Question

Identify \(\mathrm{R}\) and \(\mathrm{R}^{\prime}\) in Equation 1 when the ester, aspirin, is made from salicylic acid and acetic acid.

Short answer

In the aspirin molecule, the R group is the aromatic ring with a hydroxyl group (\(-OH\)) and a carboxylic acid group (\(-COOH\)) derived from salicylic acid, and the R' group is the methyl group (\(-CH_3\)) derived from acetic acid.

Step-by-step solution

Write the chemical structures of aspirin, salicylic acid, and acetic acid

Aspirin, also known as acetylsalicylic acid, has the chemical structure: \[C_9H_8O_4\] Its structure is shown below: \[ \text{Aspirin:} \hspace{2mm} \text{(R-CO-O-R')} \] ``` O || C | O | C / \ O C | | HOOC-C || OH ``` Salicylic acid has the structure: \[C_7H_6O_3\] Its structure is shown below: \[ \text{Salicylic acid: (R)} \] ``` O || C / \ O C | | HOOC-C || OH ``` Acetic acid has the structure: \[C_2H_4O_2\] Its structure is shown below: \[ \text{Acetic acid: (R')} \] ``` O || C | C | H ```

Identify R and R' groups

Now we will compare the structures of aspirin, salicylic acid, and acetic acid to identify the R and R' groups in the aspirin molecule. - R group (from salicylic acid): The R group in aspirin is the portion derived from salicylic acid. The unique part of the salicylic acid molecule that is not present in acetic acid is the aromatic ring with a hydroxyl group (\(-OH\)) and a carboxylic acid group (\(-COOH\)). Thus, the R group in aspirin is: ``` O || C / \ O C | | HOOC-C || OH ``` - R' group (from acetic acid): The R' group in aspirin is the portion derived from acetic acid. The R' group in this case is simply a methyl group, \(-CH_3\). Thus, the R' group in aspirin is: ``` -CH_3 ``` So, the R group is the aromatic ring with a hydroxyl group (\(-OH\)) and a carboxylic acid group (\(-COOH\)) derived from salicylic acid, and the R' group is the methyl group (\(-CH_3\)) derived from acetic acid.

Key concepts

Chemical Structures

Understanding the chemical structures of molecules is crucial for grasping how chemical reactions occur. Each substance involved in the synthesis of aspirin is represented by a unique chemical structure. For salicylic acid and acetic acid, their structures determine the functional groups that interact during the esterification process to form aspirin.

Aspirin's molecular formula is \( C_9H_8O_4 \) and consists of a benzene ring (an aromatic ring), a carboxylic acid group (–COOH), and an ester group (–COO–). The 'R' and 'R'' groups highlighted in the synthesis of aspirin represent distinct parts of the reactant molecules transformed in the creation of the ester linkage.

Recognizing the visual representation of these molecules and their groups is essential. While molecules like acetic acid have a relatively simple structure, salicylic acid includes a benzene ring, which is typical for aromatic compounds.

Salicylic Acid

Salicylic acid, with the formula \( C_7H_6O_3 \), plays a significant role in the synthesis of aspirin. It’s the source of the 'R' group in the aspirin molecule and provides the structure necessary for the esterification reaction. Salicylic acid contains both a hydroxyl group (\(-OH\)) and a carboxylic acid group (\(-COOH\)), making it a critical compound in the production of many pharmaceuticals.

Salicylic acid itself has important properties. It is known for its usage in acne treatments and other skin products. Understanding the role of its chemical structure helps to see how it interacts with acetic acid to produce aspirin.

Acetic Acid

Acetic acid (\( C_2H_4O_2 \) or also known as ethanoic acid) is the component from which the 'R'' group in aspirin is derived. It’s a simple molecule consisting of a methyl group attached to a carboxyl group. In the context of aspirin synthesis, acetic acid provides the acetyl group (\(-COCH_3\)) that is transferred to the salicylic acid to form the acetylsalicylic acid.

Although it's a simple molecule, acetic acid is a fundamental chemical reagent used widely in the chemical industry. Its ability to donate an acetyl group is exploited in many different chemical reactions beyond aspirin synthesis, including the production of polymers and other chemicals.

Esterification

Esterification is a chemical reaction in which an alcohol and a carboxylic acid combine to form an ester. In the case of aspirin synthesis, salicylic acid (the alcohol component) reacts with acetic acid (the carboxylic acid component) to form acetylsalicylic acid. This specific esterification is a critical step in creating aspirin and involves the transfer of the acetyl group from acetic acid to the hydroxyl group of salicylic acid.

In simpler terms, during the reaction, the \(-OH\) part of the acid reacts with the \(-H\) part of the alcohol, releasing a molecule of water (\(H_2O\)) and forming an ester bond. The ester bond in aspirin is what gives it its pain-relieving and anti-inflammatory properties. Understanding this reaction is fundamental for students studying organic chemistry, as it is a classic example of how small organic molecules interact to form more complex ones.