Analysis of Synthetic Routes (Cambridge (CIE) A Level Chemistry): Revision Note

Analysis of synthetic routes

Some reactions of compound A, are shown below

1. Give the structure of compound B and state the type of reaction by which this compound is formed from compound A

2. What are the suitable reagents for reaction 2?

3. Suggest a more effective way to synthesise compound D from compound A

4. What are the possible by-products of reaction 4?

Answer 1

• This is a hydrogenation reaction

  • The benzene ring becomes hydrogenated to form a cyclohexane

• The structure of compound B is:

• The COOH group is unlikely to be reduced by H₂, Pt (s) / Ni (s) in this case

Answer 2

• The ethyl (-CH₂CH₃) side-chain in compound A has been completely oxidised to a carboxylic acid group (-COOH) attached directly to the benzene ring, giving benzene-1,4-dicarboxylic acid

• The reagents for this oxidation to occur are hot alkaline KMnO₄ followed by dilute H₂SO₄

Answer 3

• Compound D contains an ester (-COOCH₃) group which is formed from the esterification reaction between compound A and methanol (CH₃OH)

• By reacting compound A with PCl₅ (or SOCl₂, or PCl₃ and heat), the carboxylic acid (-COOH) group is converted into an acyl chloride (-COCl) group which is more reactive

• The reaction of this acyl chloride with methanol will cause the reaction to occur faster and will give a higher yield of the ester (compound D) as the reaction goes to completion 

Answer 4

• Reaction 4 is a reduction of the carboxylic acid (-COOH) group in compound A to a primary alcohol (R-CH₂OH)

• The by-product of this reduction is water (H₂O)