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Pyridinium tribromide, also known as pyridinium bromide perbromide (PHPB), CAS No. 39416-48-3, has the molecular formula C5H6Br3N and a molecular weight of 319.82. It is an orange-red to reddish-brown crystalline powder, melting at approximately 127–133 °C with decomposition. Composed of a pyridinium cation and a tribromide anion, it decomposes in water but is soluble in methanol, dichloromethane, and chloroform, making it a solid brominating reagent that combines high activity with excellent controllability.
Unlike highly volatile and corrosive elemental bromine, pyridinium tribromide releases electrophilic bromine slowly and controllably in solid form, allowing precise weighing and dosing. As the reaction proceeds, its color fades from red, giving an unmistakable visual endpoint. Its most classic use is the α-bromination of ketones: a ketone first enolizes, then undergoes electrophilic addition with the bromine released by the reagent, and deprotonation affords the α-bromoketone. The general scheme can be written as R-CH2-CO-R’ + PyHBr3 → R-CHBr-CO-R’ + PyHBr + HBr. This process is highly selective and effectively suppresses over-bromination. With an active bromine content of about 50%, it reacts efficiently in mild solvents such as acetic acid without strongly corrosive conditions; the pyridine hydrobromide formed is largely a solid and is easy to remove, reducing the waste burden.
In terms of applications, it is also widely used for the selective bromination of phenols and aryl ethers, as well as the α-thiocyanation of ketones. It is a key raw material for synthesizing pharmaceutical intermediates such as β-blockers, and can also serve as an organic analytical reagent, covering the entire range from milligram-scale screening to kilogram-scale scale-up. These α-brominated products can be further substituted to yield numerous pharmaceutically active molecules, making it an important link between basic synthesis and pharmaceutical scale-up.
It is worth noting that this product is sensitive to moisture and light, and should be stored sealed, protected from light, and kept cool at 2–10 °C. Shunxiang Pharmaceutical has been deeply engaged in fine chemicals for many years, offering a long-term, stable supply of high-purity pyridinium tribromide with strict batch-by-batch quality control and cool, moisture-protected logistics throughout, providing reliable back-end support for your R&D and scale-up. We welcome your inquiries — let us make every bromination reaction safer and more precise with Shunxiang Pharmaceutical.