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A student wanted to use the Williamson ether synthesis to make (R)-2-ethoxybutane. He
Chapter 11, Problem PROBLEM 11-35(choose chapter or problem)
A student wanted to use the Williamson ether synthesis to make (R)-2-ethoxy butane. He remembered that the Williamson synthesis involves an \(\rm{S}_\rm{N}2\) displacement, which takes place with the inversion of configuration. He ordered a bottle of (S)-butan-2-ol for his chiral starting material. He also remembered that \(\rm{S}_\rm{N}2\) goes best on primary halides and tosylates, so he made ethyl tosylate and sodium (S)-but-2-oxide. After warming these reagents together, he obtained an excellent yield of 2-ethoxy butane.
a. What enantiomer of 2-ethoxy butane did he obtained? Explain how this enantiomer results from the \(\rm{S}_\rm{N}2\) reaction of ethyl tosylate with sodium (S)-but-2-oxide.
b. What would have been the best synthesis of (R)-2-ethoxy butane?
c. How can this student convert the rest of his bottle of (S)-butan-2-ol to (R)-2-ethoxy butane?
Questions & Answers
QUESTION:
A student wanted to use the Williamson ether synthesis to make (R)-2-ethoxy butane. He remembered that the Williamson synthesis involves an \(\rm{S}_\rm{N}2\) displacement, which takes place with the inversion of configuration. He ordered a bottle of (S)-butan-2-ol for his chiral starting material. He also remembered that \(\rm{S}_\rm{N}2\) goes best on primary halides and tosylates, so he made ethyl tosylate and sodium (S)-but-2-oxide. After warming these reagents together, he obtained an excellent yield of 2-ethoxy butane.
a. What enantiomer of 2-ethoxy butane did he obtained? Explain how this enantiomer results from the \(\rm{S}_\rm{N}2\) reaction of ethyl tosylate with sodium (S)-but-2-oxide.
b. What would have been the best synthesis of (R)-2-ethoxy butane?
c. How can this student convert the rest of his bottle of (S)-butan-2-ol to (R)-2-ethoxy butane?
ANSWER:Step 1 of 5
Williamson ether synthesis involves the formation of an ether incorporating an alkyl halide and alcohol.
The reaction proceeds through a concerted \(\rm{S_N2}\) mechanism where the attack of the nucleophile takes place from the backside of the electrophilic carbon.