Problem 22-4 A student intends to carry out the following synthesis: CH2Ph (1) b

Question

Problem 22-4 A student intends to carry out the following synthesis: CH2Ph (1) base (2) PhCH,Br He adds sodium ethoxide to cyclohexanone (in ethanol solution) to make the enolate ion: then he adds benzyl bromide to alkylate the enolate ion, and heats the solution for half an hour to drive the reaction to completion. Part A Explain why the Williamson ether synthesis will occur. Match the words in the left column to the appropriate blanks in the sentences on the right. Reset Help a tiny amount Sodium ethoxide is not a strong enough base to deprotonate cyclohexanone more than a of the NaOEt is still present when benzyl Since approximately 20% by Williamson ether synthesis. Unreacted cyclohexanone bromide is added, these two 50%. will remain in the reaction solution. 99.99 80 eac will not react

Explanation / Answer

PART (A)

Sodium ethoxide is not strong enough base to deprotonate more than 20%.since approximately 80 % of the sodium ethoxide is till present when benzyl bromide is added, these two react by Williamson ether synthesis, Unreacted cyclohexanone will remain the solution.

PART (B)

C6H5-CH2-Br + NaOEt ---------------> C6H5-CH2-OEt + NaBr

PART(C)

Two changes are needed to make the desired reaction feasible:

I1) Use a strong nucleophilic base such as LDA that will completely deporotnate cyclohexanone and

(2) use an aprotic solvent as THF or diethyl ether sothat cyclohexanone cannot find a proton from solvent. These conditions will work fine.

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