Question

During formation of aspirin from salicylic acid by reaction of ${\left({\mathrm{CH}}_3\mathrm{CO}\right)}_2\mathrm{O}/{\mathrm{H}}^{+}$, which functional group remains unaffected? (A) Carboxylic acid (B) Phenolic group (C) Acid anhydride (D) Ester

Short answer

The functional group that remains unaffected during the formation of aspirin from salicylic acid is the phenolic group. The correct answer is (B) Phenolic group.

Step-by-step solution

Determine the reactants

We are given salicylic acid and ${\left({\mathrm{CH}}_3\mathrm{CO}\right)}_2\mathrm{O}/{\mathrm{H}}^{+}$. The structure of salicylic acid is given by the formula ${\mathrm{C}}_7{\mathrm{H}}_6{\mathrm{O}}_3$ and contains a carboxylic acid group and a phenolic group.

Examine the product of the reaction (aspirin)

Aspirin is formed during this reaction, its structural formula is ${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$. Aspirin contains an ester group, which results from the reaction between the carboxylic acid group of salicylic acid and ${\left({\mathrm{CH}}_3\mathrm{CO}\right)}_2\mathrm{O}/{\mathrm{H}}^{+}$.

Analyze each given option to find the unaffected functional group

(A) Carboxylic acid: This group reacts with ${\left({\mathrm{CH}}_3\mathrm{CO}\right)}_2\mathrm{O}/{\mathrm{H}}^{+}$ to form the ester group in aspirin. So, it is affected during the reaction. (B) Phenolic group: This group does not react in forming aspirin and remains intact in the final product. So, the phenolic group is unaffected during the reaction. (C) Acid anhydride: This group is not present in either the reactants or the product, so it is irrelevant to the reaction. (D) Ester: This group is formed as a result of the reaction between the carboxylic acid group of salicylic acid and ${\left({\mathrm{CH}}_3\mathrm{CO}\right)}_2\mathrm{O}/{\mathrm{H}}^{+}$. So, it is affected during the reaction. Thus, the functional group that remains unaffected during the formation of aspirin from salicylic acid is the phenolic group. The correct answer is (B) Phenolic group.

Key concepts

Functional Groups

In organic chemistry, a functional group refers to specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.
Each functional group behaves consistently from one molecule to another, enabling chemists to predict the behavior and reactions of these molecules.
This concept is essential for identifying the chemical properties and reactivity of a compound.Functional groups are the cornerstone of organic chemistry classifications, as they determine the structure and reactivity of organic molecules. For example:

• The carboxylic acid group \( (-COOH) \) is notable for being acidic and forming esters when reacting with alcohols.
• The phenolic group \( (-OH) \) when attached to an aromatic ring is generally less reactive than typical alcohols due to resonance stabilization.
• An ester group \( (-COOR) \) results from the reaction between an acid and an alcohol, and is known for its distinctive smells and uses in fragrances and flavorings.

Understanding functional groups simplifies the study of organic chemistry by categorizing substances into families with similar reactivities and properties.

Esterification

Esterification is a crucial organic chemistry reaction that involves the formation of an ester from an acid and an alcohol.
In this process, an alcohol reacts with a carboxylic acid in the presence of an acid catalyst, usually resulting in the formation of an ester and water.In the formation of aspirin, esterification plays a significant role. The reaction involves the carboxylic acid group of salicylic acid and acetic anhydride (or acetic acid under acidic conditions) to produce aspirin, which contains an ester linkage.The general reaction for esterification is:$$RCOOH+R^{\prime }OH\to RCOO{R}^{\prime }+H_{2}O$$

• Here, \( RCOOH \) represents the carboxylic acid, $R^{\prime }OH$ is the alcohol, $RCOO{R}^{\prime }$ is the ester, and $H_{2}O$ is water.

Esterification is a reversible reaction and can be driven to completion by removing the produced water or using excess reactants. It is widely used in industries for making fragrances, plastics, and pharmaceuticals.

Phenolic Group

The phenolic group is a type of functional group characterized by an -OH group bonded to an aromatic hydrocarbon.
This group is significant due to its unique properties, which differ from typical alcohols. Because of the aromatic's ring resonance, phenolic groups are less reactive compared to aliphatic alcohols. In the formation of aspirin from salicylic acid, the phenolic group remains unaffected.
The reaction specifically targets the carboxylic acid group, transforming it into an ester, while the phenolic group retains its original structure. Characteristics of the phenolic group include:

• Lower reactivity: The stability provided by the aromatic ring makes phenols less prone to oxidation compared to other alcohols.
• Distinct acidity: Phenols are more acidic than typical alcohols due to resonance stabilization.
• Usage in synthesis: Compounds containing phenolic groups often serve as antioxidants, antiseptics, and precursors to significant materials like epoxy resins.

Understanding the reactivity and stability of phenolic groups is vital in organic synthesis and drug development.