Chlorination with thionyl chloride

Overview

Thionyl chloride converts carboxylic acids into acyl chlorides with sulfur dioxide and hydrogen chloride as by-products.

Transformation

Carboxylic acids → Acyl chlorides

Equation

R-CO2H + SOCl2 -> R-COCl + SO2 + HCl

Reagents

SOCl2

Environment

mild conditions

Reaction class

substitution

Mechanism

acyl chloride formation

Evidence level

textbook extension

Scope and limitations

Scope

Carboxylic acids can be converted into acyl chlorides using thionyl chloride.

Limitations

This is a reagent variant of acyl chloride formation; it is kept separate from the PCl5 route and does not imply the same displayed mechanism.

Related reactions

• Oxidation: Alcohols → Carboxylic acids

  Full oxidation of a primary alcohol gives a carboxylic acid.

• Complete oxidation: Primary alcohols → Carboxylic acids

  Full oxidation of a primary alcohol gives a carboxylic acid.

• Reduction: Carboxylic acids → Primary alcohols

  Reduction of a carboxylic acid gives a primary alcohol.

• Oxidation: Aldehydes → Carboxylic acids

  Oxidation of an aldehyde gives a carboxylic acid.

• Hydrolysis: Nitriles → Carboxylic acids

  Nitriles can be hydrolysed to carboxylic acids, splitting the old aggregate nitrile-to-amide route into a single functional-group conversion.

• Activation for amide formation: Carboxylic acids → Amide chemistry

  Carboxylic acids or activated acid derivatives connect to amide-bond formation.

• Esterification: Carboxylic acids → Esters

  Carboxylic acids react with alcohols to form esters.

• Hydrolysis: Esters → Carboxylic acids

  Hydrolysis converts esters back into carboxylic acid products.

• Chlorination: Carboxylic acids → Acyl chlorides

  PCl5 converts carboxylic acids into acyl chlorides.

• Hydrolysis: Acyl chlorides → Carboxylic acids

  Water hydrolyses acyl chlorides to carboxylic acids, releasing hydrogen chloride.

• Acylation: Acyl chlorides → Esters

  Alcohol acylation converts acyl chlorides into esters.

• Acylation: Acyl chlorides → Amides

  Ammonia acylation converts acyl chlorides into amides.

• Acylation: Acyl chlorides → N-substituted amides

  Amine acylation converts acyl chlorides into N-substituted amides.

• Carboxylation: Grignard reagents → Carboxylic acids

  Grignard carboxylation gives carboxylic acids after acidic work-up.

• Grignard carboxylation co reactant: Carbon dioxide → Carboxylic acids

  Carbon dioxide plus a Grignard reagent gives a carboxylic acid after acidic work-up.

• Salt formation: Carboxylic acids → Carboxylate salts

  Carboxylic acids react with bases, carbonates and reactive metals to form carboxylate salts.

References

1. Organic Chemistry: Chemistry of Acid HalidesJohn McMurry · OpenStax Organic Chemistry · 2023

   Supports acid-halide preparation with thionyl chloride and nucleophilic acyl substitution chemistry, including tetrahedral intermediates, hydrolysis, alcoholysis and amine acylation at acid chlorides.