Carboxyl

Question 1

Preparation

Answer 1

1.From alkenes: Vigorous oxidation
Oxidation of terminal alkenes attached to one H and one R
H2SO4 (aq) and KMnO4(aq) heat
2.From Aldehyde: Oxidation
H2SO4(aq) and KMnO4/K2Cr2O7 heat
3.From primary alcohol: Oxidation
H2SO4(aq) and KMnO4/K2Cr2O7 heat w reflux
4.From esters: Acidic hydrolysis also forms alcohol
HCl(aq), heat
5.From amides acidic hydrolysis also forms amine
HCl(aq), heat
6.From acyl chlorides: Hydrolysis
H2O(l), r.t.
7.From alkyl benzene side chain oxidation
H2SO4(aq), KMnO4 (aq), heat
8.Nitrile acidic hydrolysis
HCl(aq), heat

Question 2

Why carboxylic acids are the most acidic compared to phenols and alkoxide?

Answer 2

Carboxylic acids have a double resonance structure due to the delocalisation of negative charge over two highly negative O atoms. This greatly stabilises the carboxylate anion. Hence acid dissociation is most favoured

Question 3

Physical properties

Answer 3

Polar and soluble in water as it can form H bonds with water mol.
Solubility in water decreases as hydrocarbon chain lengthens
MP and BP depends on size of electron cloud, degree of branching and extensiveness of H bonding (2 per mol, usually)

Question 4

Reactions

Answer 4

1. Redox
   Na(s) to form carboxylate Na+
2. Acid base w SB
   Carboxylate Na+ salt and water
   NaOH(aq)
3. Acid base with WB
   NH3(g)
   Carboxylate salt which is the conjugate acid of the WB
4. Acid base with Na2CO3
   Carboxylate Na+ salt and CO2 (effervescence) and water
5. Condensation to form ester
   H2SO4 conc, R-OH, heat
6. Substitution to form acyl chlorides
   PCl3 anhydrous
   PCl5 anhydrous
   SOCl2 anhydrous
   HX(g) dry

Question 5

Acyl chlorides
Preparation

Answer 5

1. Substitution of CA

Question 6

Acyl chloride reaction

Answer 6

1. Hydrolysis with water to form CA
   - H2O(l)
2. Alkaline hydrolysis to form carboxylate salt
   - NaOH(aq)
3. Condensation to form ester
   - ROH
4. Condensation to form primary, tertiary and secondary amides
   - NH3(g) to form -CONH2R
   - RNH2 to form -CONHRR
   - RNHR to form -CONRRR

Question 7

Esters
Reaction

Answer 7

1. Acidic hydrolysis
   HCl(aq) heat to form COOH and OH

2.Alkaline hydrolysis
NaOH(aq) heat to form COO- and OH

Question 8

Acyl chloride are have the most ease of hydrolysis followed by alkyl chloride then chloro benzene why?

Answer 8

• Electronic factor: This is because C in acyl chlorides bonded to one highly electronegative O and Cl electron withdrawing groups inducing a greater partial positive charge on C which makes C much more electron deficient than in the other chlorides. Thus most susceptible to nucleophilic attack by an electron rich species
• Steric hindrance is lesser due to lesser R groups being present making it easier for nucleophile to attack the electron deficient