carboxylic acid & 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
• Carboxylic acids dissolve in water because they can hydrogen bond to water molecules
• Acidity of carboxylic acids

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

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


  • Stabilised by delocalisation
  • Delocalisation makes dissociation more likely
• Delocalisation in carboxylic acid salts results in equal C-O bond lengths
• Increasing chain length of carboxylic acids

  Pushes electron density onto the COO- ion, making it more negative and less stable, decreasing acid strength
• Electron withdrawing groups on carboxylic acids

  Withdraw electron density from the COO- ion, making it less negative and more stable, increasing acid strength
• Carboxylic acids


  • Propanoic acid
  • Chloroethanoic acid
• Esterification


  Reaction of carboxylic acids with alcohols, in the presence of an acid catalyst, to form esters and water
• Ester naming

  Two parts - the bit ending in -yl comes from the alcohol, the bit ending in -anoate comes from the carboxylic acid
• Esterification reaction is reversible, slow, and gives low yields
• Uses of esters


  • Pleasant smells
  • Used as solvents for polar organic substances
  • Used as plasticisers for polymers
• Esters have lower boiling points than the carboxylic acids they are derived from
• Oxidation of methanoic acid

  Methanoic acid can be oxidised to form 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
• Effervescence with carbonates/bicarbonates can be used as a functional group test for carboxylic acids
• Hydrolysis of esters with acid

  Ester + water ⇌ carboxylic acid + alcohol
• Hydrolysis of esters with sodium hydroxide

  Ester + NaOH → carboxylic acid salt + alcohol
• Hydrolysis with NaOH goes to completion, hydrolysis with acid is reversible
• 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, used in cosmetics, food, and glues
• Conversion of vegetable oils to biodiesel

  Vegetable oil + methanol (with alkali catalyst) → biodiesel (mixture of methyl esters of long chain carboxylic acids) + glycerol
• Biodiesel can be considered carbon-neutral as the CO2 released on burning was previously absorbed by the plants
• Hydrophobic

  Mixes with grease
• Glycerol (propane-1,2,3-triol)


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

  Reaction with methanol in presence of strong alkali catalyst
• Biodiesel


  Mixture of methyl esters of long chain carboxylic acids
• Biodiesel produced from this method can be classed as carbon-neutral as carbon dioxide given off when burnt would have been extracted from air by photosynthesis when plant grew
• If energy for processes like irrigating plants, extracting oil, heating reaction comes from fossil fuels then biodiesel is not carbon neutral
• Biodiesel production can affect land available for food production
• Acyl chlorides


  Much more reactive than carboxylic acids
• Acid anhydrides


  Similar reactivity to acyl chlorides, bring about same changes in functional groups
• Cl and -OCOCH3 groups

  Good leaving groups, make acyl chlorides and acid anhydrides more reactive than carboxylic acids and esters
• Reaction of acyl chloride with water


  Acyl chloride converted to carboxylic acid, HCl gas given off
• Reaction of acid anhydride with water

  Acid anhydride converted to two carboxylic acids
• Reaction of acyl chloride with alcohol

  Acyl chloride converted to ester, HCl gas given off