Carboxylic Acids Flashcards
Preparation of Carboxylic Acids
- oxidation from primary alcohol
- oxidation from aldehyde
- oxidation from alkyl benzene
- oxidative cleavage from alkenes
- hydrolysis from nitriles(acid hydrolysis, base hydrolysis)
- hydrolysis from esters(acid hydrolysis, base hydrolysis)
- hydrolysis from amides(acid hydrolysis, base hydrolysis)
- hydrolysis from acid chlorides
Reactions of Carboxylic Acids
- Formation of salts
— Reaction with metals*(Na,Mg)
— Reaction with NaOH
— Reaction with Na2CO3/NaHCO3 - Formation of ester
- Formation of acyl chlorides *(PCl3, PCl5, SOCl2
- Formation of primary alcohol
- Oxidation of Methanoic acid and Ethanedioic acid
Acidity of Carboxylic Acids(THE BIG IDEA)
- the strength of acid depends on stability of anion
- anion is stabilised if negative charge is dispersed
- more stable the anion, the greater extent of acid dissociation, stronger the acid
How are Carboxylic Acids acidic
- in carboxylic acid
- the p-orbital of the C atom overlaps sideways with the p orbitals of the 2 neighbouring O atoms
- the negative charge on the carboxylate ion is distributed equally between the two O atoms
- dispersal of the negative charge results in the stability of the carboxylate ion
- dissociation of acid to release H+ is favoured
What are the Carboxylic Acid Derivatives
- Esters
- Acid chlorides
- Amides
Reactions of Esters
- Hydrolysis(acid hydrolysis, base hydrolysis)
- Reduction of ester
- Condensation Polymerisation
Why are acid chlorides very reactive
- there are two highly electron-withdrawing atoms Cl and O bonded to the acyl carbon atom
- this makes the carbon atom of the acyl chloride extremely electron-deficient
- the carbon is very susceptible to reaction with nucleophiles and undergo nucleophilic substitution readily
Reactions of Acid Chlorides
- nucleophilic substitution reaction with water
- formation of esters
— acid chlorides with alcohols
— acid chlorides with phenol - nucleophilic substitution reaction to form amide
Why phenol cannot react with carboxylic acid to form ester
- phenol is a weaker nucleophile than alcohol
- as lone pair of electrons on the oxygen is delocalised into the benzene ring
- it is not nucleophilic enough to react with carboxylic acid to form ester
Why can alcohol react with acid chloride to form ester under a milder condition as compared to reaction with carboxylic acid?
— in carboxylic acid
- overlap of 2p orbital of the C atom with the 2p orbitals of the two neighbouring O atoms is more effective
- delocalisation of lone pair of electron from O atom is more effective
- C is less electron deficient and less susceptible to reaction with a nucleophile
— in acid chloride
- overlap of 2p orbital of the C atom with the 3p orbital of the Cl atom is less effective
- delocalisation of lone pair of electron from Cl atom is less effective
- C is more electron deficient and more susceptible to a reaction with a nucleophile
Relative ease of hydrolysis of acid chloride
- most reactive
- the carbon of the acyl group is highly electro-deficient because it is bonded to 2 highly electronegative atoms, oxygen and chlorine
- carbon is very susceptible to reaction with nucleophiles
- H2O, weak nucleophile can hydrolyse it
Relative ease of hydrolysis of alkyl chloride
- carbon atom is bonded to only one electronegative atom, chlorine
- carbon is less electron deficient
- stronger nucleophile ,OH- , with heat under reflux condition is required for hydrolysis
Relative ease of hydrolysis of aryl chloride
- no reaction
- lone pair on Cl can delocalise into the pi electron cloud of the benzene ring
- the C-Cl bond, having partial double bond character, is stronger and the carbon atom is also less electron-deficient
Distinguishing test for acid chlorides, alkyl chlorides, aryl chlorides
- Aqueous AgNO3, warm
- acid chloride: white precipitate appears instantly
- alkyl chloride: slower appearance of white precipitate
- aryl chloride: no white precipitate
