Physical Properties:

Pyridinium tribromide (PTB, CAS 39416-48-3) is a dark red/brown solid, highly efficient brominating agent used in organic synthesis to substitute for volatile liquid bromine. It is a selective agent for alkene and aromatic bromination, characterized by a melting point of 127–137∘C and formula 𝐶5𝐻6𝐵𝑟3𝑁. The compound is hygroscopic and causes severe skin/eye burns.

Key Chemical & Physical Properties

Molecular Formula: 𝐶5𝐻6𝐵𝑟3𝑁

Molecular Weight: 319.82 g/mol

Appearance: Red to orange/brown powder, crystals, or chunks

Melting Point: 127–137∘C

Solubility: Soluble in polar solvents like methanol; decomposes in water

Stability: Stable but hygroscopic, necessitating storage in a cool, dark, dry place

Density: ∼2.96g/cm3

Uses and Characteristics

Brominating Agent: Used for the selective bromination of ketones, alkenes, and aromatic compounds.

Advantages: It is easier to handle than liquid molecular bromine (𝐵𝑟2), as it is a solid, stable at room temperature, and less volatile.

Reactivity: Acts as a solid source of bromine, generally providing good selectivity in synthesis.

Safety and Handling

Hazard Class: UN 3261 (Corrosive solid, acidic, organic).

Safety Phrases: Causes severe skin burns and eye damage.

Handling: Must be used in a well-ventilated area with appropriate protective equipment.

Sensitive: Lachrymatory

Pyridinium tribromide (PTAB), with the CAS number 39416-48-3, is a versatile brominating agent in organic synthesis. It is often referred to by several synonyms related to its chemical composition, which consists of a pyridinium cation and a tribromide anion (𝐶5𝐻5𝑁𝐻+𝐵𝑟−3).

Primary Synonyms

Pyridinium bromide perbromide (commonly used name)

Pyridine hydrobromide perbromide

Pyridinium perbromide

Pyridine perbromide hydrobromide

Other Technical/Chemical Synonyms

• Hydrogen tribromide, compd. with pyridine (1:1)
• Pyridine, (hydrogen tribromide)
• Pyridine, bromide, hydrogen salt (1:3)
• NSC 61191
• PHBP (Abbreviation for Pyridinium HydroBromide Perbromide)
• 2l3-tribromane–pyridine (1/1)

Commonly Associated Trade/Product Names

• Pyridinium tribromide, technical grade
• Pyridinium bromide-perbromide for synthesis

Pyridinium tribromide (PTB, CAS 39416-48-3) is a stable, solid, and easy-to-handle brominating agent used in organic synthesis. Its primary applications include the selective 𝛼-bromination of ketones, phenols, and ethers. It is also employed for adding bromine across double or triple bonds, oxidizing alcohols, and synthesizing pharmaceutical intermediates, including 𝛽-blockers.

Key Uses and Applications

• Selective Bromination: Used as a milder alternative to molecular bromine (

𝐵𝑟2) for the bromination of unsaturated compounds (alkenes and alkynes) to form vicinal dibromides.

• Alpha-Bromination of Carbonyls: It efficiently brominates ketones at the 𝛼-position, a key step in organic synthesis, for example, the bromination of 3-ketosteroid to 2,4-dibromocholestanone.
• Pharmaceutical Synthesis: Extensively applied in the synthesis of active pharmaceutical ingredients (APIs), including 𝛽-adrenergic blocking agents (beta-blockers) to treat heart conditions, according to CymitQuimica and nordmann.global.
• Oxidation Reactions: PTB can be used for the oxidation of alcohols, aldehydes, and ketones to their corresponding carbonyl bromides, notes NINGBO INNO PHARMCHEM CO.,LTD..
• Agrochemicals: Used in the production of agricultural chemicals, including specific herbicide intermediates.
• Organic Synthesis Reagent: Used for the 𝛼-thiocyanation of ketones and in various cyclization reactions Advantages

• Stable Solid: Unlike liquid bromine, it is a stable solid, making it safer and easier to weigh and handle, especially for small-scale lab reactions,
• Selective: Allows for precise bromination without damaging other parts of the molecule, which is critical in delicate synthesis.

Physical Properties

Formula: 𝐶5𝐻6𝐵𝑟3𝑁 or 𝑃𝑦⋅𝐻𝐵𝑟3).

Appearance: Yellowish solid.

Solubility: Soluble in common organic solvents like dichloromethane, chloroform, and ether.