Phosphorus tribromide, conversion

The conversion of an aliphatic carboxylic acid into the a-bromo- (or a-chloro ) acid by treatment with bromine (or chlorine) in the presence of a catal3rtic amount of phosphorus tribromide (or trichloride) or of red phosphorus is known as the Hell-Volhard-Zelinsky reaction. The procedure probably involves the intermediate formation of the acyl halide, since it is known that halogens react more rapidly with acyl haUdes than with the acids themselves ... 

Note 1. The concentration of the aqueous HBr solution is increased by conversion of phosphorus tribromide with water. If available, a corresponding amount of gaseous HBr can be introduced into the 48% solution at 0°C. 

Phosphorus pentachloride, for conversion of pentaacetylgluconic add to add chloride, 41, 80 for oxidation of cycloheptatriene to tropylium fluoborate, 43, 101 with cyanoacetic acid, 41, 5 Phosphorus tribromide, reaction with 1.5-hexadien-3-ol, 41, 50 Phthalic anhydride, reaction with L-phenylalanine to yield N-phthalyl-L-phenylalanine, 40, 82 Phthalic monoperacid, 42, 77 N-Phthalyl-i.-alanine, 40, 84 N-Phthalyl-/3-alanine, 40, 84 N-Phthalylglycine, 40, 84 N-Phthalyl-l-/5-phenylalanine, 40, 82... 

As stated earlier, all other forms of phosphorus can be made from white phosphorus. Thus, heating white phosphorus first at 260°C for a few hours and then at 350°C gives red phosphorus. The conversion is exothermic and can become explosive in the presence of iodine as a catalyst. When a solution of white phosphorus in carbon disulfide or phosphorus tribromide is irradiated the scarlet red variety is obtained. 

Phosphorus pentachloride, for conversion of pentaacetylgluconic add to acid chloride, 41, 80 with cyanoacetic add, 41, 5 Phosphorus tribromide, reaction with... 

Fig. Conversion of an alcohol to an alkyl halide using (a) thionyl chloride (b) phosphorus tribromide.

R—OH + SOCl2 — or PBr3 — R —Cl or R—Br SNlor Sm2 thionyl chloride, phosphorus tribromide, and phosphorus triiodide provide a good one-step procedure for conversion of an alcohol to an alkyl chloride, bromide, or iodide... 

The conversion of a carboxylic acid to its halide is usually accomplished by thionyl chloride or phosphorus halides. Phosphorus trichloride and glacial acetic acid give acetyl chloride (67%). The other product is phosphorus acid. Phosphorus pentachloride is converted to phosphorus oxychloride (b.p. 103°), from which the acyl halide is sometimes separated with difficulty. This reagent, however, finds use in the preparation of certain higher-molecular-weight halides. .. Most acyl bromides are made from phosphorus tribromide. ... 

Light Red Amorphous Phosphorus, sometimes called scarlet phosphorus, is another allotropic form. It is prepared by dissolving yellow phosphorus in phosphorus tribromide and boiling the solution. The new modification separates out of the solution as a finely divided, amorphous powder. Like dark red phosphorus, the scarlet form is not poisonous. It is, however, more chemically reactive than the former owing to its more finely divided condition. Conversion of scarlet into dark red phosphorus may be brought about by continued... 

Bromomorphide, believed to be analogous to [vi], is formed by the action of phosphorus tribromide on morphine [82], A mixture of a-, /3-, and y-isomorphines, but no morphine, is obtained by the hydrolysis of the lialogenomorphides [454-53,463-4,82], The conversion of morphine through the chloride to isomers of morphine resembles the geraniol-liimlool conversion [465, 466]. The halogenomorphides are discussed 111 detail in Chapter VIII. 

A synthetic example of an Sn2 reaction is the conversion of 90 to a tertiary bromide with phosphorus tribromide. Subsequent reaction with the sodium salt of thiophenol gave an Sis(2 displacement to 91 in Ito s synthesis of neocembrene. l... 

R = CH2CH2NH2, Ri = CH2OH). Conversion to the benzyl bromide with phosphorus tribromide and alkaline cyclization gave. CV (R, Ri = CH3 R2 = 0CH3 NH instead of NCH3). iV -Methylation with formaldehyde and formic acid completed the synthesis (110). 

Cbzo-DL-valine, N,N -dicbzo-L-lysine, N-Cbzo-sarcosine, N-Cbetho-anthranilic acid, and N-Cbzo-anthranilic acid) with phosphorus tribromide at room temperature resulted in their conversion to the corresponding N-carboxy-a-amino acid anhydrides in high yields (60-88%) [858]. 

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