Pyridinium Tribromide Synthesis Essay


(selective brominating reagent for ketones,2 acetals,3 alkenes,4 activated phenols,5 anilines,6 and nitrogen heterocycles;7 mild oxidation/dehydrogenation reagent8)

Alternate Names: PHBP; pyridinium bromide perbromide; pyridinium perbromide; pyridinium tribromide.

Physical Data: mp – °C (% Br), mp – °C (47% Br),7  °C (50% Br).9

Solubility: sol acetic acid, methanol, ethanol, n-butanol, THF, ether (wet); insol water, carbon tetrachloride, ethyl bromide, ether (anhydrous), benzene, toluene, ligroin, petroleum ether.9

Form Supplied in: red-orange solid, generally 90–97% pure; commercially available.

Analysis of Reagent Purity: iodometric titration.10

Preparative Method: from pyridine, 48% hydrobromic acid, and bromine.1, 7 The bromine content varies depending on the method of preparation.7, 11

Purification: recrystallization from ethanol.12 Recrystallization from acetic acid reduces the bromine content. Pure material can be obtained by adding bromine to impure material until a paste is produced. Excess bromine is allowed to evaporate, giving pure material, mp  °C (50% Br).9

Handling, Storage, and Precautions: protect from moisture, strong acids, and bases. This toxic reagent must be used in a fume hood.

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