Chapter 23, Problem 23.43P

Interpretation Introduction

(a)

Interpretation: The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is to be predicted.

Concept introduction: The Malonic ester synthesis is a method which is used to convert diethyl malonate into a carboxylic acid. $\text{NaOEt}$ is a strong base. It abstracts a proton from the alpha carbon of an ester molecule to forms an enolate ion.

Answer to Problem 23.43P

The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\text{bromo}\left(\text{methoxy}\right)\text{methane}$.

Explanation of Solution

The given carboxylic acid is,

Figure 1

All alkyl groups on the alpha carbon will be obtained from alkyl halides and the remaining molecule is obtained from ethyl acetoacetate. Thus, for the required alkyl halide, the location of alpha carbon is shown below.

Figure 2

Hence, the alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\text{bromo}\left(\text{methoxy}\right)\text{methane}$.

The reaction of diethylmalonate with $\text{bromo}\left(\text{methoxy}\right)\text{methane}$ in the presence of base results in the formation of given carboxylic acid as shown below.

Figure 3

The mechanism involved in the given reaction as follows,

Base abstracts the proton from the alpha carbon and enolate ion reacts with $\text{bromo}\left(\text{methoxy}\right)\text{methane}$ followed by ${\text{S}}_{\text{N}}\text{2}$ mechanism to form product. The product undergoes ester hydrolysis followed by the removal of carbon dioxide and yield keto form. The mechanism is shown below.

Figure 4

Conclusion

The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\text{bromo}\left(\text{methoxy}\right)\text{methane}$.

Interpretation Introduction

(b)

Interpretation: The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is to be predicted.

Concept introduction: The Malonic ester synthesis is a method which is used to convert diethyl malonate into a carboxylic acid. $\text{NaOEt}$ is a strong base. It abstracts a proton from the alpha carbon of an ester molecule to forms an enolate.

Answer to Problem 23.43P

The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\left(\text{1-bromopropan-2-yl}\right)\text{benzene}$.

Explanation of Solution

The given carboxylic acid is,

Figure 5

All alkyl groups on the alpha carbon will be obtained from alkyl halides and the remaining molecule is obtained from ethyl acetoacetate. Thus, for the required alkyl halide, the location of alpha carbon is shown below.

Figure 6

Hence, the alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\left(\text{1-bromopropan-2-yl}\right)\text{benzene}$.

The reaction of diethylmalonate with $\left(\text{1-bromopropan-2-yl}\right)\text{benzene}$ in the presence of base results in the formation of given carboxylic acid as shown below.

Figure 7

The mechanism involved in the given reaction as follows,

Base abstracts the proton from the alpha carbon and enolate reacts with $\left(\text{1-bromopropan-2-yl}\right)\text{benzene}$ followed by ${\text{S}}_{\text{N}}\text{2}$ mechanism to form product. The product undergoes ester hydrolysis followed by the removal of carbon dioxide and yield keto form. The mechanism is shown below.

Figure 8

Conclusion

The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\left(\text{1-bromopropan-2-yl}\right)\text{benzene}$.

Interpretation Introduction

(c)

Interpretation: The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is to be predicted.

Concept introduction: The Malonic ester synthesis is a method which is used to convert diethyl malonate into a carboxylic acid. $\text{NaOEt}$ is a strong base. It abstracts a proton from the alpha carbon of an ester molecule to forms an enolate.

Answer to Problem 23.43P

The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\text{1-bromobutane}$.

Explanation of Solution

The given carboxylic acid is,

Figure 9

All alkyl groups on the alpha carbon will be obtained from alkyl halides and the remaining molecule is obtained from ethyl acetoacetate. Thus, for the required alkyl halide, the location of alpha carbon is shown below.

Figure 10

Hence, the alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\text{1-bromobutane}$.

The reaction of diethylmalonate with $\text{1-bromobutane}$ in the presence of base results in the formation of given carboxylic acid as shown below.

Figure 11

The mechanism involved in the given reaction as follows,

Base abstracts the proton from the alpha carbon and enolate reacts with $\text{1-bromobutane}$ followed by ${\text{S}}_{\text{N}}\text{2}$ mechanism to form product $\left(\text{I}\right)$. Again, base abstracts the proton from the alpha carbon of product $\left(\text{I}\right)$ and enolate reacts with $\text{1-bromobutane}$ followed by ${\text{S}}_{\text{N}}\text{2}$ mechanism to form product $\left(\text{II}\right)$. The product $\left(\text{II}\right)$ undergoes ester hydrolysis followed by the removal of carbon dioxide and yield keto form. The mechanism is shown below.

Figure 12

Conclusion

The alkyl halide which is needed to prepare given carboxylic acid using the malonic ester synthesis is $\text{1-bromobutane}$.