6.1.3 CARBOXYLIC ACIDS & ESTERS

• • Carboxyl functional group, -COOH
  • General formula CnH2n+1COOH(RCOOH)
  • Nomenclature = alkan + oic acid, e.g. propanoic acid
• • Carboxylic acids with fewer than six carbon atoms per molecule are water-soluble
  • Can hydrogen-bond with the functional group
  • In aqueous solution they are only slightly ionised, to give low concentrations of hydrogen ions and carboxylate (COO-) ions

  They do not fully dissociate in water, the position of the equilibrium lies to the left

  • This partial ionisation in solution means that carboxylic acids are weak acids
• Carboxylic Acids

  • Can form salts with metals, alkalis and carbonates.
  • +metal oxides → a metal salt + water
  • e.g. + magnesium → magnesium ethanoate (salt) + water

  2CH3COOH (aq) + MgO (s) → (CH3COO)2Mg (aq) + H2O (l)

  • +alkali → salt + water
  • Neutralisation reaction
  • e.g. +potassium hydroxide → potassium ethanoate (salt) + water

  CH3COOH (aq) + KOH (aq) → CH3COOK (aq) + H2O (l)

  • +carbonate → metal salt + water + carbon dioxide gas
  • e.g. +potassium carbonate → potassium ethanoate (salt) + water+ carbon dioxide

  2CH3COOH (aq) + K2CO3 (s) → 2CH3COOK (aq) + H2O (l) + CO2 (g)
• Esterification of Carboxylic Acids & Acid Anhydrides

  • Ester group, -COO-
  • An ester is named after the parent carboxylic acid from which it is derived
  • Nomenclature of esters:
  • Remove the -oic acid suffix from the parent carboxylic acid and replace with oate
  • Add the alkyl chain attached to the oxygen atom of the -COO- group as the first word in the name
• • Esters = sweet and fruity smell
  • Condensation reaction/esterification between a carboxylic acid and alcohol with concentrated H2SO4 as catalyst, eliminating water
  • Involves the elimination of a small molecule not always water
  • Reversible reaction
  • Slow reaction- needs heating under reflux
  • Low yields(~50%) tend to be achieved by this route

  Esters are formed from the condensation reaction between carboxylic acids and alcohols
• What process can occur by reacting acid anhydrides with alcohols at room temperature?

  Esterification
• What are acid anhydrides derived from?

  • Derivatives of carboxylic acids
  • Formed by substitution of the -OH group by an alkanoate (e.g., ethanoate, propanoate)
• How is the nomenclature of acid anhydrides determined?

  Identify the parent hydrocarbon chain and add the suffix -oic anhydride
• What is another method for naming acid anhydrides?

  Remove the -oic acid from the carboxylic acid and add -oic anhydride
• How do acid anhydrides compare in reactivity to carboxylic acids?

  • Acid anhydrides are more reactive than carboxylic acids
• What is a key characteristic of the esterification reaction involving acid anhydrides?

  It is not reversible and achieves a higher yield
• What is produced during the hydrolysis of esters?


  Carboxylic acid and alcohol
• What conditions are required for the hydrolysis of esters using dilute acid?

  Heating under reflux with dilute acid
• How does the hydrolysis of esters by dilute acid differ from that by dilute alkali?

  The hydrolysis by dilute acid is reversible, while that by dilute alkali is irreversible
• What type of acid is commonly used in the hydrolysis of esters?

  Dilute sulfuric acid
• What is the result of heating an ester under reflux with dilute alkali?

  It forms a sodium carboxylate salt and alcohol
• What must happen to the sodium carboxylate salt to convert it into a carboxylic acid?

  It needs to be protonated by an acid
• What is the role of HCl in the hydrolysis of esters by dilute alkali?

  To protonate the sodium carboxylate ion
• What are the key differences between ester hydrolysis by dilute acid and dilute alkali?

  • Hydrolysis by dilute acid:
  • Reversible reaction
  • Produces carboxylic acid and alcohol
  • Hydrolysis by dilute alkali:
  • Irreversible reaction
  • Produces sodium carboxylate salt and alcohol
• What is the functional group present in acyl chlorides?


  • COCl
• Why are acyl chlorides more useful than carboxylic acids in organic reactions?

  They are more reactive than carboxylic acids.
• What is the reaction that produces acyl chlorides from carboxylic acids?

  Carboxylic acids react with liquid sulfur dichloride oxide (SOCl2).
• What is the product of the reaction between propanoic acid and SOCl2?

  Propanoyl chloride, SO2, and HCl.
• What are the main uses of acyl chlorides?

  • Addition-elimination reactions
  • Hydrolysis to form carboxylic acids
  • Reaction with alcohols and phenols to form esters
  • Reaction with ammonia and amines to form amides
• What type of reaction occurs during the hydrolysis of acyl chlorides?

  It is an addition-elimination reaction.
• What are the products of the hydrolysis of acyl chlorides?

  Carboxylic acid and HCl.
• What happens to a water molecule during the hydrolysis of acyl chlorides?

  A water molecule adds across the C=O bond.
• What is formed when acyl chlorides react with alcohols and phenols?

  Esters.
• What is required for the reaction of acyl chlorides with phenols?

  Heat and a base.
• What type of reaction occurs when acyl chlorides form esters?

  It is an addition-elimination reaction.
• What is the product when acyl chlorides react with ammonia and amines?

  Amides.
• How do amines and ammonia react with acyl chlorides to form amides?

  The nitrogen atom attacks the carbonyl carbon atom in the acyl chlorides.
• What type of amide is formed when acyl chlorides react with ammonia?

  Primary amide.
• What type of amide is formed when acyl chlorides react with primary amines?

  Secondary amide.
• What happens during the addition-elimination reaction of acyl chlorides with amines?

  The amine or ammonia molecule adds across the C=O bond, and HCl is eliminated.
• What are the key steps in the formation of amides from acyl chlorides?

  1. Acyl chloride reacts with ammonia or amines.
  2. Nitrogen atom attacks the carbonyl carbon.
  3. Addition-elimination reaction occurs.
  4. Primary or secondary amide is formed.
• Dilute sulfuric acid


  A mild and gentle acid commonly used in the hydrolysis reaction to break down esters into their acid and alcohol components.
• Hydrochloric acid


  A strong acidic solution that should be avoided in the hydrolysis reaction due to its potential to break down the ester too quickly or react with it in unwanted ways.