Phosphorus tribromide, preparation

The hydrolysis of phosphorus tribromide or triiodide is used in the preparation of hydrogen bromide and hydrogen iodide respectively ... 

Substituted 5-hydroxythiazoles (267b), Rj = alkylmercapto, acyl-amino, and sec-amino, are prepared by cydization of N-thioacyl-amino acids (266) with phosphorus tribromide or acetic anhydride (Scheme 137) (317, 350). i en the cydization of 266, R2 = H, is carried out with acetic anhydride in the presence of benzaldehyde (317, 325) or ethylformate (317), the benzylidene (268), R2=Ph, Rj = SR or CH2Ph, or 4-ethoxymethylene (268), Rj = SR and R2 = OEt, derivative is obtained directly (Scheme 138). 

Ethylene bromohydrin has been prepared by the reaction between ethylene glycol and hydrobromic acid and phosphorus tribromide. It has also been prepared by the direct addition of hypobromous acid to ethylene, and by the reaction between ethylene and dilute bromine water. With ethylene oxide now available at a reasonable price, the method described is probably the best because of the high yields and the convenience of reaction. 

Glycerol a,7-dibromohydrin has been prepared from glycerol and phosphorus tribromide from glycerol and bromine from glycerol, red phosphorus, and bromine. ... 

The temperature must be raised slowly to avoid formation of spontaneously inflammable hydrides of phosphorus whict will ignite and destroy the preparation. A similar result occur if the phosphorus tribromide is added at 170°. 

Pentaerythrityl bromide has been prepared by the action of phosphorus tribromide on pentaerythritol, - and of an acetic acid solution of hydrobromic acid on pentaerythritol tetraacetate. The iodide has been prepared by the action of red phosphorus and hydriodic acid on pentaerythritol and by treating the bromide with sodium iodide in acetone. ... 

Alkyl halides are such useful starting materials for preparing other functional group types that chemists have developed several different methods for converting alcohols to alkyl halides. Two methods, based on the inorganic reagents thionyl chloride and phosphorus tribromide, bear special mention. 

Preparation of 2-Bromo-3-Hexyne A solution of 13B g of 3-hexyne-2-ol and 9 g of pyridine in 13B ml of anhydrous ether was treated with 175 g of phosphorus tribromide, added dropwise over a period of about 20 minutes at a temperature of about -10°C. The reaction mixture was permitted to come to room temperature while stirring for about 3 hours, and was then heated to refluxing for about 1 hour. After cooling, the reaction mixture was poured over about 50 g of crushed ice. A two-phase system formed, and the ether layer was separated, washed with dilute sodium bicarbonate solution, dried over anhydrous potassium carbonate and fractionally distilled. The 2-bromo-3-hexyne formed in the reaction was collected at 75°C at the pressure of 50 mm of mercury. 

Acid chlorides are prepared from carboxylic acids by reaction with thionyl chloride (SOCl2), as we saw in the previous section. Similar reaction of a carboxylic acid with phosphorus tribromide (PB ) yields the acid bromide. 

Tetrahydroimidazo[5,l-c][l,2,4]triazine 474 was prepared (79KGS1540) by treating imidazole derivatives 472 or 473 with hydrazine. Compound 473 was obtained by reaction of the respective imidazole with 1,2-dibromoethane or by the reaction of the alcohol derivative 471 with phosphorus tribromide. On the other hand, chlorination of471 with thionyl chloride gave 472 (Scheme 100). 

The six isomeric tris(methylthienyl)phosphines, e.g. (2), have been prepared by the reaction of methylthienyl-lithium derivatives with phosphorus tribromide. ... 

The new family of phospholes with 2,4,6-trialkylphenyl substituent on the phosphorus atom show, in many respects, a special reactivity. Due to the flattening of the P-pyramid, the arylphospholes exhibit aromaticity and hence underwent Friedel-Crafts reactions. The regioselective functionalization through reaction with phosphorus tribromide gave a variety of phospholes with an exocyclic P-moiety. Novel phosphole platinum and rhodium complexes were prepared and a part of them was tested in hydroformylation reactions. 

Tetrahydrofurfuryl bromide has been obtained in low yields by the action of hydrobromic acid, or of phosphorus tribromide, on the corresponding alcohol.1 The yield is improved markedly by use of phosphorus tribromide and pyridine.2 3 The bromide has also been prepared by the action of potassium hydroxide on 4,5-dibromopentanol-l.4... 

