PC15 PHOSPHORUS PENTACHLORIDE

PC15 PHOSPHORUS PENTACHLORIDE 30.0396 -6.2579E+03 -7.4964E-01 -2.9515E-02... 

PC15 PHOSPHORUS PENTACHLORIDE 25.701 4.7099E-01 -7.8406E-04 5.6105E-07 -1.4442E-10 100 1500 gas... 

The largest class of molecules to violate the octet rule consists of species in which the central atom is surrounded by more than four pairs of valence electrons. Typical molecules of this type are phosphorus pentachloride, PC15, and sulfur hexafluoride, SF6. The Lewis structures of these molecules are... 

Phosphorus Pentachloride (Phosphoric chloride, Phosphorus perchloride). PC15, mw 208.27 white to pale yel, fuming, deliq, cryst mass pungent, unpleasant odor mp (under press) 148° ordinarily sublimes without melting at 160—165°. Sol with decompn and liberation of much heat in w or ale sol in C disulfide or tetrachloride. Can be prepd by the action of chlorine on P or P trichloride (Refs 9 10)... 

Phosphorus trichloride, PCI, and phosphorus pentachloride, PC15, are the two most important halides of phosphorus. The former is prepared by direct chlorination... 

An interesting feature of phosphorus pentachloride is that it is an ionic solid of tetrahedral PC14+ cations and octahedral PC16 anions, but it vaporizes to a gas of trigonal bipyramidal PC15 molecules (see Section 2.10). Phosphorus pentabromide is also molecular in the vapor and ionic as the solid but, in the solid, the anions are simply Br ions, presumably because six bulky Br atoms simply do not fit around a central P atom. 

An alternative method of synthesis of N3P3Cl6 has been developed recently, based on the reaction of tris (trimethylsilyl) amine and phosphorus pentachloride (40). This reaction either preferentially leads to the formation of N3P3C16 or to an N-silylated phosphoranimine intermediate C13P - NSiMe3, depending on the reaction conditions used. Thus the reaction between tris (trimethylsilylamine) and PC15 in methylene chloride at 40° C affords a mixture of cyclo and linear phosphazenes, which has been shown by an NMR analysis to contain up to 76% of N3P3C16 (Eq. 2). 

Other reagents that have been used to effect the dehydration of ureas to carbodiimides are alkyl chloroformates (for thioureas) [46], phosgene [47], phosphorus oxychloride [48], and phosphorus pentachloride [38, 49]. Di-chlorocarbodiimides have been shown to be intermediates when COCl2 or PC15 reacts with ureas (Eq. 13). If R1 and R3 are H, then the intermediate... 

Phosphorus pentachloride is an ionic solid consisting of PC14+ cations and PC16 anions, and it sublimes at 160°C to a gas of PCI, molecules. The Lewis structures of the polyatomic ions and the molecule are shown in (33). Although the cation is a polyatomic ion in which the P atom does not need to expand its valence shell, in the anion the P atom has expanded its valence shell to 12 electrons, by making use of two of its 3d-orbitals. In PC15, the P atom has expanded its valence shell to 10 electrons by using one 3d-orbital. 

Because they are readily available from a number of synthetic reactions, carboxylic acids are the most common starting materials for the preparation of the other members of this family. Conversion of a carboxylic acid to an acyl chloride provides access to any of the other derivatives because the acyl chloride is at the top of the reactivity scale. Bui how can the acyl chloride be prepared from the acid when the acid is lower on the reactivity scale This can be accomplished by using an even more reactive compound to drive the equilibrium in the desired direction. The reagent that is employed in the vast majority of cases is thionyl chloride, SOCl2. Phosphorus trichloride, PC13, and phosphorus pentachloride, PC15, are also used occasionally. Examples are provided in the following equations ... 

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