Question

Which of the following statements relating to the derivatives of carboxylic acids are correct? [R]C(N)=O (a) An amide \(\mathrm{R}-\mathrm{C}_{-\mathrm{N} \mathrm{H}}\) answers all the tests for a primary amine. (b) Among the carboxylic acid derivatives, acid chloride is the most reactive. Aldehydes, Ketones and Carboxylic Acids \(5.57\) (c) Carboxylic acid can be converted to an ester by reacting with alcohol in the presence of a base. (d) Benzoic acid can be converted to methyl benzoate by using diazomethane.

Short answer

a) An amide \(\mathrm{R}-\mathrm{C}_{-\mathrm{N} \mathrm{H}}\) answers all the tests for a primary amine. b) Among the carboxylic acid derivatives, acid chloride is the most reactive. c) Carboxylic acid can be converted to an ester by reacting with alcohol in the presence of a base. d) Benzoic acid can be converted to methyl benzoate by using diazomethane. Answer: Statements (b) and (d) are correct.

Step-by-step solution

Examine statement (a)

Examine the statement: "An amide \(\mathrm{R}-\mathrm{C}_{-\mathrm{N} \mathrm{H}}\) answers all the tests for a primary amine." Amides have the general structure \(\mathrm{R}-\mathrm{C}_{-\mathrm{N} \mathrm{H}}\), while primary amines have the structure \(\mathrm{R}-\mathrm{N}\mathrm{H}_{2}\). Although amides and primary amines both contain nitrogen, they have distinct chemical properties and reactivity. Therefore, amides do not answer all the tests for a primary amine, and statement (a) is incorrect.

Examine statement (b)

Examine the statement: "Among the carboxylic acid derivatives, acid chloride is the most reactive." Carboxylic acid derivatives have the general structure \(\mathrm{R}-\mathrm{C}(=O)-\mathrm{X}\), where \(\mathrm{X}\) can be a halide (acid chlorides), an alkoxide (esters), an amide, or other functional groups. Acid chlorides are highly reactive due to the strong electron-withdrawing effect of the chlorine atom, making the carbonyl carbon more susceptible to nucleophilic attack. Therefore, statement (b) is correct.

Examine statement (c)

Examine the statement: "Carboxylic acid can be converted to an ester by reacting with alcohol in the presence of a base." Esterification is the process by which a carboxylic acid can be converted to an ester by reacting with an alcohol. The reaction requires an acid catalyst, not a base, to facilitate the protonation of the carbonyl oxygen, making the carbon more susceptible to nucleophilic attack by the alcohol. Since the statement mentions the use of a base instead of an acid catalyst, statement (c) is incorrect.

Examine statement (d)

Examine the statement: "Benzoic acid can be converted to methyl benzoate by using diazomethane." Diazomethane, \(\mathrm{C}\mathrm{H}_{2}\mathrm{N}_{2}\), is a highly reactive compound used to convert carboxylic acids to their methyl esters. Upon reaction with diazomethane, benzoic acid can indeed be converted to methyl benzoate. Therefore, statement (d) is correct.

Conclusion

After analyzing all statements, we can conclude that statements (b) and (d) are correct.

Key concepts

Reactivity of Acid Chlorides

Carboxylic acid derivatives come in different forms, and acid chlorides are among them. These derivatives exhibit varying reactivity, which depends on the group attached to the carbonyl carbon. Acid chlorides prove to be the most reactive among them. This heightened reactivity can be attributed to the presence of the chlorine atom. The chlorine is an excellent electron-withdrawing group, which enhances the electrophilicity of the carbonyl carbon by pulling electron density away from it.
This makes the carbonyl carbon highly susceptible to attack by nucleophiles. Because of this, acid chlorides readily participate in reactions with amines, alcohols, and other nucleophiles.
For students and researchers, understanding the reactivity of acid chlorides is essential in synthesizing new compounds and transforming functional groups in organic chemistry.

Esterification Process

The esterification process involves the conversion of carboxylic acids to esters. This process is typically achieved through a reaction with alcohol in the presence of an acid catalyst, commonly sulfuric or hydrochloric acid. The use of an acid catalyst is crucial as it protonates the carbonyl oxygen, making the electrophilic carbon more susceptible to a nucleophilic attack by the alcohol.
Unlike in the original exercise statement, a base is not effective in catalyzing this reaction. It is the acidic environment that facilitates the necessary proton transfers and stabilizes intermediates.

• The process begins with protonation of the carbonyl group.
• Subsequently, the alcohol performs a nucleophilic attack.
• The final step involves deprotonation to complete the ester formation.

By fully understanding this mechanism, students can accurately predict and control ester synthesis in organic reactions.

Amides vs Primary Amines

It's important to recognize that while amides and primary amines share nitrogen in their structures, they differ in many aspects. Amides typically have the structure \( ext{R}- ext{C}(=O)- ext{NH}_2\), while primary amines have the structure \( ext{R}- ext{NH}_2\).
This difference in structure leads to differences in their chemical properties. Amides possess a carbonyl group making them less basic than amines. Because of the resonance stabilization that amides enjoy, their nitrogen atom is less available for chemical reactions compared to primary amines.
As a result, amides do not perform the same chemical tests as primary amines do, such as the Hinsberg test or reaction with \( ext{HCl}\). Understanding these differences is important, especially in the field of medicinal chemistry where the reactivity and stability of nitrogen-containing compounds play a significant role.

Diazomethane Reaction

Diazomethane is a potent reagent often used in organic synthesis for its ability to convert carboxylic acids into their methyl esters efficiently. Its chemical formula is \( ext{CH}_2 ext{N}_2\), and it is well-known for its explosive nature, necessitating careful handling during reactions.
When diazomethane reacts with carboxylic acids, it facilitates the formation of a methyl ester. The reaction involves the formation of a diazonium salt intermediate, which then undergoes nitrogen evolution to yield the desired ester product. For example, benzoic acid reacts with diazomethane to form methyl benzoate.

• This method of methyl ester formation is highly efficient and quick.
• It requires no additional energy or harsh conditions.

Due to its effectiveness, diazomethane is invaluable in research settings where precise modifications to carboxylic acids are needed.