3.3.9 carboxylic acids

• Ethanoic acid vs Ethanedioic acid

  In the ion formed from ethanoic acid, the CH3 group pushes electron density via the inductive effect towards the COO- group

  > Making the ion less stable.

  > Therefore the ion will more readily combine with the H+ ion

  > So fewer H+ ions are formed

  > So, ethanoic acid is a weaker acid
• Ethanoic acid vs Ethanedioic acid

  In the ion produced from ethanedioic acid, the COOH group contains electronegative oxygen atoms

  > Which pulls electron density away from the COOH- group

  > Making the ion more stable

  > Therefore the ion is less likely to combine with H+ ion

  > So there are more H+ ions

  > Making ethanedioic acid a stronger acid than ethanoic acid
• Ester Hydrolysis:

  Carboxylic acids + Alcohol ⇌ Ester + Water

  Catalyst: Conc H2SO4
• Acid - Catalysed Hydrolysis:

  Ester + Water ⇌ Alcohol + Carboxylic Acid

  Reagent/Conditions: Reflux - dilute aqueous sulfuric acid
• Base - catalysed hydrolysis:

  Ester + Sodium Hydroxide ⇌ Alcohol + Carboxylate salt

  Reagent/Conditions: Reflux - dilute NaOH
• Propane-1,2,3-triol(glycerol) + fatty acid(COOH)->Triglyceride + 3H20
• Glycerol is used in cosmetics and food.

  The long chain carboxylate salts are used in the manufacture of soap.
• Biodiesel is made by heating vegetable oils (Ester) with methanol and NaOH.

  This produces propane-1,2,3-triol (glycerol)and methyl esters

  Methyl esters are used to make biodiesel
• Acid anhydrides are preferred over acyl chlorides:

  > Acyl chlorides produce corrosive fumes of HCl.

  > Acyl chlorides are vulnerable to hydrolysis

  > Acid anhydrides are cheaper, less violent reactions and easier to store
• Esters are used in solvents plasticisers, perfumes and food flavourings
• Why is KOH used when hydrolysing esters. To make sure the reactants are miscible.
• Nucleophilic add-elim -Acid anhydride/ Acyl chloride

  Conditions: for acid anhydride warm

  Reagents: Water, Alcohol, Ammonia, 1° Amine

  Forms: Carboxylic acid, Ester, Amide, N-substituted amide
• Biodiesel - is made from vegetable oils and animal fats.

  A) Vegetable oil

  B) methanol

  C) Propane-1,2,3-triol

  D) Biodiesel