Cinnamyl bromide has been prepared from cinnamyl alcohol by the action of hydrogen bromide in cold acetic acid2 and of phosphorus tribromide in boiling benzene.3 It has also been... 

An attempt to prepare 1 -bromo-2-fluoroethane by the partial fluorination of ethylene dibromide by means of antimony trifluoride was not very successful. The compound was best prepared by the action of phosphorus tribromide on F.E.A. The compound was relatively non-toxic and the bromine atom rather unreactive, but considerably more reactive than the chlorine atom in chlorofluoroethane. For example, bromofluoroethane was readily converted by means of potassium thiocyanate into 2-fluoroethyl thiocyanate. As a lethal inhalant the toxicity of the thiocyanate was inferior to that of M.F.A. Toxicity by injection, however, appeared to be higher. 

Phosphorus continued) tribromide, preparation of, 7 14 trichloride, reactions with silylphosphanes, 31 189-190... 

The methods for the preparation of bromotrimethylsilane include the treatment of hexamethyldisiloxane with bromine reagents such as phosphorus tribromide,1,2 2,2,2-tribromo-l, 3,2 /5-benzodioxaphosphole (catechyl phosphorus tribromide),2 and aluminium tribromide,3 the yields being in the range from 73 to 87%. A further method4 shows that bromotrimethylsilane can be obtained from aminosilanes and hydrobromic acid, but the yield (55%) is lower than in the former methods. Other methods involve the use of expensive reagents, such as hexamethyldisilane, l,4-bis(trimethylsilyl)-2, 5-cyclohexadiene, and 1,4-dihydro-l, 4-bis(trimethylsilyl)naphthalene.5 Finally, some alternative procedures have been developed for its in situ preparation.5... 

Fig. 101. Setup for preparing phosphorus tribromide from red phosphorus...

Preparation of Phosphorus Tribromide by Reacting White Phosphorus with Bromine. (Perform the experiment in a ume cupboard ) To prepare phosphorus tribromide, one must have purified white phosphorus and dry bromine. 

Transfer the prepared phosphorus tribromide into a weighed drawn out test tube and seal it (wear eye protection . Weigh the ampoule together with the remaining parts of the test tube. Calculate the yield in per cent. 

Both reactants in the Williamson ether synthesis usually originate in alcohol precursors. Sodium and potassium alkoxides are prepared by reaction of an alcohol with the appropriate metal, and alkyl halides are most commonly made from alcohols by reaction with a hydrogen halide (Section 4.7), thionyl chloride (Section 4.13), or phosphorus tribromide (Section 4.13). Alternatively, alkyl p-toluenesulfonates may be used in place of alkyl halides alkyl p-toluenesulfonates are also prepared from alcohols as their immediate precursors (Section 8.14). 

Halogen atoms have been placed at C-6 of substituted 6-deoxy-hexoses by a variety of interesting ways, and the products provide potential routes to 6-deoxyhexoses. Helferich and coworkers 4 reported a low yield of methyl 6-chloro-6-deoxy-a-D-glucoside which they prepared by reaction of the (suitably protected) corresponding 6-trityl ether with phosphorus pentachloride. Sinclair 44 has provided a convenient procedure for the preparation of the 6-chloro derivative in yields of 30-35% by allowing methyl a-D-glucopyranoside to react with sulfur monochloride, SjClj, in N,/V-dimethylformamide. A much better yield (73%) of the 6-bromo derivative was reported1 in the reaction of methyl 2,3,4-tri-O-benzoyl-6-O-trityl-a-D-altroside with phosphorus tribromide and bromine. 

Fifty grams of phosphorus (V) bromide are first prepared, either by allowing 18,5g of bromine to drop slowly into 31.5g of ice-cold phosphorus tribromide, or by dropping 46.5g of bromine dropwise on 3.6g of dry red phosphorus. Either reaction is conducted in a stout pressure bottle of about 500ml capacity moisture must be carefully excluded. 

Phosphorus oxybromide reacts slowly with water to yield orthophosphoric and hydrobromic acids. It dissolves readily in many organic solvents such as ether, benzene, and carbon tetrachloride. Because the bromide decomposes readily at high temperatures, it should always be melted in a hot water bath (m.p. 55 56°C), never with a flame. Prepared as described, the product contains traces of phosphorus tribromide which can be removed only by 6-fold high-vacuum distillation. 

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