Carboxylic Acids and Esters

• carboxylic acids are produced by oxidation of primary alcohols under reflux
• Carboxylic acids dissolve in polar solvents like water as they hydrogen bond with water molecules

  ->The hydrocarbon part doesn't hydrogen bond therefore the longer the hydrocarbon chain, the less soluble the carboxylic acid
• Carboxylic acids are weak acids as only partially dissociate in water to form a carboxylate anion.

  • equilibrium lies to the left hand side as it dissociates poorly
  • anion is stable due to delocalisation (like in benzene)
• Oxidation of Carboxylic acids only occurs in methanoic acid
• acid + metal -> salt + hydrogen
• acid + alkali -> salt + water
• Acid + carbonate -> salt + carbon dioxide + water
• what is the test for acids?

  Carbonate to produce carbon dioxide (bubble through limewater)
• esterfication:

  Carboxylic acids + alcohol -> ester + water

  • catalyst: concentrated H2SO4
  • condensation reaction as produces a small molecule
• Esters are insoluble and have low boiling points (can't H bond like Carboxylic acids)
• hydrolysis- converts esters to alcohols and carboxylic acids by adding water. Two types: Acid catalysed and Base
• Acid catalysed hydroysis:

  ester + water -> carboxylic acid + alcohol

  • dilute H2SO4 catalyst
  • heated under reflux
  • reversible reaction so poor yield- less favourable hydrolysis
• Base hydrolysis (saponification):

  ester + base -> carbonate salt + alcohol

  carbonate salt + acid -> carboxylic acid

  • salts are used as soaps as have hydrophilic (polar head) and hydrophobic (non-polar chain) properties.
• Carbon neutral:

  1. photosynthesis: 6 CO2 + 6 H2O -> C6H12O6 + 6 O2
  2. anaerobic respiration: C6H12O6 -> 2 CH3CH2OH + 2 CO2
  3. combustion: 2 CH3CH2OH + 6 O2 -> 4 CO2 + 6 H2O

  • 6 Co2 molecules on each side therefore carbon neutral
  • doesn't include: energy use or transport of materials
• Triglycerides are lipids and can be either vegetable oils or animal fats.

  • veg oil: unsaturated, weak IMF as chains not close together therefore liquid at room temp
  • animal fats: saturated, strong IMF as chains close together therefore solid at room temp
• Triglyceride ester:

  glycerol + fatty acid -> triglyceride
• Glycerol (propane-1,2,3-triol) is soluble as forms H bonds and is used in cosmetics, food and glue.
• Biodiesel ( base catalysed trans esterification)

  triglyceride + methanol -> glycerol + methyl ester (BIODIESEL)

  • with NaOH catalyst