Chlorination with thionyl chloride

Overview

Thionyl chloride converts alcohols into chloroalkanes with sulfur dioxide and hydrogen chloride as by-products.

Transformation

Alcohols → Chloroalkanes

Equation

R-OH + SOCl2 -> R-Cl + SO2 + HCl

Reagents

SOCl2

Environment

mild conditions

Reaction class

halogenation

Mechanism

halogenation

Evidence level

textbook extension

Scope and limitations

Scope

Primary and secondary alcohols can be converted into chloroalkanes using thionyl chloride.

Limitations

This is an advanced reagent variant of alcohol chlorination; it is kept separate from the PCl5 route and does not imply the same displayed mechanism.

Related reactions

• Chlorination: Alcohols → Chloroalkanes

  Alcohols can be converted into chloroalkanes to create a better leaving group for downstream substitution.

• Bromination: Alcohols → Bromoalkanes

  Bromide and acid conditions convert alcohols into bromoalkanes.

• Iodination: Alcohols → Iodoalkanes

  Iodine and red phosphorus conditions convert alcohols into iodoalkanes.

• 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.

• Hydrolysis: Bromoalkanes → Alcohols

  The C-Br bond can be displaced by hydroxide to form an alcohol.

• Hydrolysis: Iodoalkanes → Alcohols

  The C-I bond can be displaced by hydroxide to form an alcohol.

• Oxidation: Alcohols → Aldehydes

  Controlled oxidation of a primary alcohol gives an aldehyde.

• Oxidation: Alcohols → Ketones

  Oxidation of a secondary alcohol gives a ketone.

• Oxidation: Alcohols → Carboxylic acids

  Full oxidation of a primary alcohol gives a carboxylic acid.

• Free radical chlorination: Alkanes → Chloroalkanes

  Photochemical chlorination can convert alkanes into chloroalkanes.

• Hydration: Alkenes → Alcohols

  Catalytic hydration converts alkenes into alcohols.

• Dehydration: Alcohols → Alkenes

  Dehydration converts alcohols into alkenes.

References

1. Organic Chemistry: Preparing Alkyl Halides from AlcoholsJohn McMurry · OpenStax Organic Chemistry · 2023

   Supports primary and secondary alcohol conversion to alkyl chlorides with thionyl chloride under mild conditions, with reduced acid-catalysed rearrangement risk compared with HX methods.