Organic Chemistry Multiple Choice Questions on “Preparation of Ethers”.
1. Chloroethane reacts with X to form diethyl ether. What is X?
a) NaOH
b) H2SO4
c) C2H5ONa
d) Na2S2O3
Answer: c
Clarification: The reaction of sodium ethoxide with chloroethane to form diethyl ether and sodium chloride:
[Na]+[C2H5O]– + C2H5Cl → C2H5OC2H5 + [Na]+[Cl]–
2. The reaction given below is known as by which o the following reaction?
C2H5ONa+IC2H5→C2H5OC2H5+NaI
a) Kolbe’s synthesis
b) Wurtz’s synthesis
c) Williamson’s synthesis
d) Grignard’s synthesis
Answer: c
Clarification: Williamson Ether Reactions involve an alkoxide that reacts with a primary haloalkane or a sulfonate ester. Alkoxides consist of the conjugate base of an alcohol and are comprised of an R group bonded to an oxygen atom. They are often written as RO–, where R is the organic substituent.
3. The Williamson ether synthesis produces ethers by reacting which of the following?
a) alcohol with a metal
b) alkoxide with a metal
c) alkoxide with an alkyl halide
d) alkyl halide with an aldehyde
Answer: c
Clarification: It’s a type of reaction we’ve already seen many times before – an SN2 reaction between a deprotonated alcohol [“alkoxide”] and an alkyl halide that forms an ether.
4. In which case would a Williamson ether synthesis fail?
a) sodium ethoxide + iodomethane
b) sodium ethoxide + iodoethane
c) sodium ethoxide + 2-iodopropane
d) sodium ethoxide + 2-iodo-2-methylpropane
Answer: d
Clarification: Because alkoxides are strong bases, competition with elimination [E2] pathways becomes a concern once the alkyl halide becomes more sterically hindered. For this reason, trying to perform a Williamson on a secondary alkyl halide is a bit more problematic than it is for a primary alkyl halide.
5. Which of the following reagents should be used to prepare tert-butyl ethyl ether?
a) tert-butyl bromide and sodium ethoxide
b) tert-butyl alcohol and ethyl bromide
c) tert-butyl alcohol and ethanol
d) potassium tert-butoxide and ethyl bromide
Answer: d
Clarification: When ethyl bromide(CH3CH2Br) is added to potassium tert-butoxide ((CH3)3-O– + K), the product is ethyl tert-butyl ether(CH3)3-O-CH2CH3).
CH3CH2Br + (CH3)3-O– + K → (CH3)3-O-CH2CH3.
6. Which of the following reagents should be used to prepare tert-butyl propyl ether?
a) 2-methylpropene and 1-propanol
b) 2-methylpropene, acetic acid and 1-propanol
c) 2-methylpropene, H2SO4 and 1-propanol
d) 1-propyl bromide and tert-butyl alcohol
Answer: c
Clarification: The dehydration reaction of alcohols to generate alkene proceeds by heating the alcohols in the presence of a strong acid, such as sulfuric or phosphoric acid, at high temperatures. If the reaction is not sufficiently heated, the alcohols do not dehydrate to form alkenes, but react with one another to form ethers.
7. What will be the reactant and reaction condition required for the given reaction?
CH3CH2OH +? → C2H5OC2H5
a) H2SO4, 413K
b) H2SO4, 443K
c) HNO3, 413K
d) HNO3, 443K
Answer: a
Clarification: In the presence of protic acids (sulphuric acid), alcohols undergo dehydration to produce alkenes and ethers under different conditions. For example: in the presence of sulphuric acid, dehydration of ethanol at 443 K yields ethene whereas it yields ethoxyethane at 413 K. This is an ideal method of preparation through primary alcohols.