Carbonyl bromide is a chemical compound with the formula COBr₂. It is also known by its systematic IUPAC name, dibromomethanone, or more commonly, bromophosgene. It is the bromine analog of phosgene (COCl₂), sharing similar chemical reactivity and hazards but typically being less stable.
Properties
Carbonyl bromide is a colorless to light yellow fuming liquid at room temperature, possessing a very strong, pungent, and highly irritating odor. Its boiling point is approximately 64-65 °C, and it is relatively volatile.
- Molecular Structure: The molecule has a trigonal planar geometry around the central carbon atom, which is double-bonded to an oxygen atom and single-bonded to two bromine atoms.
- Reactivity: Carbonyl bromide is highly reactive. It slowly hydrolyzes in the presence of water or moisture to produce hydrogen bromide (HBr) and carbonic acid (H₂CO₃), which further decomposes into carbon dioxide (CO₂) and water (H₂O). COBr₂ + 2 H₂O → H₂CO₃ + 2 HBr → CO₂ + 2 HBr + H₂O It acts as an electrophilic carbonylating agent and can react with nucleophiles such as alcohols to form carbonates or with amines to form ureas, though typically with more vigor than phosgene.
Synthesis
Carbonyl bromide can be synthesized through various methods, predominantly:
- From Carbon Monoxide and Bromine: The most common industrial synthesis involves the direct reaction of carbon monoxide (CO) with bromine (Br₂) in the presence of a suitable catalyst, such as activated charcoal, often at elevated temperatures. CO + Br₂ → COBr₂
- From Phosgene and Hydrogen Bromide: It can also be prepared by the reaction of phosgene (COCl₂) with hydrogen bromide (HBr), leading to a halogen exchange reaction, though this is less frequently used for large-scale production.
Applications
Due to its high reactivity and the presence of two reactive bromine atoms and a carbonyl group, carbonyl bromide finds niche applications in organic synthesis:
- Bromination and Carbonylation Agent: It serves as a versatile reagent for introducing a carbonyl group and/or bromine atoms into organic molecules. It can be used in the synthesis of carbonates, carbamates, and various brominated carbonyl compounds.
- Precursor for Specialty Chemicals: It is employed in the laboratory and in specialized industrial processes for the synthesis of certain pharmaceuticals, agrochemicals, and dyes where a brominated carbonyl moiety is specifically required.
- Historical Context: Like its chlorine analog, phosgene, carbonyl bromide was investigated for its potential as a chemical warfare agent during the early 20th century. While it exhibits strong lachrymatory (tear-gas) properties and is highly toxic, its higher instability and lower efficacy compared to phosgene meant it was not widely adopted for this purpose.
Safety and Handling
Carbonyl bromide is an extremely hazardous substance that requires stringent safety protocols for handling and storage.
- Toxicity: It is highly toxic by inhalation, ingestion, and skin absorption. Exposure to its vapors can cause severe irritation to the respiratory tract, leading to pulmonary edema, chemical pneumonitis, and potentially fatal lung damage.
- Corrosivity and Lachrymator: It is corrosive to the skin, eyes, and mucous membranes, causing severe burns and irritation upon contact. It is also a potent lachrymator, inducing intense tearing, eye pain, and temporary blindness even at low concentrations.
- Handling Precautions: Due to its high toxicity and reactivity, carbonyl bromide must be handled exclusively in a well-ventilated fume hood or an inert atmosphere glove box. Full personal protective equipment, including a self-contained breathing apparatus (SCBA) or airline respirator, chemical-resistant gloves, and eye protection (face shield and safety goggles), is essential.
- Storage: It should be stored in tightly sealed, chemically resistant containers in a cool, dry, and well-ventilated area, away from moisture, strong bases, and other incompatible materials that could promote its decomposition or reaction.