydrated to nitriles in good yields by heating with phosphorus oxychloride (91), phosphorus pentoxide (87, 71), or phosphoryl chloride (16) (Scheme 19). 

Phosphorus pentoxide to titration from yellow ppt. P2O5 0.0019715... 

Ammonia, anhydrous Mercury, halogens, hypochlorites, chlorites, chlorine(I) oxide, hydrofluoric acid (anhydrous), hydrogen peroxide, chromium(VI) oxide, nitrogen dioxide, chromyl(VI) chloride, sulflnyl chloride, magnesium perchlorate, peroxodisul-fates, phosphorus pentoxide, acetaldehyde, ethylene oxide, acrolein, gold(III) chloride... 

Phosphorus pentoxide Formic acid, HF, inorganic bases, metals, oxidants, water... 

Propyn-l-ol Alkali metals, mercury(II) sulfate, oxidizing materials, phosphorus pentoxide, sulfuric acid... 

Phosphorus Pentoxide. Phosphoms compounds form PF or POF compounds in the furnace. Some may be hydroly2ed to higher boiling forms in downstream process operation. Some of the phosphoms compounds do appear in the final product. This is objectionable to some users. 

Peroxomonophosphoric acid can be prepared by the hydrolysis of peroxodiphosphates ia aqueous acid and by the reaction of hydrogen peroxide with phosphorus pentoxide (45). It is not produced or used commercially and the salts that have been prepared are unstable and impure. 

Table 5. Air-Blowing of Fluxes With and Without Ferric Chloride and Phosphorus Pentoxide Catalysts...

Phosphorus Pentoxide. This compound, P2O55 (Class 1, nonregenerative) is made by burning phosphoms ia dry air. It removes water first by adsorptioa, followed by the formation of several forms of phosphoric acid (2). Phosphoms peatoxide [1314-56-3] has a high vapor pressure and should only be used below 100°C. Its main drawback is that as moisture is taken up, the surface of the granules becomes wetted and further moisture removal is impeded. For this reason, phosphoms pentoxide is sometimes mixed with an iaert material (see Phosphoric acids and phosphates). 

When saccharin is treated with diethyl phosphorothiolothionate, the 3-ethylmercapto compound is obtained, rather than the expected organophosphorus compound (77 ACS(B)460). Treatment of saccharin with phosphorus pentoxide and amines gives 3-(substituted-amino)-1,2-benzisothiazole 1,1-dioxides, via an intermediate phosphate (81ZN(B)1640). Reduction of saccharin with zinc and hydrochloric acid gives 2,3-dihydro-l,2-benzisothiazole 1,1-dioxide, the method being used to estimate saccharin in foodstuffs (75MI41701). 

The separatory funnel is now replaced by a wide glass tube (about 12 mm. internal diameter) which passes well into the flask but does not dip below the surface of the liquid (Note 2). This tube connects directly with a 500-cc. round-bottom flask containing 50 g. of paraformaldehyde which has been previously dried for two days in a vacuum desiccator over phosphorus pentoxide. The stirrer is started (Note 3) and the flask containing the paraformaldehyde is heated in an oil bath to 180-200°,... 

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. ... 

The 1,2-dichloroethane available from Aldrich Chemical Company was distilled from phosphorus pentoxide before use. Although less effective, dichloromethane may also be used in the carbometallation step. 

The crude material from one run melted at 125-143°, but the melting point changed to 140-150° upon drying over phosphorus pentoxide at 100° under a pressure of 10 mm. Another crude sample melted at 145-147°. 

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