Preparation of Aldehydes and Ketones - UNSOLVED PRACTICE SET

Q7. Write the reaction for the preparation of ethanal from ethanol using PCC. Why is PCC preferred over K₂Cr₂O₇?

Q8. What is ozonolysis? Write the reaction showing the ozonolysis of but-2-ene.

Q9. Write the reaction for the hydration of propyne to give propanone. What catalyst is used?

Q10. What is Rosenmund reduction? Write the reaction for the preparation of benzaldehyde from benzoyl chloride.

Q11. Write the reaction for the preparation of acetophenone from benzene and acetyl chloride. What catalyst is used?

Q12. Your school lab has a bottle of propan-1-ol. How would you convert it to propanal? Write the reaction and name the reagent.

Q13. (a) Describe the preparation of aldehydes from:

(i) Primary alcohols (using PCC)

(ii) Acid chlorides (Rosenmund reduction)

(iii) Nitriles (Stephen reduction)

(iv) Alkenes (ozonolysis)

Write the reactions for each method.

Q14. (a) Describe the preparation of ketones from:

(i) Secondary alcohols

(ii) Acid chlorides (reaction with organocadmium compounds)

(iii) Alkynes (hydration)

(iv) Alkenes (ozonolysis)

Write the reactions for each method.

Q15. (a) Describe the preparation of aromatic aldehydes by:

(i) Gattermann-Koch reaction

(ii) Etard reaction

(iii) Gattermann reaction

Write the reactions and conditions for each.

(b) Why are these methods preferred for preparing aromatic aldehydes over oxidation of benzyl alcohol?

Q16. A student wants to prepare butanal from butan-1-ol.

(a) Write two different methods for this conversion, naming the reagents used in each.

(b) Which method gives better selectivity? Explain why.

(c) If the student starts with 37 g of butan-1-ol (molar mass = 74 g/mol) and obtains 21.6 g of butanal (molar mass = 72 g/mol), calculate the percentage yield.

(d) What are the likely by-products in each method? How can they be minimized?

(e) Why is PCC preferred over K₂Cr₂O₇ for oxidizing primary alcohols to aldehydes?

Q17. The following reactions are used to prepare aldehydes and ketones:

Reaction 1: CH₃CH₂OH + PCC → CH₃CHO

Reaction 2: CH₃CH=CHCH₃ + O₃ → Products (reductive workup)

Reaction 3: CH₃C≡CH + H₂O → CH₃COCH₃ (HgSO₄/H₂SO₄)

Reaction 4: C₆H₅COCl + H₂/Pd-BaSO₄ → C₆H₅CHO

(a) Identify the type of reaction for each.

(b) For Reaction 2, if 28 g of but-2-ene (molar mass = 56 g/mol) is used, calculate the theoretical yield of ethanal (molar mass = 44 g/mol).

(c) For Reaction 3, explain why propyne gives propanone and not propanal.

(d) For Reaction 4, why is BaSO₄ used with Pd? What would happen if pure Pd was used?

(e) A student claims that Reaction 1 can also be carried out using KMnO₄. Is this correct? Explain.

Q18. In a school chemistry lab, students prepare benzaldehyde by different methods.

(a) Write the Gattermann-Koch reaction for the preparation of benzaldehyde from benzene. What are the reagents and conditions?

(b) Another student prepares benzaldehyde by Stephen reduction. Write the reaction starting from benzonitrile.

(c) A third student oxidizes benzyl alcohol using PCC. Write the reaction. Why is the yield lower than the other two methods?

(d) The students compare the three methods in terms of cost, safety, and environmental impact. Which method would you recommend for a school lab and why?

(e) The teacher asks: "Why can't we prepare benzaldehyde by direct oxidation of toluene using KMnO₄?" What is your answer?