Chapter 20, Problem 20.27AP

Interpretation Introduction

(a)

Interpretation:

The product formed when butyric acid reacts with ethanol in the presence of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ catalyst is to be stated.

Concept introduction:

Esterification occurs when a carboxylic acid reacts with an alcohol in the presence of an acid catalyst. Esters end with a suffix, $-oate$. They are always present in the middle of the carbon chain.

Answer to Problem 20.27AP

The product formed when butyric acid reacts with ethanol in the presence of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ catalyst is shown below.

Explanation of Solution

When butyric acid reacts with ethanol in the presence of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ catalyst, an ester, ethyl butyrate is formed. The reaction occurs with the release of a water molecule. The complete reaction is shown below.

Figure 1

Conclusion

When butyric acid reacts with ethanol in presence of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ catalyst, an ester, ethyl butyrate is formed.

Interpretation Introduction

(b)

Interpretation:

The product formed when butyric acid reacts with aqueous $\text{NaOH}$ solution is to be stated.

Concept introduction:

An acid-base reaction occurs through a transfer of proton from an acid to a base. The base gets protonated and the acid gets deprotonated. The reaction results in the formation of a conjugate acid and a conjugate base as the products. The type of products formed affects the direction of reaction at equilibrium.

Answer to Problem 20.27AP

The product formed when butyric acid reacts with aqueous $\text{NaOH}$ solution is shown below.

Explanation of Solution

When a carboxylic acid reacts with a base, the hydrogen atom is abstracted by the base and a salt of carboxylic acid is formed.

So, when butyric acid reacts with aqueous $\text{NaOH}$ solution, sodium salt of butyric acid, sodium butyrate, is formed as shown below.

Figure 2

Conclusion

The product formed when butyric acid reacts with aqueous $\text{NaOH}$ solution is sodium butyrate.

Interpretation Introduction

(c)

Interpretation:

The product formed when butyric acid reacts with ${\text{LiAlH}}_{\text{4}}$ (excess), and then ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is to be stated.

Concept introduction:

The substances which on addition removes oxygen atom or hydrogen atom from the other substance, that is, reduces the other substances are known as reducing agents. Reducing agents themselves get oxidized. Carboxylic acid is reduced when reacts with reducing agent, ${\text{LiAlH}}_{\text{4}}$ into aldehydes or ketones. When excess of ${\text{LiAlH}}_{\text{4}}$ is used, carboxylic acid is reduced to an alcohol.

Answer to Problem 20.27AP

The product formed when butyric acid reacts with ${\text{LiAlH}}_{\text{4}}$ (excess), then ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is shown below.

Explanation of Solution

Carboxylic acid is reduced when reacts with reducing agent, ${\text{LiAlH}}_{\text{4}}$ into aldehydes or ketones. When excess of ${\text{LiAlH}}_{\text{4}}$ is used, carboxylic acid is reduced to an alcohol.

When butyric acid reacts with excess of ${\text{LiAlH}}_{\text{4}}$ and then hydrolyzed, it is reduced to $\text{1-butanol}$ as shown below.

Figure 3

Conclusion

When butyric acid reacts with excess of ${\text{LiAlH}}_{\text{4}}$ and then hydrolyzed, it is reduced to $\text{1-butanol}$.

Interpretation Introduction

(d)

Interpretation:

The product formed when butyric acid is heated is to be stated.

Concept introduction:

Carboxylic acids such as $\text{β-}$ keto carboxylic acids, or dicarboxylic acids, decompose on heating. The product formed is either an anhydride or decarboxylated product. Simple carboxylic acids with no electron withdrawing groups attached to them do not give any reaction on heating.

Answer to Problem 20.27AP

When butyric acid is heated, no product is formed.

Explanation of Solution

The structure of butyric acid does not have any electron-withdrawing group like $\text{β-}$ keto group; therefore, no reaction will occur on heating because the normal carboxylic acids are stable. But $\text{β-}$ keto carboxylic acids are unstable. The $\text{β-}$ keto carboxylic acids decarboxylates on heating the keto group bonds with the carboxy hydrogen to form a transition state consisting of six atoms in cyclic pattern. The transition state decomposes into enol which tautomerises into ketone.

Conclusion

Butyric acid on heating gives no reaction.

Interpretation Introduction

(e)

Interpretation:

The product formed when butyric acid reacts with ${\text{SOCl}}_{\text{2}}$ is to be stated.

Concept introduction:

Carboxylic acids react with ${\text{SOCl}}_{\text{2}}$ to form acid chlorides. The hydroxyl group of carboxylic acid attacks the sulfur of ${\text{SOCl}}_{\text{2}}$, which release a chloride ion and the hydroxyl group becomes a good leaving group. The chloride ion released attacks the carbon atom by ${\text{S}}_{\text{N}}\text{2}$ mechanism and forms an acid chloride with inversion of configuration.

Answer to Problem 20.27AP

The product formed when butyric acid reacts with ${\text{SOCl}}_{\text{2}}$ is shown below.

Explanation of Solution

When butyric acid reacts with ${\text{SOCl}}_{\text{2}}$, the hydroxyl group of butyric acid attacks the sulfur of ${\text{SOCl}}_{\text{2}}$, which release a chloride ion and the hydroxyl group becomes a good leaving group. The chloride ion released attacks the carbon atom by ${\text{S}}_{\text{N}}\text{2}$ mechanism and forms an acid chloride, butanoyl chloride, with inversion of configuration.

