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Chapter 19: Problem 76

Using your roadmaps as a guide, show how to convert ethanol, formaldehyde, and acetone into racemic ethyl 2-acetyl-5-oxohexanoate. You must use ethanol, formaldehyde, and acetone as the source of all carbon atoms in the target molecule. Show all reagents and all molecules synthesized along the way.

Short Answer

Expert verified
Question: Outline the steps involved in synthesizing racemic ethyl 2-acetyl-5-oxohexanoate from ethanol, formaldehyde, and acetone. Answer: The process includes: 1. Formation of an ester from ethanol via esterification with ethanoic acid and catalytic sulfuric acid. 2. Formation of a carbon-carbon bond between the acetyl group and ester group obtained in step 1 using a Grignard reagent and acetone. 3. Extending the carbon chain by converting the tertiary alcohol obtained in step 2 to a primary amine, which then reacts with formaldehyde to form an imine. 4. Hydrolysis of the imine compound obtained in step 3 to yield racemic ethyl 2-acetyl-5-oxohexanoate.

Step by step solution

01

Formation of an ester from ethanol

To form an ester from ethanol, we will carry out an esterification reaction with ethanoic acid or its anhydride in the presence of catalytic sulfuric acid: CH3CH2OH + CH3COOH --(H2SO4)--> CH3CH2OOCCH3
02

Formation of a carbon-carbon bond

Now we will form a Grignard reagent from the ester obtained in step 1. The Grignard reagent will then react with acetone to form a tertiary alcohol: 1. CH3CH2OOCCH3 + Mg --(ether)--> CH3CH2OMgX, where X is halide (use dry ether to dissolve the Grignard reagent) 2. CH3CH2OMgX + CH3COCH3 --(ether)--> CH3CH2CH(OH)CH2COCH3
03

Extending the carbon chain - formation of imine with formaldehyde

First, we will prepare a primary amine (RNH2) from the tertiary alcohol obtained in step 2, and then react it with formaldehyde to form an imine. For this, we will carry out a two-step process: 1. CH3CH2CH(OH)CH2COCH3 --(SOCl2)--> CH3CH2CH(Cl)CH2COCH3 - convert alcohol to a chloro compound 2. CH3CH2CH(Cl)CH2COCH3 + 2NH3 --(Zn/Hg or Pd-C, reduction)--> CH3CH2CH(NH2)CH2COCH3 + HCl - convert chloro compound to amine 3. CH3CH2CH(NH2)CH2COCH3 + HCHO --(HCl)--> CH3CH2CH = NCH2CH2COCH3 - imine formation with formaldehyde
04

Hydrolysis of the imine to yield the final product

At this point, we will carry out a hydrolysis on the imine compound obtained in step 3 to yield the racemic ethyl 2-acetyl-5-oxohexanoate: CH3CH2CH = NCH2CH2COCH3 --(H3O+)--> CH3CH2CH(OH)CH2CH2COCH3 + NH3 - this reaction yields racemic ethyl 2-acetyl-5-oxohexanoate since hydrolysis of the imine creates a stereocenter that leads to the respective (R)- and (S)-enantiomers in a 1:1 ratio. The final product is racemic ethyl 2-acetyl-5-oxohexanoate, obtained from ethanol, formaldehyde, and acetone as sources of carbon atoms.

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Most popular questions from this chapter

Write a mechanism for the hydrolysis of the following iminium chloride in aqueous HCl.

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