Phosphorus tribromide reaction with alcohols

Phosphine(s), chirality of, 314 Phosphite, DNA synthesis and, 1115 oxidation of, 1116 Phospholipid, 1066-1067 classification of, 1066 Phosphopantetheine, coenzyme A from. 817 structure of, 1127 Phosphoramidite, DNA synthesis and, 1115 Phosphoranc, 720 Phosphoric acid, pKa of, 51 Phosphoric acid anhydride, 1127 Phosphorus, hybridization of, 20 Phosphorus oxychloride, alcohol dehydration with. 620-622 Phosphorus tribromide, reaction with alcohols. 344. 618 Photochemical reaction, 1181 Photolithography, 505-506 resists for, 505-506 Photon, 419 energy- of. 420 Photosynthesis, 973-974 Phthalic acid, structure of, 753 Phthalimide, Gabriel amine synthesis and, 929... 

Reaction of alcohols with phosphorus tribromide (Section 4 13) As an alternative to converting alco hols to alkyl bromides with hydrogen bromide the inorganic reagent phosphorus tribromide is some times used... 

Reaction with phosphorus trihalides (Section 4 13) Phosphorus trichloride and phosphorus tribromide convert alcohols to alkyl halides... 

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). 

Another general method for converting alcohols to halides involves reactions with halides of certain nonmetallic elements. Thionyl chloride, phosphorus trichloride, and phosphorus tribromide are the most common examples of this group of reagents. These reagents are suitable for alcohols that are neither acid sensitive nor prone to structural rearrangement. The reaction of alcohols with thionyl chloride initially results in the formation of a chlorosulfite ester. There are two mechanisms by which the chlorosulfite can be converted to a chloride. In aprotic nucleophilic solvents, such as dioxane, solvent participation can lead to overall retention of configuration.7... 

In a similar vein, the keto bridge in 5 can be replaced by oxygen with retention of activity. Reduction of acetophenone derivative 19 by means of sodium borohydride leads to the corresponding alcohol (20). Reaction with phosphorus tribromide with cyanide gives... 

In a 2-1. three-necked flask, fitted with a mechanical stirrer (Note 1), a reflux condenser, and a dropping funnel, is placed 630 g. (670 cc., 7 moles) of /3-ethoxyethyl alcohol (Note 2). The stirrer is started, and 600 g. (210 cc., 2.2 moles) (Note 3) of phosphorus tribromide is added from the dropping funnel over a period of one and one-half to two hours. The temperature is permitted to rise until the reaction mixture refluxes gently. 

Reaction with phosphorus trihalides Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide (Refer Unit 10, Class XII). 

The mechanism for the reactions with phosphorus halides can be illustrated using phosphorus tribromide. Initial reaction between the alcohol and phosphorus tribromide leads to a trialkyl phosphite ester by successive displacements of bromide. The reaction stops at this stage if it is run in the presence of an amine which neutralizes the hydrogen bromide that is formed.9 If the hydrogen bromide is not neutralized the phosphite ester is protonated and each alkyl group is successively converted to the halide by nucleophilic substitution by bromide ion. The driving force for cleavage of the C—O bond is the... 

The reaction of phosphorus tribromide with the alcohol above has been reported by Marvel to give the analogous bromide. The use of phosphorus trichloride did not yield the chloride [80]. 

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). 

Exercise 15-21 Write the steps that could plausibly take place in the reaction of a primary alcohol with phosphorus tribromide in the presence of the weak base pyridine to give an alkyl bromide. 

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