Carboxylic acids and derivatives

• Carboxylic acids


  Organic compounds containing the carboxyl group (-COOH)
• Solubility of carboxylic acids in water

  • Smaller carboxylic acids (up to C4) dissolve in water in all proportions
  • Solubility rapidly reduces after C4 due to reduced ability to hydrogen bond with water
• Acidity of carboxylic acids

  • Carboxylic acids are weak acids that only slightly dissociate in water
  • But they are strong enough to displace carbon dioxide from carbonates
• Dissociation of carboxylic acids

  CH3CO2H(aq) ⇌ CH3CO2-(aq) + H+(aq)
• Carboxylic acid salts


  • Stabilized by delocalisation
  • Equal C-O bond lengths in delocalised ion
  • Delocalisation makes dissociation more likely
• Increasing chain length of carboxylic acids

  • Pushes electron density onto COO- ion, making it more negative and less stable
  • This makes the acid less strong
• Electronegative substituents on carboxylic acids

  • Withdraw electron density from COO- ion, making it less negative and more stable
  • This makes the acid more strong
• Propanoic acid vs Ethanoic acid

  Propanoic acid is less acidic than Ethanoic acid
• Chloroethanoic acid vs Ethanoic acid

  Chloroethanoic acid is more acidic than Ethanoic acid
• Naming carboxylic acids


  End in -oic acid, no number needed for acid group as it's always at the end
• Dioic acids


  Carboxylic acid groups on both ends of the chain
• Esterification


  1. Carboxylic acid + Alcohol ⇌ Ester + Water

  2. Reaction is reversible, slow, needs heating and acid catalyst
• Ester naming


  Two parts - alcohol part ending in -yl, acid part ending in -anoate
• Uses of esters


  • Perfumes and flavourings
  • Solvents
  • Plasticizers for polymers
• Oxidation of methanoic acid

  Methanoic acid can be oxidized to carbonic acid (H2CO3) which decomposes to CO2
• Salt formation reactions of carboxylic acids

  1. Acid + Metal → Salt + Hydrogen

  2. Acid + Alkali → Salt + Water

  3. Acid + Carbonate → Salt + Water + CO2
• Hydrolysis of esters


  1. With acid: Ester + Water ⇌ Carboxylic acid + Alcohol

  2. With base: Ester + NaOH → Carboxylic acid salt + Alcohol
• Fats and oils


  • Esters of glycerol and long chain carboxylic (fatty) acids
• Hydrolysis of fats and oils

  Fats/oils + KOH → Soap + Glycerol + Long chain carboxylic (fatty) acids
• Soap


  Long chain carboxylic (fatty) acids that act as soaps - polar CO2- end is hydrophilic, non-polar hydrocarbon chain is hydrophobic
• Glycerol


  Readily soluble in water due to ability to form hydrogen bonds
• Conversion of vegetable oils to biodiesel

  Vegetable oil + Methanol → Biodiesel (mixture of methyl esters of long chain carboxylic acids) + Glycerol
• Glycerol (propane-1,2,3-triol)


  Forms hydrogen bonds very easily and is readily soluble in water. Used in cosmetics, food and in glues.
• Vegetable oils can be converted into biodiesel


  Reaction with methanol in the presence of a (strong alkali) catalyst
• Biodiesel


  A mixture of methyl esters of long chain carboxylic acids
• The biodiesel produced from this method can be classed as carbon–neutral as any carbon dioxide given off when the biofuel is burnt would have been extracted from the air by photosynthesis when the plant grew.
• This does not take into account any energy needed to irrigate plants, extract the oil, heat the reaction with methanol mixture or process the fuel. If the energy for these processes comes from fossil fuels then the biofuel produced is not carbon neutral.
• It also does not take into account the effect on land available for food production.
• Acyl chlorides


  Much more reactive than carboxylic acids
• Acid anhydrides


  Have a similar reactivity to acyl chlorides and therefore bring about the same changes in functional groups
• Acyl chlorides and acid anhydrides

  • The Cl and –OCOCH3 groups are classed as good leaving groups (to do with less effective delocalisation.) This makes acyl chlorides and acid anhydrides much more reactive than carboxylic acids and esters
• Reaction of acyl chloride with water

  Acyl chloride carboxylic acid
• Reaction of acid anhydride with water

  Acid anhydride carboxylic acid
• Reaction of acyl chloride with alcohol

  Acyl chloride ester
• Reaction of acid anhydride with alcohol

  Acid anhydride ester
• Reaction of acyl chloride with ammonia

  Acyl chloride primary amide
• Reaction of acid anhydride with ammonia

  Acid anhydride primary amide
• Reaction of acyl chloride with primary amine

  Acyl chloride secondary amide
• Reaction of acid anhydride with primary amine

  Acid anhydride secondary amide
• Recrystallisation


  • An appropriate solvent is one which will dissolve both compound and impurities when hot and one in which the compound itself does not dissolve well when cold. The minimum volume is used to obtain a saturated solution and to enable crystallisation on cooling.