Chapter 20, Problem 20.28P

Interpretation Introduction

(a)

Interpretation:

The product for the reaction between $\text{methyl cyclohexylmethanoate}$ and $\text{NaOH}$, then ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$, is to be predicted. If no reaction occurs, “no reaction” is to be written. The complete detailed mechanism is to be written if the reaction does occur.

Concept introduction:

The reaction in which one form of an ester is converted to another form by changing the carbon skeleton of the alkoxide part (OR) of the ester is called transesterification. The transesterification reaction is a nucleophilic addition-elimination reaction. In the first step, the nucleophile adds the electro-poor carbonyl carbon of the ester, which forces the bonding pair of carbonyl p bond onto the O atom. A negative charge is produced on that O, and a tetrahedral intermediate is formed. In the second step, tetrahedral intermediate undergoes nucleophilic elimination to form the transesterification product. The transesterification is a reversible reaction. The base hydrolysis of an ester to produce corresponding carboxylic acid and alcohol is called a saponification reaction. Saponification also involves a reversible nucleophilic addition-elimination reaction. The first step in saponification is the same as in the transesterification reaction in which the tetrahedral intermediate is formed. In the second step, nucleophilic elimination takes place to produce an alkoxide ion and the corresponding carboxylic acid. The alkoxide ion rapidly irreversibly deprotonates the carboxylic acid, leading to form the carboxylate ion and alcohol. Finally, on acid workup step, carboxylic acid is regenerated.

Answer to Problem 20.28P

The product for the reaction between $\text{methyl cyclohexylmethanoate}$ and $\text{NaOH}$, then ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$, is

The complete detailed, mechanism for the given reaction is

Explanation of Solution

The given reaction is

So this is a saponification reaction of $\text{methyl cyclohexylmethanoate}$. In the first step, the hydroxide ion (${\text{HO}}^{\text{-}}$) attacks the electron-poor carbonyl carbon of $\text{methyl cyclohexylmethanoate}$, which leads to forming the tetrahedral intermediate.

In the second step, nucleophilic elimination takes place to produce an alkoxide ion and corresponding carboxylic acid. These steps are reversible.

In the third step, irreversible deprotonation of the carboxylic acid takes place and the carboxylate ion is formed. Finally, on acid workup step, protonation of the carboxylate ion takes place to form the carboxylic acid.

Thus, the products of the given reaction are

Conclusion

The product is predicted by using transesterification concept and the detailed mechanism is drawn.

Interpretation Introduction

(b)

Interpretation:

The product for the reaction between $\text{methyl cyclohexylmethanoate}$ and ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{ONa}$, ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ is to be predicted. If no reaction occurs, “no reaction” is to be written. The complete detailed mechanism is to be written if the reaction does occur.

Concept introduction:

The reaction in which one form of an ester is converted to another form by changing the carbon skeleton of the alkoxide part (OR) of the ester is called transesterification. The transesterification reaction is a nucleophilic addition-elimination reaction. In the first step, the nucleophile adds the electro-poor carbonyl carbon of the ester, which forces the bonding pair of carbonyl p bond onto the O atom. A negative charge is produced on that O, and a tetrahedral intermediate is formed. In the second step, tetrahedral intermediate undergoes nucleophilic elimination to form the transesterification product. The transesterification is a reversible reaction. The base hydrolysis of an ester to produce corresponding carboxylic acid and alcohol is called a saponification reaction.

Answer to Problem 20.28P

The product for the reaction between $\text{methyl cyclohexylmethanoate}$ and ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{ONa}$, ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ is

The complete detailed, mechanism for the given reaction is

Explanation of Solution

The given reaction is

This is a transesterification reaction of $\text{methyl cyclohexylmethanoate}$ with a propoxide ion (${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{O}}^{\text{-}}$). So the overall reversible nucleophilic addition-elimination reaction takes place. In the first step, the nucleophile (${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{O}}^{\text{-}}$) adds the electro-poor carbonyl carbon of an ester, which forces the bonding pair of carbonyl p bond onto the O atom. A negative charge is produced on that O, and a tetrahedral intermediate is formed.

In the second step, the tetrahedral intermediate undergoes nucleophilic elimination to form the transesterification product.

Thus, the product of the given reaction is

Conclusion

The product is predicted by using transesterification concept and the detailed mechanism is drawn.

Interpretation Introduction

(c)

Interpretation:

The product for the reaction between $\text{methyl cyclohexylmethanoate}$ and ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}\text{OK}$, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}\text{OH}$ is to be predicted. If no reaction occurs, “no reaction” is to be written. The complete detailed mechanism is to be written if the reaction does occur.

Concept introduction:

The reaction in which one form of an ester is converted to another form by changing the carbon skeleton of the alkoxide part (OR) of the ester is called transesterification. The transesterification reaction is a nucleophilic addition-elimination reaction. In the first step, the nucleophile adds the electro-poor carbonyl carbon of the ester, which forces the bonding pair of carbonyl p bond onto the O atom. A negative charge is produced on that O, and a tetrahedral intermediate is formed. In the second step, tetrahedral intermediate undergoes nucleophilic elimination to form the transesterification product. The transesterification is a reversible reaction. The base hydrolysis of an ester to produce corresponding carboxylic acid and alcohol is called a saponification reaction.

Answer to Problem 20.28P

The product for the reaction between $\text{methyl cyclohexylmethanoate}$ and ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}\text{OK}$, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}\text{OH}$ is

The complete detailed, mechanism for the given reaction is

Explanation of Solution

The given reaction is

This is a transesterification reaction of the $\text{methyl cyclohexylmethanoate}$ with a phenoxide ion (${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{O}}^{\text{-}}$). So the overall reversible nucleophilic addition-elimination reaction takes place. In the first step, the nucleophile (${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{O}}^{\text{-}}$) adds the electro-poor carbonyl carbon of an ester, which forces the bonding pair of carbonyl p bond onto the O atom. A negative charge is produced on that O, and a tetrahedral intermediate is formed.

In the second step, tetrahedral intermediate undergoes nucleophilic elimination to form the transesterification product.

Since phenoxide ion (${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{O}}^{\text{-}}$) is more stable (due to resonance) than methoxide ion (${\text{CH}}_{\text{3}}{\text{O}}^{\text{-}}$), the equilibrium favors the reactant side.

Thus, the product of the given reaction is

Conclusion

The product is predicted by using transesterification concept and the detailed mechanism is drawn.