Hydrolysis of Esters - Acid

• The reverse of the esterification reaction is called?hydrolysis
• Ester hydrolysis is a useful reaction for creating biodegradable plastics
• Esters can be?hydrolysed?to reform the carboxylic acid and alcohol or salts of carboxylic acids by using either?dilute?acid?(e.g. sulfuric acid) or?alkali?(e.g. sodium hydroxide) and?heat
• When an ester is?heated under reflux?with?acid?an equilibrium mixture is established, meaning that the hydrolysis reaction is not complete

Ester hydrolysis by dilute acid is a reversible reaction forming carboxylic acid and alcohol

Hydrolysis of Esters - Alkaline

• However,?heating?the ester?under reflux?with?dilute alkali?(e.g. sodium hydroxide) is an?irreversible?reaction as the ester is fully hydrolysed and the reaction goes to completion
• The carboxylic acid produced reacts with excess alkali to form a?carboxylate salt?and?alcohol
• The?sodium?carboxylate?salt requires further?acidification?to turn into a?carboxylic?acid
  • The sodium carboxylate (-COO-) ion needs to get protonated by an acid (such as HCl) to form the carboxylic acid (-COOH)

   

Ester hydrolysis by dilute alkali is an irreversible reaction forming a sodium carboxylate salt and alcohol

Table showing Differences in Hydrolysis of Esters

Answer:

Answer 1:?Ethanoic acid and ethanol

CH3COOCH2CH3?+ H2O ? CH3COOH + CH3CH2OH

Answer 2:?Sodium propanoate and methanol

CH3CH2COOCH3?+ NaOH → CH3CH2COONa + CH3OH

Ethanoic acid derivatives

Answer:

• Acyl chlorides?are?reactive?organic compounds that undergo many reactions such as?nucleophilic addition-elimination?reactions
• In nucleophilic addition-elimination reactions, the?nucleophilic?addition?of a small molecule across the C=O bond takes place followed by?elimination?of a small molecule
• Examples of these nucleophilic addition-elimination reactions include:
  • Hydrolysis
  • Reaction with alcohols to form?esters
  • Reaction with ammonia and primary amines to form?amides

   

Hydrolysis

• The?hydrolysis?of acyl chlorides results in the formation of a?carboxylic acid?and?HCl?molecule
• This is a?nucleophilic?addition-elimination?reaction
  • A?water molecule?adds across the C=O bond
  • A hydrochloric acid (HCl) molecule is?eliminated

   

• An example is the hydrolysis of propanoyl chloride to form propanoic acid and HCl

Acyl chlorides are hydrolysed to carboxylic acids

Formation of esters

• Acyl chlorides can react with?alcohols?to form esters
• The esterification of acyl chlorides is also a?nucleophilic?addition-elimination?reaction
  • The alcohol adds across the C=O bond
  • A HCl molecule is eliminated

   

Acyl chlorides undergo esterification with alcohols to form esters

Formation of amides

• Acyl chlorides can form?amides?with?primary?amines?and?concentrated?ammonia
• The nitrogen atom in ammonia and primary amine has a lone pair of electrons which can be used to attack the carbonyl carbon atom in the acyl chlorides
• The product is an?amide (when reacted with ammonia) or?N-substituted?amide (when reacted with primary amines)
• This is also an example of a?nucleophilic?addition-elimination?reaction as
  • The amine or ammonia molecule adds across the C=O bond
  • A HCl molecule is eliminated

   

Acyl chlorides undergo reactions with ammonia and primary amines to form amides

• Addition polymerisation has been covered in reactions of alkenes
  • They are made using monomers that have C=C double bonds joined together to form polymers such as polyethene

   

• Condensation polymerisation is another type of reaction whereby a polymer is produced by repeated condensation reactions between monomers
• Natural condensation polymers are all formed by?elimination of water
  • Although the process of?condensation?polymerisation involves the?elimination of a?small molecule

   

• Condensation polymers?can be identified because the monomers are linked by?ester?or?amide bonds

Polyester

• Is formed by the reaction between?dicarboxylic acid monomers?and?diol monomers
• Polyester is produced by linking these monomers with?ester bonds / links

This polymer structure shows an ester functional group linking monomers together

Formation of polyesters

• A diol and a dicarboxylic acid are required to form a polyester
  • A diol contains 2 -OH groups
  • A dicarboxylic acid contains 2 -COOH groups

   

The position of the functional groups on both of these molecules allows condensation polymerisation to take place effectively

• When the polyester is formed, one of the -OH groups on the diol and the hydrogen atom of the -COOH are expelled as a water molecule (H2O)
• The resulting polymer is a polyester
  • In this example, the polyester is?poly(ethylene terephthalate)?or PET, which is sometimes known by its brand names of Terylene or Dacron

   

Expulsion of a water molecule in this condensation polymerisation forms the polyester called (ethylene terephthalate) (PET)

Formation of polyesters - hydroxycarboxylic acids

• So far the examples of making polyesters have focused on using 2 separate monomers for the polymerisation
• There is another route to making polyesters
• A single monomer containing both of the key functional groups can also be used
• These monomers are called hydroxycarboxylic acids
  • They contain an alcohol group (-OH) at one end of the molecule while the other end is capped by a carboxylic acid group (-COOH)

   

Both functional groups that are needed to make the polyester come from the same monomer