Phosphoryl bromide

In view of the high price and other difficulties associated with the use of phosphoryl bromide, the transhalogenation of 2-chloro- and 2-chloro-4,6-dimethyl-pyrimidine (919) by treatment with inexpensive phosphorus tribromide to give their bromo analogues in >50% yield, assumes potential importance as a general method (67JCS(C)1204). 

Using Phosphorus Tribromide, Phosphorus Pentabromide, or Phosphoryl Bromide... 

Lithium chloride Phosphorus oxybromide and oxychloride (phosphoryl bromide and chloride)... 

To establish which percentage of the label is present on the ring nitrogen and which on the amino group, the amino compound was converted by acid hydrolysis into 4-phenylpyrimidin-6(l//)-one, which was subsequently converted into 6-bromo-4-phenylpyrimidine (18a) by treatment with phosphoryl bromide (Scheme 11.12). If the content of the bromo compound 18a contains y%, the percentage of the 6-halogeno compound that reacts according to the Sn(ANRORC) mechanism can be calculated, i.e., (y X 100%. 

Heating 1-phenyl- and 5-methy 1-1-phenyl-1,2,4-triazol-3-ones with phosphoryl bromide gave 45% yields of the 3-bromo derivatives (75BSF647). 

Quinoxaline-2,3-dione is converted into 2,3-dichloroquinoxaline by phosphoryl chloride142 or phosphorus pentachloride.143 2,3-Dibromo-quinoxaline is similarly obtained using phosphoryl bromide in dimethyl-aniline.144 Quinoxalin-2-one undergoes ring contraction to 2-methyl-benzimidazole (134) with hydrazine145 however, quinoxaline-2,3-dione gives 3-hydrazino-2-quinoxalinone.145 Quinoxalin-2-one yields a 3-p-dimethylaminophenyl derivative with 7V,N-dimethylaniline (in AcOH, with NH4N03), and a 3-(indol-3-yl) derivative with indole.146... 

Arsenic triiodide also dissolves, the saturated solution at 15° C. having density 3-661. Other soluble halides are potassium bromide, anhydrous ferric and aluminium chlorides 6 and tetramethyl ammonium iodide but the iodides of rubidium, cadmium, manganese and cobalt, also mercuric and stannic iodides, and cobalt and stannic bromides, are insoluble or only very slightly soluble in arsenic tribromide. The liquid also dissolves phosphoryl bromide and, very slightly, ammonium thiocyanate. In the mixed solutions of halides, the components may react chemically (cf. p. 106), but such is not always the case for example, with antimony tribromide a continuous series of solid solutions is formed.7... 

He found that with ordinary commercial red phosphorus with 98 per cent, phosphorus, there dissolved 0-056 and 0-108 per cent, of phosphorus in respectively 10 and 42 hrs., and with a finely-divided sample 0-092 and 0-116 percent, phosphorus in 10 and 20 hrs. respectively. R. Schenck found that 100 grms. of phosphorus tribromide dissolved 0-2601 grm. of scarlet phosphorus at 172°, and 0-3634 grm. at 184°. E. Baudrimont showed that yellow phosphorus does not attack phosphoryl bromide at the b.p. L. Rosenstein found that soln. of arsenates, and arsenic, antimony, or bismuth salts are not reduced by boiling with red phosphorus but W. Finkelstein found that a nitrobenzene soln. of arsenic trichloride is reduced by yellow phosphorus and arsenic is deposited. 0. Ruff observed that phosphorus reacts with antimony trichloride in the presence of a little aluminium chloride. F. E. Brown and J. E. Snyder observed that vanadium oxytrichloride is without action on red or white phosphorus. 

J. H. Gladstone found that when phosphorus pentabromide is oxidized by exposure to air it deliquesces, forming a red syrupy liquid of phosphoryl bromide,... 

A. Michaelis did not succeed in making pyrophosphoryl bromide, P203Br4, by the action of nitrogen peroxide or trioxide on phosphorus tribromide—the products are phosphorus pentoxide and phosphoryl bromide. T. E. Thorpe and A. E. H. Tutton said metaphosphoryl bromide, P02Br, is produced by the action of bromine on phosphorous oxide as indicated above, and it remains as a residue after the phosphoryl bromide has been removed by distillation. 

The conversion of a tautomeric 1,5-naphthyridinone into the corresponding chloro- or bromo-l,5-naphthyridine is usually done by heating for several hours with neat phosphoryl chloride or phosphoryl bromide, respectively. A mixture of phosphoryl chloride and phosphorus pentachloride has been used for a few difficult cases. In addition, exceptional reactions have been reported in which a nontautomeric /V-alkyl-1,5-naphthyridinone or a hydroxymethyl-1,5-naphthyridine was used successfully as substrate. The following examples illustrate the foregoing possibilities. 

Note The chlorolysis of naphthyridinones or naphthyridinoles is usually done with neat phosphoryl chloride to which may be added phosphorus pentachlor-ide or dimethylformamide in difficult cases corresponding bromolysis is achieved by the use of phosphoryl bromide and the chlorolysis of (extra-nuclear) hydroxyalkyl-1,8-naphthyridines may be done with thionyl chloride with or without added zinc chloride. Typical examples of these procedures are given here. 

Note At least in simple cases, the Meissenheimer reaction appears to be unsatisfactory for the production of halogeno-l,8-haphthyridines. Thus 1,8-naphthyridine 1-oxide with phosphoryl chloride gave a difficult-to-separate mixture of 2-, 3-, and 4-chloro-l,8-naphthyridine (in ratio 36 7 57) 225 phosphoryl bromide and bromine/acetic acid both gave even worse mixtures... 

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