Phosphorus pentahalide

Phosphorus pentachloride, 79 40, 42-44 end use of chlorine, 6 135t sodium reactions with, 22 766 Phosphorus pentafluoride, 79 33 Phosphorus pentahalides, 79 31-33 Phosphorus pentoxide, 79 49, 69. See also Phosphorus(V) oxides as cellulose solvent, 77 272 in hydrogen fluoride manufacture, 74 11 vapor of, 79 49... 

Various structures have been found for phosphorus pentahalides ... 

The conversion of a 1,6-naphthyridinone into the corresponding halogeno-1, 6-naphthyridine is usually done by refluxing with phosphoryl chloride or bromide, with or without the addition of a tertiary base alternatively, a phosphorus pentahalide can be used but additional C-halogenation may result. Nontautomeric... 

The classical route to chloropyrazines is by treatment of a hydroxy-pyrazine with phosphoryl chloride bromopyrazines are similarly prepared by using phosphoryl bromide, phosphorus tribromide, or a mixture of both. Thus, treatment of hydro xypyrazine with phosphoryl chloride gives chloropyrazine in 92% yield,147 and treatment of the hydroxy compound with a mixture of phosphoryl bromide and phosphorus tribromide gives bromopyrazine in 58% yield.266 The use of phosphorus pentahalides frequently leads to substitution products (Scheme 22) for example, when hydroxypyrazine is treated with a mixture of phosphoryl bromide and phosphorus pentabromide both monobromo- and 2,6-dibromopyrazines are formed.287,268 Bromina-tion of hydroxypyrazine with bromine in the presence of small... 

Trimethylsilyl halides will exchange halogen with Me3N BX3 adducts (9) and BF4" (80). Phosphorus pentahalides (9, 13), A12C16 (9), and AsC13 (9) act similarly on amine adducts. 

Examples of molecules in which the central atom contains an expanded octet are the phosphorus pentahalides and sulfur hexafluoride. 

Phosphorus pentahalides PX5 (X = Cl and Br) are mild oxidants which were used already more than a century ago to oxidize platinum black to bridged dimers [Pt2(yU2-X)2X2(PX3)2] [235a]. Oxidative chlorination of Pt to PF complexes by PCI5 is classic, and compares favorably with use of CI2 which is common to carry out this reaction [235b]. 

Cholesteryl methyl ether is converted into 3)8-chloro- or 3) -bromo-cholest-5-ene by the appropriate phosphorus pentahalide in the presence of boron trifluoride etherate. ... 

For the above reasons nitrogen forms many compounds of types not formed by other elements of this group, and for this reason we deal separately with the stereochemistry of this element. For example, the only compounds of N and P which are structurally similar are the molecules in which the elements are 3-covalent and the phosphonium and ammonium ions. There are no nitrogen analogues of the phosphorus pentahalides, and there is little resemblance between the oxygen compounds of the two elements. Monatomic ions of nitrogen and phosphorus are known only in the solid state, in the salt-like nitrides and phosphides of the more electropositive elements. The multiple-bonded azide ion, N3, is peculiar to nitrogen. 

Reaction with alcohols and phenols. Horner and co-workers introduced use of the reagents for the preparation of alkyl and aryl halides from alcohols or phenols, and Wiley and co-workers established that the reagents have considerable advantage over phosphorus pentahalides in the C—OH—C—X conversion and discussed the mechanism. For the preparation of n-butyl bromide the Wiley group added bromine under nitrogen to a solution of n-butanol and triphenylphosphine in dimethyl-formamide until 2 drops persisted in giving the solution an orange tint. Volatile... 

The halides and oxyhalides of some nonmetals hydrolyze (react with water) to produce two acids a (binary) hydrohalic acid and a (ternary) oxyacid of the nonmetal. Phosphorus trihalides react with water to produce the corresponding hydrohalic acids and phosphorous acid, a weak diprotic acid, whereas phosphorus pentahalides give phosphoric acid and the corresponding hydrohalic acid. 

The classical synthesis of imidoyl chlorides involves the reaction of N-substituted carboxylic acid amides with phosphorus pentahalides. Wallach and his students (288-292 1876-1882 investigated this reaction... 

If an excess of phosphorus pentahalides is used on aliphatic carboxylic acid amides, having a-hydrogens, further halogenation occurs. For example, the reaction of propionic acid ethylamide (XV) with 3 equivalents of phosphorus pentachloride yields the imidoyl chloride XVI, which can also be obtained from a,a-dichloropropionic acid ethylamide (XVII) and one equivalent of phosphorus pentachloride (5 ). 

Similarly, reaction of cyclic imides with phosphorus pentahalides should afford the corresponding dihaloimidoyl halides. In 1882 Bernheimer ( ) treated glutarimide with phosphorus pentachloride, and he assigned the imidoyl chloride structure XLIV to the reaction product. However, it was later shown that the compound was 2 3,6-trichloropyridine (XLV) ( ). 

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