26: Carboxylic Acids and their Derivatives

CHAPTER SUMMARY

Carboxylic Acids

• Weak acids, equilibrium lies to the left

• Stronger acids than alcohols

• Acidity: Ethanol < Water < Phenol < Carboxylic Acid

• React with Na and NaOH

Bonds & Acidity

• e- in the C-O bond are drawn away towards the C=O bond

• Carboxylate ion is stabilised by electron delocalisation around the COO- group to spread out the negative charge so that it becomes more stable

• So it becomes less attracted to the H+, and more H+ will be available

• More dissociation so more acidic

Chlorinated Carboxylic Acids

• Cl is electron-withdrawing due to their electronegative nature

• O becomes less negative and the ion becomes more stable

• Less attracted to H+

• More acidic

Oxidation of Carboxylic Acids

• Mild oxidising agents: Fehling’s, Tollen’s reagent

• Strong oxidising agents: Acidified KMnO4 and K2Cr2O7

• HCOOH + [O] —> CO2 + H2O (SOA or MOA)

• HO2C2O2H + [O] —> 2CO2 + H2O (must use SOA)

Acyl Chlorides

• Acyl chloride more reactive than CA since the carbon is more delta positive

• Esterification using acyl chlorides: no need for reflux or catalyst, rtp, producing ester and HCl

• Preparing acyl chloride from benzene:

1. Alkylation of benzene to form methylbenzene

2. Oxidation of methylbenzene to form benzoic acid, by using alkaline NaOH and acidifying it with dilute H2SO4

3. Reaction of benzoic acid with PCl5/PCl3/SOCl2 to form acyl chloride (benzoyl chloride)

• Phenol cannot react with CA (very very slow), but can react with acyl chlorides

• Preparation of Phenol & Diazotisation:

1. NaNO2 + HCl —> NaCl + HNO2

2. C6H5NH2 + HNO2 + HCl —> C6H5N2+Cl- + 2H2O

3. Formation of phenol: C6H5N2+Cl- passed through steam —> phenol + HCl + N2

4. Diazotisation: C6H5N2+Cl- + phenol with NaOH —> C6H5N=NC6H4OH + HCl

• Addition-elimination reaction