Problem 51 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write a balanced chemical equation using condensed structural formulas for the saponification (base hydrolysis) of (a) methyl propionate, \((\mathbf{b})\) phenyl acetate.

Step-by-Step Solution

Answer

The balanced chemical equations for the saponification of (a) methyl propionate and (b) phenyl acetate are: a) \(CH_3CH_2COOCH_3 + NaOH \rightarrow CH_3CH_2COONa + CH_3OH\) b) \(C_6H_5COOCH_3 + NaOH \rightarrow C_6H_5COONa + CH_3OH\)

Step 1: a) Saponification of methyl propionate

Step 1: Identify the reactants Methyl propionate is an ester with the condensed structural formula CH_3CH_2COOCH_3. The base used in saponification is usually a hydroxide ion (OH^⁻). In this case, let's use sodium hydroxide (NaOH) as the base. Step 2: Write the unbalanced equation Now, we can write the unbalanced equation: CH_3CH_2COOCH_3 + NaOH Step 3: Identify the products The products of the saponification are an alcohol (formed by adding H from the OH^⁻ to the CH_3) and a carboxylate salt (formed by adding the O^⁻ from the OH^⁻ to the ester group). The products are methanol (CH_3OH) and sodium propionate (CH_3CH_2COONa). Step 4: Write the balanced equation The balanced equation for the saponification of methyl propionate is: \[CH_3CH_2COOCH_3 + NaOH \rightarrow CH_3CH_2COONa + CH_3OH\]

Step 2: b) Saponification of phenyl acetate

Step 1: Identify the reactants Phenyl acetate is an ester with the condensed structural formula C_6H_5COOCH_3. Again, let's use sodium hydroxide (NaOH) as the base. Step 2: Write the unbalanced equation Now, we can write the unbalanced equation: C_6H_5COOCH_3 + NaOH Step 3: Identify the products The products of the saponification are an alcohol (formed by adding H from the OH^⁻ to the CH_3) and a carboxylate salt (formed by adding the O^⁻ from the OH^⁻ to the ester group). The products are methanol (CH_3OH) and sodium phenylacetate (C_6H_5COONa). Step 4: Write the balanced equation The balanced equation for the saponification of phenyl acetate is: \[C_6H_5COOCH_3 + NaOH \rightarrow C_6H_5COONa + CH_3OH\]

Key Concepts

Chemical Equations

In chemistry, a chemical equation represents a chemical reaction, using symbols and formulas to depict the reactants and products. Saponification is a type of chemical reaction where an ester is hydrolyzed by a base, typically resulting in an alcohol and a salt.
This involves not just identifying the reactants and products but also ensuring the equation is balanced. A balanced chemical equation has equal numbers of each type of atom on both sides of the equation.
Writing a balanced equation involves:

• Identifying the reactants and products
• Using chemical formulas for each compound
• Ensuring that the same number of each type of atom appears on both sides

This approach not only represents the process better but also respects the Law of Conservation of Mass, ensuring no atoms are lost or gained throughout the reaction.

Methyl Propionate

Methyl propionate is an organic compound that falls under the category of esters. It has the structural formula of CH₃CH₂COOCH₃, representing a molecule comprised of a propionyl group (CH₃CH₂COO−) attached to a methoxy group (CH₃O−).
In the saponification process, methyl propionate reacts with a base, such as sodium hydroxide (NaOH). The hydroxide ion (OH⁻) attacks the carbon in the ester group, leading to the formation of methanol (CH₃OH) and sodium propionate (CH₃CH₂COONa).
This reaction can be summarized by the balanced chemical equation:\[CH₃CH₂COOCH₃ + NaOH \rightarrow CH₃CH₂COONa + CH₃OH\]This equation shows the conversion of the ester into an alcohol and a carboxylate salt, illustrating the fundamentals of saponification in a realistic context.

Phenyl Acetate

Phenyl acetate is another ester showcased in saponification exercises. This compound is represented by the formula C₆H₅COOCH₃, where a phenyl group (C₆H₅−) is bonded to an acetyl group (CH₃CO−), connected by an ester linkage.
During saponification with a base like sodium hydroxide (NaOH), the NaOH dissociates to provide hydroxide ions (OH⁻). These ions interact with phenyl acetate, transforming it into methanol (CH₃OH) and sodium phenylacetate (C₆H₅COONa).
The process can be captured in the balanced chemical equation:\[C₆H₅COOCH₃ + NaOH \rightarrow C₆H₅COONa + CH₃OH\]Like methyl propionate, phenyl acetate undergoes a similar chemical change, emphasizing the role of esters in organic chemistry reactions and the fundamentals that govern these transformations.

Organic Chemistry

Organic chemistry is a branch of chemistry focused on carbon-containing compounds, including both simple molecules and complex polymers. Ester saponification is a core reaction in organic chemistry, illustrating how organic compounds interact with bases to yield new products.
In the context of saponification, esters such as methyl propionate and phenyl acetate react with hydroxide ions to form alcohols and salts.
This reaction involves:

• The cleavage of the ester bond by the base
• The formation of an alcohol and a carboxylate salt as final products

Understanding these reactions aids in grasping broader organic chemistry principles, such as reactivity, molecular structure, and the nature of chemical transformations. It highlights the versatility of carbon compounds and their significant roles in both biological and industrial processes.