Figure 4

Conclusion

The product formed when butyric acid reacts with ${\text{SOCl}}_{\text{2}}$ is butanoyl chloride.

Interpretation Introduction

(f)

Interpretation:

The product formed when butyric acid reacts with diazomethane in ether is to be stated.

Concept introduction:

Esterification occurs when carboxylic acid reacts with diazomethane in ether. Esters end with a suffix, $-oate$. They are always present in the middle of the carbon chain.

Answer to Problem 20.27AP

The product formed when butyric acid reacts with diazomethane in ether is shown below.

Explanation of Solution

Esterification occurs when butyric acid reacts with diazomethane in ether and methyl butyrate is formed as a product along with the release of nitrogen gas. The complete reaction is shown below.

Figure 5

Conclusion

The product formed when butyric acid reacts with diazomethane in ether is methyl butyrate.

Interpretation Introduction

(g)

Interpretation:

The product formed when $1\text{-butanol}\left(\text{excess}\right)$ reacts with ${\text{CH}}_{\text{3}}\text{CH}=\text{O}+\text{HCl}\text{catalyst}$ is to be stated.

Concept introduction:

Acetal is formed when an alcohol in excess reacts with an aldehyde or ketone in acidic medium. The rate of reaction increases in acidic medium. The aldehyde gets protonated in acidic medium.

Answer to Problem 20.27AP

The product formed when $1\text{-butanol}\left(\text{excess}\right)$ reacts with ${\text{CH}}_{\text{3}}\text{CH}=\text{O}+\text{HCl}\text{catalyst}$ is shown below.

Explanation of Solution

When an alcohol reacts with an aldehyde in presence of an acid catalyst, a hemiacetal is formed as an intermediate which further reacts to produce acetal with the release of water. The acidic catalyst is used because the alcohol is a weak nucleophile. So on addition of an acid, the oxygen of aldehyde gets protonated and a carbocation is formed. The alcohol easily attacks the carbocation to form the germinal diether derivative of aldehyde, that is, an acetal. When $1\text{-butanol}\left(\text{excess}\right)$ reacts with ${\text{CH}}_{\text{3}}\text{CH}=\text{O}$ in presence of $\text{HCl}$, an acetal, $\text{1-}\left(\text{1-butoxyethoxy}\right)\text{butane}$, is formed as shown below.

Figure 6

Conclusion

When $1\text{-butanol}\left(\text{excess}\right)$ reacts with ${\text{CH}}_{\text{3}}\text{CH}=\text{O}$ in presence of $\text{HCl}$, an acetal, $\text{1-}\left(\text{1-butoxyethoxy}\right)\text{butane}$, is formed.

Interpretation Introduction

(h)

Interpretation:

The product formed when butanoyl chloride reacts with benzene in ${\text{AlCl}}_{\text{3}}$ and then with ${\text{H}}_{\text{2}}\text{O}$ is to be stated.

Concept introduction:

Friedel crafts acylation reaction is a reaction in which an aromatic compound is reacted with an acyl chloride in presence of a Lewis acid to form an aromatic ketone. This reaction takes place by electrophilic substitution reaction mechanism.

Answer to Problem 20.27AP

The product formed when butanoyl chloride reacts with benzene in ${\text{AlCl}}_{\text{3}}$ and then with ${\text{H}}_{\text{2}}\text{O}$ is shown below.

Explanation of Solution

Benzene undergoes Friedel Crafts acylation reaction on reaction with butanoyl chloride in presence of ${\text{AlCl}}_{\text{3}}$, followed by hydrolysis to yield $\text{1-phenyl-1-butanone}$. The complete reaction is shown below.

Figure 7

Conclusion

The product formed when butanoyl chloride reacts with benzene in ${\text{AlCl}}_{\text{3}}$ and then with ${\text{H}}_{\text{2}}\text{O}$ is $\text{1-phenyl-1-butanone}$.

Interpretation Introduction

(i)

Interpretation:

The product formed when $\text{1-phenyl-1-butanone}$ reacts with ${\text{H}}_{\text{2}}{\text{NNH}}_{\text{2}}$ in $\text{KOH}$, and ethylene glycol (solvent), and then heated is to be stated.

Concept introduction:

Wolff Kishner Reduction is a reaction in which aldehydes and ketones are converted into alkanes on reaction with hydrazine, $\text{KOH}$, and on heating. Carbonyl compound is condensed on heating with hydrazine to form hydrazone. The base, $\text{KOH}$ reduces the carbon into alkane and oxidizes the hydrazine to nitrogen gas.

Answer to Problem 20.27AP

The product formed when $\text{1-phenyl-1-butanone}$ reacts with ${\text{H}}_{\text{2}}{\text{NNH}}_{\text{2}}$ in $\text{KOH}$, and ethylene glycol (solvent), and then heated is shown below.

Explanation of Solution

Wolff Kishner reduction takes place when $\text{1-phenyl-1-butanone}$ reacts with ${\text{H}}_{\text{2}}{\text{NNH}}_{\text{2}}$ to form a hydrazone intermediate. The hydrazone reacts with base, $\text{KOH}$, and ethylene glycol (solvent), and then heated to form a saturated product, butylbenzene, as shown below.

Figure 8

Conclusion

The product formed when $\text{1-phenyl-1-butanone}$ reacts with ${\text{H}}_{\text{2}}{\text{NNH}}_{\text{2}}$ in $\text{KOH}$, and ethylene glycol (solvent), and then heated is butylbenzene.