6.7 carboxylic acids and derivatives

Question 1

why are carboxylic acids more acidic than phenols?

Answer 1

RCOO- conjugate base is stabilised by the delocalisation of negative charge over two highly electronegative oxygen atoms. this decreases the charge density of negative charge on O atom and stabilises the anion

Question 2

what are the methods of preparation of carboxylic acids (4 mechanisms)?

Answer 2

1. strong oxidation of alkenes (KMnO4 in H2SO4, heat under reflux)
2. oxidation of arenes to benzoic acid (KMnO4 in H2SO4, heat under reflux)
3. oxidation of primary alcohols and aldehydes (KMnO4 / K2Cr2O7 in H2SO4, heat under reflux)
4. acidic or basic hydrolysis of nitriles (HCl/H2SO4, heat under reflux OR NaOH/KOH, heat under reflux)

Question 3

what are the reactions of carboxylic acids (5 mechanisms)?

Answer 3

1. reduction to primary alcohols (LiAlH4 in dry ether)
2. redox / acid metal displacement (Na)
3. neutralisation (Na2CO3 OR NaOH)
4. condensation with alcohols to esters (conc. H2SO4)
5. nucleophilic substitution (PCl3, heat OR PCl5(s) OR SOCl2 in pyridine, heat)

Question 4

what are the chemical tests, observations and type of reactions for carboxylic acids (2)?

Answer 4

1. PCl5 (s)
   - white fumes of HCl observed, nucleophilic substitution
2. Na2CO3
   - effervescence of gas which forms white ppt in calcium hydroxide, neutralisation

Question 5

what are the reactions of acyl chlorides (2 mechanisms)?

Answer 5

1. hydrolysis to carboxylic (H2O)
2. condensation with alcohol / phenol + NaOH / carboxylic acid / ammonia / amine

Question 6

what are the reactions of esters (2)?

Answer 6

1. acidic hydrolysis to carboxylic acid and alcohols (HCl/H2SO4, heat under reflux)
2. basic hydrolysis to carboxylate salt and alcohols (NaOH/KOH, heat under reflux)