[26.4] carboxylic acid derivatives Flashcards
what is a carboxylic acid derivative?
a compound that can be hydrolysed to form the parent carboxylic acid
what are 4 derivatives of carboxylic acids?
- esters
- acyl chlorides
- acid anhydrides
- amides
what is esterification?
the reaction of an alcohol with a carboxylic acid to form an ester
esterification: reagents, conditions, product, naming
- reagents: carboxylic acid + alcohol
- conditions: reflux and concentrated sulfuric acid cataylst
- products: ester + water
- naming: -yl from alcohol, -oate from CA
what can esters be prepared from?
- carboxylic acids
- acyl chlorides
- acid anhydrides
describe the reactivity of esters
unreactive compared to acids and acyl chlorides
describe the isomerism of esters
structural isomers of CAs
acid hydrolysis of esters
- reverse of esterification
- form a carboxylic acid + alcohol
- heated under reflux
- dilute HCl (aq) acts as a catalyst (doesn’t go in equation)
- reversible reaction
alkaline hydrolysis of esters
- heated under reflux
- NaOH (aq)
- forms COOH + alcohol but metal ions present (aq) so carboxylate salt produced
what do all carboxylic acid derivatives contain?
- an acyl group (R-C=O)
- an electronegative atom or group of atoms
naming acyl chlorides
- named from ‘parent’ CA
- remove the -oic acid
- replace with -oyl chloride
- structure: C=O and Cl attached to C
eg. ethanoic acid = ethanoyl chloride
making acyl chlorides
- carboxylic acid + thionyl chloride (SOCl₂)
- R-COOH + SOCl₂ -> R-COCl + SO₂ (g) + HCl (g)
conditions for making acyl chlorides
- acyl chlorides must be kept dry as they react with water
- reaction should be carried out in a fume cupboard as products are harmful
reactions of acyl chlorides
- good starting material as it can make lots of functional groups
- acyl chloride group makes it very reactive
- no need for catalyst
- Cl and O are electron-withdrawing, increasing the positivty of C and susceptibility to nucleophilic attack
- corrosive and produce harmful gases (HCl)
what 4 reactions can acyl chlorides undergo to form?
- esters
- carboxylic acids
- primary amides
- secondary amides
reaction of acyl chlorides to form esters
- acyl chloride + alcohol -> ester + HCl (g)
- room temperature
- irreversible reaction
- HCl - misty fumes observed
reaction of acyl chlorides to form carboxylic acids
- acyl chloride + water -> carboxylic acid + HCl (g)
- vigourous at room temperature
- HCl - misty fumes observed
reaction of acyl chlorides to form primary amides
- acyl chloride + ammonia (NH₃) -> (1) amide + NH₄Cl
- does produce HCl but HCl + excess NH₃ -> NH₄⁺Cl⁻
- violent reaction producing white smoke
reaction of acyl chlorides to form secondary amides
- acyl chloride + primary amine -> N-amide + CH₃NH₃⁺Cl⁻
- violent reaction producing a white solid mixture
- does produce HCl but HCl + excess primary amine -> CH₃NH₃⁺Cl⁻
why is using acyl chlorides to make esters preferable to COOH + alcohol?
- irreversible so better yield
- no need for catalyst: happens ar room temp
- reacts with phenol (COOH too weak)
reactions of acid anhydrides compared to reactions of acyl chlorides
- react in a similar way to acyl chlorides but are less exothermic, less corrosive and safer
- cheaper
- less reactive than acyl chlorides (less electron-withdrawing effect) so reactions are slower
- requires gentle heating
- instead of HCl as a product, makes R-COOH
describe the structure and naming of acid anhydrides
- symmetrical molecule
- O in middle, C=O attached to either side
- -R attached to C
- to name, basically split molecule in half and see which parent CA eg. ethanoic anhydride
reaction of acid anhydrides to form esters
- acid anhydride + alcohol -> ester + carboxylic acid
- CA is safer than HCl
reasons why use of acid anhydrides is favoured over corresponding acyl chlorides
acyl chlorides are:
- difficult to hand as they react very readily with water so need to be used in water-free conditions
- react to produce corrosive HCl
acid anhydrides are:
- cheaper to produce
- no as moisture sensitive
- less corrosive
- produce carboxylic acids, which are safer than HCl
