Question

Which of the following statements relating to the derivatives of carboxylic acids are correct? (a) An amide \(\mathrm{R}-\mathrm{C}\), answers all the tests for a primary amine. (b) Esters undergo hydrolysis more readily than acid amides.. (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 shows similar properties and reactivity as a primary amine. b. An ester is more prone to undergo hydrolysis than an amide. c. Carboxylic acids can be converted to esters in the presence of bases. d. Benzoic acid can be converted to methyl benzoate using diazomethane. Answer: b, d

Step-by-step solution

Statement (a)

An amide \(\mathrm{R}-\mathrm{C}\) refers to a structure where \(\mathrm{R}\) is the organic group and \(\mathrm{C}\) is the carbonyl group. An amide has a general structure \(\mathrm{RCONR_2}\), where \(\mathrm{R_2}\) can be either hydrogen or another organic group. A primary amine, which has the general structure \(\mathrm{RNH_2}\), can show different properties and reactivity compared to an amide. Since amides have a carbonyl group, they are less basic and less nucleophilic than primary amines. Therefore, the statement (a) is incorrect.

Statement (b)

Esters have the general structure \(\mathrm{RCOOR'}\), while acid amides (also known as amides) have the general structure \(\mathrm{RCONR_2}\). Due to the presence of the electron-donating oxygen atom in esters, they are more reactive to nucleophiles than amides, and thus, undergo hydrolysis more readily. This occurs because the carbonyl group of an ester is more electrophilic than that of an amide, causing it to be more prone to nucleophilic attack. Therefore, statement (b) is correct.

Statement (c)

Carboxylic acids have the general structure \(\mathrm{RCOOH}\), and they can be converted into esters \(\mathrm{RCOOR'}\) by reacting with alcohols in the presence of an acid catalyst, not a base. The reaction requires protonation of the carbonyl oxygen atom in the carboxylic acid moiety, which cannot occur in the presence of a base. Instead, in the presence of a base, the carboxylate ion is formed due to deprotonation of the carboxylic acid, and esterification does not occur. Thus, statement (c) is incorrect.

Statement (d)

Benzoic acid is a carboxylic acid having the structure \(\mathrm{C_6H_5COOH}\). Methyl benzoate has the structure \(\mathrm{C_6H_5COOCH_3}\). Diazomethane (\(\mathrm{CH_2N_2}\)) is a highly reactive compound that can act as a methylation agent. It can be used to convert benzoic acid into methyl benzoate by reacting with the carboxylic acid group. The mechanism involves the nucleophilic attack of diazomethane on the carbonyl carbon of benzoic acid, followed by the elimination of nitrogen gas, ultimately forming methyl benzoate. Therefore, statement (d) is correct. In conclusion, statements (b) and (d) are correct, while statements (a) and (c) are incorrect.

Key concepts

Amides and Amines

Amides and amines are two distinct types of carboxylic acid derivatives, differing mainly in their composition and chemical behavior. An amide is composed of a carbonyl group bonded to a nitrogen atom, typically having the structure \(\mathrm{RCONR_2}\). The nitrogen atom can be bonded to either hydrogen atoms or organic groups.

Conversely, amines are not directly derived from carboxylic acids; they contain nitrogen bonded to a carbon chain and generally have the structure \(\mathrm{RNH_2}\). While amides contain a carbonyl group that influences their properties, amines do not, making them exhibit different chemistry.

• Reactivity: Amides are less reactive than amines due to the presence of the carbonyl group. The electron withdrawing effect makes the nitrogen in amides less basic and less nucleophilic.
• Basicity: Amines are more basic than amides without the influence of the electron-withdrawing carbonyl group, making them more likely to accept protons.

Esterification Reactions

Esterification is the chemical reaction that forms an ester \(\mathrm{RCOOR'}\) from a carboxylic acid and an alcohol. This process typically requires an acid catalyst because the reaction involves the formation of an ester linkage through the condensation of the carboxylic acid and alcohol.

• Conditions: An acid catalyst is essential to protonate the carbonyl oxygen of the carboxylic acid, making it more susceptible to nucleophilic attack.
• Formation: The reaction results in the release of water, a typical condensation reaction, enhancing the formation of the ester linkage.
• Mistakes to Avoid: Using a base will not facilitate this reaction; rather, it deprotonates the acid, thereby halting ester formation.

In summary, esterification is accurately carried out in an acidic medium rather than a basic one, crucial for understanding reactions in organic chemistry.

Diazomethane Chemistry

Diazomethane \(\mathrm{CH_2N_2}\) is an organic compound known for its role as a methylating agent. Its high reactivity is due to the presence of both a lone electron pair on nitrogen and a highly strained cyclic structure, making it efficient in transferring methyl groups.

Use in Methylation: Diazomethane reacts with carboxylic acids to form esters in processes like converting benzoic acid into methyl benzoate.

Mechanism: It involves nucleophilic attack on the carbonyl carbon, followed by nitrogen gas elimination, resulting in the formation of the ester.

Diazomethane is less commonly used due to safety concerns, as it is toxic and explosive, yet remains valuable for certain chemical transformations.

Hydrolysis of Esters

Hydrolysis is the breakdown of esters \(\mathrm{RCOOR'}\) into carboxylic acids and alcohols, typically facilitated by water or an aqueous medium. Esters are more prone to hydrolysis than amides due to their reactive carbonyl carbon.

• Reactivity Factors: The oxygen in the ester link makes the carbonyl carbon more electrophilic, susceptible to nucleophilic attack, which is essential in hydrolysis.
• Acid or Base Catalysis: Acidic or basic conditions can enhance hydrolysis. In acidic conditions, the ester can be protonated, increasing the susceptibility to nucleophilic water. In a base, an alkali may further speed up the hydrolysis via saponification.
• Comparison with Amides: Acid amides, due to the electron-withdrawing nitrogen, hydrolyze at a slower rate than esters.

Understanding these mechanisms provides insight into selecting conditions for optimal hydrolysis as part of organic synthesis.