Carboxyl Flashcards
Preparation
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
Why carboxylic acids are the most acidic compared to phenols and alkoxide?
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
Physical properties
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)
Reactions
- Redox
Na(s) to form carboxylate Na+ - Acid base w SB
Carboxylate Na+ salt and water
NaOH(aq) - Acid base with WB
NH3(g)
Carboxylate salt which is the conjugate acid of the WB - Acid base with Na2CO3
Carboxylate Na+ salt and CO2 (effervescence) and water - Condensation to form ester
H2SO4 conc, R-OH, heat - Substitution to form acyl chlorides
PCl3 anhydrous
PCl5 anhydrous
SOCl2 anhydrous
HX(g) dry
Acyl chlorides
Preparation
- Substitution of CA
Acyl chloride reaction
- Hydrolysis with water to form CA
- H2O(l) - Alkaline hydrolysis to form carboxylate salt
- NaOH(aq) - Condensation to form ester
- ROH - Condensation to form primary, tertiary and secondary amides
- NH3(g) to form -CONH2R
- RNH2 to form -CONHRR
- RNHR to form -CONRRR
Esters
Reaction
- Acidic hydrolysis
HCl(aq) heat to form COOH and OH
2.Alkaline hydrolysis
NaOH(aq) heat to form COO- and OH
Acyl chloride are have the most ease of hydrolysis followed by alkyl chloride then chloro benzene why?
- 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