Free radical bromination
Photochemical bromination can convert alkanes into bromoalkanes.
- Reagents
- Br2
- Conditions
- hν
- Reaction class
- radical substitution
- Equation
- R-H + Br2 -> R-Br + HBr
Overview
Photochemical bromination can convert alkanes into bromoalkanes.
Transformation
- Equation
- R-H + Br2 -> R-Br + HBr
- Reagents
- Br2
- Environment
- hν
- Reaction class
- radical substitution
- Mechanism
- free-radical substitution
- Evidence level
- textbook core
Scope and limitations
- Scope
- Alkanes can be brominated under photochemical conditions to form bromoalkanes.
- Limitations
- This Br2/UV bromoalkane branch uses ethane mono-bromination as the mechanism exemplar. Longer or branched alkanes can still give positional isomer mixtures and termination by-products; this route does not generalize a full downstream bromoalkane route family.
Related reactions
- Bromination: Alcohols → Bromoalkanes
Bromide and acid conditions convert alcohols into bromoalkanes.
- Hydrobromination: Alkenes → Bromoalkanes
Addition of hydrogen bromide across an alkene can form a bromoalkane.
- Cyanation: Bromoalkanes → Nitriles
Cyanide substitution forms a nitrile and extends the carbon chain by one carbon.
- Amination: Bromoalkanes → Amines
Ammonia substitutes bromide to form a primary amine; excess ammonia limits further alkylation.
- Hydrolysis: Bromoalkanes → Alcohols
The C-Br bond can be displaced by hydroxide to form an alcohol.
- Elimination: Bromoalkanes → Alkenes
Base-promoted elimination removes HBr to form an alkene.
- Free radical chlorination: Alkanes → Chloroalkanes
Photochemical chlorination can convert alkanes into chloroalkanes.
- Cracking: Alkanes → Alkenes
Thermal or catalytic cracking converts long-chain alkanes into shorter molecules including alkenes.
- Hydrogenation: Alkenes → Alkanes
Hydrogenation reduces alkenes to alkanes.
- Grignard formation: Bromoalkanes → Grignard reagents
Bromoalkanes can react with magnesium in dry ether to form Grignard reagents.
- Complete combustion: Alkanes → Carbon dioxide
Alkanes burn completely in excess oxygen to form carbon dioxide and water.
References
- Organic Chemistry: Preparing Alkyl Halides from Alkanes: Radical HalogenationJohn McMurry · OpenStax Organic Chemistry · 2023
Supports alkane reaction with Cl2 under ultraviolet light to form chloroalkanes by radical halogenation, including initiation, propagation, termination, product mixtures and multiple chlorination; analogous bromination is retained as a scope boundary.