Preparation and Properties of Ethers - UNSOLVED PRACTICE SET

Q7. Write the reaction for the preparation of diethyl ether from ethanol. What is the role of concentrated H₂SO₄?

Q8. What is the Williamson ether synthesis? Write the reaction for the preparation of ethyl methyl ether.

Q9. Why are ethers used as solvents in Grignard reactions? What property makes them suitable?

Q10. Why is it dangerous to use old samples of diethyl ether for anesthesia or as a solvent?

Q11. Write the reaction of diethyl ether with HI. Why does the cleavage occur?

Q12. Your teacher shows you that anisole (methoxybenzene) undergoes electrophilic substitution at ortho and para positions. Why does the -OCH₃ group direct substitution to these positions?

Q13. (a) Describe the preparation of ethers by:

(i) Intermolecular dehydration of alcohols

(ii) Williamson ether synthesis

Write the reactions and mention the limitations of each method.

(b) Why is the Williamson synthesis not suitable for preparing tertiary ethers?

Q14. (a) Describe the chemical properties of ethers with respect to:

(i) Reaction with HI

(ii) Reaction with conc. H₂SO₄

(iii) Electrophilic substitution of aromatic ethers

Write one reaction for each.

(b) Explain the mechanism of ether cleavage by HI.

Q15. (a) Explain why ethers are relatively inert chemically.

(b) Why do ethers form peroxides on long standing in air? How can peroxides be detected and removed?

(c) Compare the boiling points of ethers, alcohols, and alkanes of comparable molecular mass. Give reasons.

Q16. A student wants to prepare diethyl ether from ethanol.

(a) Write the reaction for the preparation of diethyl ether from ethanol at 140°C.

(b) If 46 g of ethanol (molar mass = 46 g/mol) is used, calculate the theoretical yield of diethyl ether (C₄H₁₀O, molar mass = 74 g/mol).

(c) In practice, 25.9 g of diethyl ether is obtained. Calculate the percentage yield.

(d) If the temperature is raised to 170°C, what product is formed instead? Calculate the theoretical yield of this product from 46 g of ethanol.

(e) Why is the yield of ether lower than the theoretical yield? (Consider at least two reasons.)

Q17. The following reactions involve ethers:

Reaction 1: C₂H₅OC₂H₅ + HI (excess) → Products

Reaction 2: CH₃OC₆H₅ + HI → Products

Reaction 3: (CH₃)₃C-O-CH₃ + HI → Products

Reaction 4: C₂H₅OC₂H₅ + air (long standing) → Peroxides

(a) Identify the products of Reaction 1, 2, and 3.

(b) For Reaction 1, explain why excess HI is required. What happens with limited HI?

(c) For Reaction 2, why does the cleavage give methyl iodide and phenol, rather than methyl alcohol and iodobenzene?

(d) For Reaction 3, predict the major products and explain the mechanism (SN1 or SN2).

(e) For Reaction 4, why are peroxides dangerous? How can they be detected using KI-starch paper?

Q18. In a school science project, students investigate the uses of ethers in everyday life.

(a) A student finds that her grandfather's old chemistry set contains diethyl ether. Why was diethyl ether used as an anesthetic? Why is it no longer used for this purpose? (Consider flammability and side effects.)

(b) Another student learns that MTBE (methyl tert-butyl ether) is added to petrol. Why is MTBE added? What problem led to its ban in some countries? (Hint: Consider groundwater contamination.)

(c) A third student discovers that crown ethers are used in phase transfer catalysis. What is phase transfer catalysis? Why are 18-crown-6 ethers particularly good at complexing K⁺ ions?

(d) The students learn that THF (tetrahydrofuran) is used as a solvent in polymer chemistry. Why is THF preferred over diethyl ether in some reactions? (Consider boiling point and solubility.)

(e) The teacher asks: "If you were designing a new solvent to replace diethyl ether in laboratories, what properties would you look for? What hazards would you avoid?" Give your answer with reasoning.