Sometimes a target compound cannot be made from the starting material in one step. A two-stage synthetic route converts the starting material into an intermediate, which is then converted into the product. For each stage, give the reagents and conditions and name the intermediate.Useful AS reactions:
• alkene + steam, H3PO4 catalyst → alcohol
• alkene + HBr → bromoalkane
• haloalkane + NaOH(aq), heat under reflux → alcohol
• primary alcohol + H2SO4/K2Cr2O7: distil → aldehyde; excess oxidant, heat under reflux → carboxylic acid
• secondary alcohol + H2SO4/K2Cr2O7, heat under reflux → ketone
• alcohol + acid catalyst (H2SO4 or H3PO4), heat → alkene
• alcohol + NaBr/H2SO4, heat → bromoalkaneWork backwards from the target: which functional group does it have, which reaction makes that group, and what must the starting material for that reaction be? That compound is your intermediate.Worked example: make propanoic acid from 1-bromopropane.
Stage 1: 1-bromopropane + aqueous sodium hydroxide, heat under reflux → propan-1-ol (nucleophilic substitution).
Stage 2: propan-1-ol + excess acidified potassium dichromate(VI), heat under reflux → propanoic acid (oxidation); orange turns green.Similarly, propanone can be made from propene: steam hydration gives propan-2-ol (the major product), which is then oxidised to propanone.None of these reactions changes the number of carbon atoms, so the starting material and product must have the same chain length.
• alkene + steam, H3PO4 catalyst → alcohol
• alkene + HBr → bromoalkane
• haloalkane + NaOH(aq), heat under reflux → alcohol
• primary alcohol + H2SO4/K2Cr2O7: distil → aldehyde; excess oxidant, heat under reflux → carboxylic acid
• secondary alcohol + H2SO4/K2Cr2O7, heat under reflux → ketone
• alcohol + acid catalyst (H2SO4 or H3PO4), heat → alkene
• alcohol + NaBr/H2SO4, heat → bromoalkaneWork backwards from the target: which functional group does it have, which reaction makes that group, and what must the starting material for that reaction be? That compound is your intermediate.Worked example: make propanoic acid from 1-bromopropane.
Stage 1: 1-bromopropane + aqueous sodium hydroxide, heat under reflux → propan-1-ol (nucleophilic substitution).
Stage 2: propan-1-ol + excess acidified potassium dichromate(VI), heat under reflux → propanoic acid (oxidation); orange turns green.Similarly, propanone can be made from propene: steam hydration gives propan-2-ol (the major product), which is then oxidised to propanone.None of these reactions changes the number of carbon atoms, so the starting material and product must have the same chain length.