Carboxylic acids and Esters

• A carboxylic acid is a molecule with an alcohol group (-OH) bonded to a carbonyl group (C=O) to form a carboxyl group (-COOH)
• Carbonate is used to test for carboxylic acids as it forms carbon dioxide when reacted which produces bubbles/effervescence
• Carboxylic acids use the suffix -enoic acid if a double bond is present
• Carboxylic acids are soluble in water because they can form hydrogen bonds with water molecules
• Two carboxylic acid molecules can form a dimer by hydrogen bonding. This gives carboxylic acids high melting points
• Carboxylic acid + metal --> salt + hydrogen

  HCOOH + Na --> HCOONa + H2
• Carboxylic acid + metal oxide --> salt + water
• Carboxylic acid + metal hydroxide --> salt + water
• Carboxylic acid + metal carbonate --> salt + water + carbon dioxide
• Carboxylic acids ionise to form a H+ ion and a carboxylate ion. These use the -oate suffix

  Ethanoic acid --> Ethanoate ion

  Propanoic acid --> Propanoate ion
• Carboxylic acids act as acids when they lose a H+ ion in a reaction. Forms negatively charged carboxylate ion.

  Only occurs because of the carboxyl group
• In a carboxylate ion, the extra electron is delocalised over 3 atoms, making the ion more stable
• Esters are molecules that contain the ester functional group R-COOR' where R' begins with a carbon atom

  
• Carboxylic acid + alcohol --> ester + water

  ethanoic acid + propan-1-ol --> propyl ethanoate + water
• Esterification occurs when a carboxylic acid reacts with an alcohol under reflux (heat needed) in the presence of an acid catalyst such as sulfuric acid
• Naming esters

  alcohol-yl carboxylate

  e.g methanol + ethanoic acid --> methyl ethanoate
• 3-methylbutyl propanoate

  
• Uses of esters

  • food flavouring
  • perfumes
  • solvents
  • plasticisers
• Hydrolysis

  ester + water --> alcohol and carboxylic acid

  conditions: acid catalyst

  reversable
• Hydrolysis under alkaline conditions

  ester + alkali --> salt + alcohol

  non reversible
• Glycerol - propane-1,2,3-triol

  forms hydrogen bonds very easily

  
• Uses of glycerol

  • solvent
  • plasticiser
  • moisturising agent
• carboxylic acid + glycerol --> ester

  these esters are commonly found in animal fats and vegetable oil
• ester + alkali --> salt + alcohol

  you can hydrolyse long chain esters in alkaline conditions to form a soap. This is known as saponification.
• Methyl esters are the best fuels
• Biodiesel - mixture of long chain methyl esters

  formed by reacting vegetable oil with methanol

  Long chain ester + methanol --> glycerol + methyl ester

  strong alkaline catalyst