Alkanoic acid
Introduction
- carboxyl group as functional group; carboxylic acid (-COOH)
- physical properties:
(1) colourless liquid, pungent smell, sour taste
(2) higher m.p./b.p. than alkanes because of 2 hydrogen bonds
(3) density generally decreases as relative molecular mass increases
(4) some dissolves in water (because of hydrogen bond)
Preparation of alkanoic acid
(1) Oxidation
- heating alkanol under reflux with acidified potassium dichromate (VI) (O.A.)
- not possible for methanoic acid
(2) Alkaline hydrolysis of esters (saporification)
Acidic properties of alkanoic acid
- its possessing ionizable hydrogen atoms
- ionization in water: ROOH + H2O <===> RCOO- + H3O+
- acid strength depends on:
(1) whether substituents are electron-donating or electron-withdrawing
(2) more electronegative the halogen (F>Cl>Br>I)
(3) distance between substituents and alkanoic acid
(4) higher number of substituents with negative inductive effect
Alkaline properties of alkanoic acid
- the presence of hydroxyl group (-OH)
- may nucleophilic substitution reaction (hydroxyl group replaced by other functional group)
- may undergo condensation reaction (elimination of water molecules)
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