Free radical chlorination
Photochemical chlorination can convert alkanes into chloroalkanes.
- Reagents
- Cl2
- Conditions
- hν
- Reaction class
- radical substitution
- Equation
- R-H + Cl2 -> R-Cl + HCl
Overview
Photochemical chlorination can convert alkanes into chloroalkanes.
Transformation
- Equation
- R-H + Cl2 -> R-Cl + HCl
- Reagents
- Cl2
- Environment
- hν
- Reaction class
- radical substitution
- Mechanism
- free-radical substitution
- Evidence level
- textbook core
Scope and limitations
- Scope
- Alkanes can be chlorinated under photochemical conditions to form chloroalkanes.
- Limitations
- The mechanism diagram uses ethane mono-chlorination as the exemplar, not a selective synthesis claim. Longer or branched alkanes can give positional isomer mixtures, further chlorination/overchlorination products, and termination by-products; bromination would give bromoalkanes and is not recorded as this chloroalkane route.
Related reactions
- Chlorination: Alcohols → Chloroalkanes
Alcohols can be converted into chloroalkanes to create a better leaving group for downstream substitution.
- Chlorination with thionyl chloride: Alcohols → Chloroalkanes
Thionyl chloride converts alcohols into chloroalkanes with sulfur dioxide and hydrogen chloride as by-products.
- Hydrochlorination: Alkenes → Chloroalkanes
Addition of hydrogen chloride across an alkene can form a chloroalkane.
- Hydrolysis: Chloroalkanes → Alcohols
The C-Cl bond can be displaced by hydroxide to form an alcohol.
- Cyanation: Chloroalkanes → Nitriles
Cyanide substitution forms a nitrile and extends the carbon chain by one carbon.
- Amination: Chloroalkanes → Amines
Ammonia substitutes chloride to form a primary amine; excess ammonia limits further alkylation.
- Elimination: Chloroalkanes → Alkenes
Base-promoted elimination removes HCl to form an alkene.
- Free radical bromination: Alkanes → Bromoalkanes
Photochemical bromination can convert alkanes into bromoalkanes.
- 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: Chloroalkanes → Grignard reagents
Chloroalkanes 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.