Hell-Volhard-Zelinsky (HVZ) Reaction - UNSOLVED PRACTICE SET
Chapter: Aldehydes Ketones and Carboxylic Acids | Topic: Hell Volhard Zelinsky Reaction
HELL-VOLHARD-ZELINSKY (HVZ) REACTION - UNSOLVED PRACTICE SET
Topic: Hell Volhard Zelinsky Reaction
Multiple Choice Questions
Q1. The Hell-Volhard-Zelinsky reaction is used for:
- Halogenation of the carboxyl carbon
- Halogenation of the α-carbon of carboxylic acids
- Decarboxylation of carboxylic acids
- Esterification of carboxylic acids
Q2. In the HVZ reaction, the reagents used are:
- Cl₂ and red phosphorus
- Br₂ and red phosphorus
- I₂ and red phosphorus
- F₂ and red phosphorus
Q3. The first step in the HVZ reaction involves the formation of:
- An acyl bromide
- An α-bromo acid directly
- An ester
- An anhydride
Q4. Which of the following carboxylic acids will NOT undergo HVZ reaction?
- CH₃CH₂COOH
- (CH₃)₃CCOOH
- CH₃COOH
- CH₃CH₂CH₂COOH
Q5. The α-bromo acid obtained from HVZ reaction of propanoic acid can be further converted to:
- An α-amino acid
- An α-hydroxy acid
- Both (a) and (b)
- Neither (a) nor (b)
Q6. The HVZ reaction proceeds through which of the following intermediates?
- Enol form of acyl bromide
- Carbanion
- Free radical
- Carbocation
Short Answer Questions
Q7. Write the complete reaction of acetic acid with Br₂ in the presence of red phosphorus. Name the product formed.
Q8. Why does the HVZ reaction require the presence of red phosphorus along with bromine? What is the role of red phosphorus?
Q9. Explain why the HVZ reaction is specific to α-carbon halogenation and does not occur at the β-carbon or other positions in the carbon chain.
Q10. Can the HVZ reaction be performed with chlorine instead of bromine? If yes, write the reagents required. If no, explain why.
Q11. In India, many students use bromine water in their labs. If a student accidentally adds bromine water directly to propanoic acid without red phosphorus, will the HVZ reaction occur? Explain with reasoning.
Q12. Write the structure of the product formed when 2-methylbutanoic acid undergoes HVZ reaction. Does this product have a chiral centre? Justify your answer.
Long Answer Questions
Q13. Describe the mechanism of the Hell-Volhard-Zelinsky reaction in detail. Explain the four steps involved: formation of acyl bromide, enolization, bromination, and hydrolysis. Use propanoic acid as an example.
Q14. How can the α-bromo carboxylic acid obtained from the HVZ reaction be converted into an α-amino acid? Write the reaction sequence with proper reagents and conditions. Why is this conversion biologically significant?
Q15. Compare the HVZ reaction with the free radical halogenation of alkanes. How are they different in terms of:
(i) Mechanism
(ii) Position of halogenation
(iii) Reagents required
Numerical / Application-Based Problems
Q16. A carboxylic acid 'A' with molecular formula C₄H₈O₂ undergoes HVZ reaction to give compound 'B'. 'B' on treatment with aqueous ammonia gives compound 'C', which on heating gives a solid 'D'. Identify A, B, C, and D. Write all the chemical equations with proper conditions. Calculate the molecular mass of compound 'D'.
Q17. A student performs the HVZ reaction on 7.4 g of butanoic acid using excess Br₂ and red phosphorus. The α-bromo product obtained is then treated with excess NH₃. Calculate:
(i) The mass of α-bromo butanoic acid formed
(ii) The volume of NH₃ gas required at STP for complete conversion to the amino acid
(Atomic masses: C=12, H=1, O=16, Br=80, N=14)
Q18. In a competitive exam preparation, a student is asked to prepare 2-aminopropanoic acid (alanine) starting from ethanoic acid. Design a step-by-step synthetic route using the HVZ reaction as the key step. Write the structure of each intermediate and the reagents/conditions required at each step. How many moles of Br₂ are theoretically required to produce 1 mole of alanine from ethanoic acid?