Problem 121 - Chemistry The Molecular Nature of Matter

Question

Write the structures of the products that form in each of the following situations. If no reaction occurs, write "no reaction." (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2}^{-}+\mathrm{HCl}(a q) \longrightarrow\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{3}+\mathrm{H}_{2} \mathrm{O} \stackrel{\text { heat }}{\longrightarrow}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}+\mathrm{NaOH}(a q) \longrightarrow\)

Step-by-Step Solution

Answer

The products are: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2}H\), (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2}H\) and \(\mathrm{CH}_{3}OH\), (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2}Na\) and \(\mathrm{H}_{2}O\).

Step 1: Analyzing the first reaction

The first reaction involves a carboxylate ion, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2}^{-}\), reacting with hydrochloric acid \(\mathrm{HCl}\). Carboxylate ions can react with acids to form carboxylic acids. The \(\mathrm{HCl}\) will donate a proton to the carboxylate ion, resulting in the formation of propanoic acid. The product is \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2}H\).

Step 2: Analyzing the second reaction

The second reaction involves the heating of an ester \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{3}\) with water. This is a typical ester hydrolysis reaction under acidic conditions which leads to the formation of the corresponding carboxylic acid and alcohol. However, since no acid catalyst is provided, the reaction under heat may lead to the formation of a carboxylic acid and an alcohol. The products are propanoic acid \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2}H\) and methanol \(\mathrm{CH}_{3}OH\).

Step 3: Analyzing the third reaction

The third reaction involves a carboxylic acid \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} H\) reacting with sodium hydroxide \(\mathrm{NaOH}\). This is a neutralization reaction where the acid reacts with the base to form a salt and water. The product of this reaction is the sodium salt of the carboxylic acid, sodium butanoate \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2}Na\), and water \(\mathrm{H}_{2}O\).

Key Concepts

Ester Hydrolysis

Ester hydrolysis is a chemical reaction where an ester is broken down into a carboxylic acid and an alcohol. This reaction is particularly important in organic chemistry and biochemistry because esters are commonly found in fats, oils, and various biological molecules.

In our example, the ester ( (03CH2cyc 03CH3 + 03H2nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn (heat) ) nn nnnnnnn was heated with water without an acid catalyst present, leading to its breakdown into propanoic acid ( nnnnnnnnnnnnnnn ( nnn nnn Hnnnnnn nnn nnnnnnnnn nnnnnnnn nnn nnnnnnnnnnnnnnn ( ) nnnnnnnnnnn nnnnnnn nn nnn nnnnnnnnnnnnnnnn nnn ( ) nnnnnnnnnnnnnnnnnn ( nnnnnnn ( ( n nnnnnnnnnnnnnnn nnnnnnn nnnnnnnnnnnnnnn nnnnnnnnn nnnnn nnnnnnn ( nn nnnnnnn n nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn ( nnnnnnnnnnnnnnnn nnnnnnn nnnnnnnnnnn nnnnnnn nnnnnnnnnnnnnnnnnnn nnnnnnn nnnnnnn nnnnnnn nnnnnnn nnnnnnn ( nnnnn nnnnn nnnnn nnnnnnnnn nnnnnnnnnnnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnn nnnnnnnnnnnnnnnn CO2H) and methanol (CH3OH). While ester hydrolysis typically requires a catalyst to speed up the reaction, heat can also drive the reaction; however, the absence of the catalyst makes the process much slower.

Undergraduate students studying organic chemistry should understand the effects of different conditions on ester hydrolysis, such as the presence or absence of an acid or base, as they can significantly impact the rate and outcome of the reaction.

Carboxylate Ion Reactivity

The carboxylate ion—often depicted as RCO2- where R is a hydrocarbon group—is known for its high reactivity due to its negative charge. The presence of this negative charge makes it a good nucleophile, meaning it can readily donate a pair of electrons to an electrophile, such as a proton.

In the given exercise, the carboxylate ion 03CH2CH2 CO2-reacts with hydrochloric acid (HCl) in an aqueous solution. This is a typical reaction where the acidic proton from HCl is attracted to the negative charge on the carboxylate ion, resulting in the formation of propanoic acid 03CH2 CH2 CO2H. By capturing a proton (H+), the carboxylate ion is neutralized to form a carboxylic acid.

Understanding the reactivity of carboxylate ions is crucial for students because it enables them to predict the course of reactions involving carboxylic acid derivatives, which are common in biochemical processes and organic synthesis.

Neutralization Reaction

A neutralization reaction is a type of chemical reaction in which an acid and a base react to form a salt and water. This is one of the fundamental reactions in chemistry that exemplifies the concept of acid-base chemistry.

In our example, propanoic acid 03CH2CH2CH2nnnnnnnnnnnn CO2H nnnnn nnnnnnnnnnn nnnnnnnn nnnnnnn nnnnnnnnnnnnnnnnnn nnnnnnn nnnnnnn nnnn reacts with sodium hydroxide (NaOH), which is a basic compound. The reaction yields water (nnnnnnnnnnnn ( 2O) nnnnnnnnnnnnnnnn nnnnn nnnnnn nnnnn nnnnnnnnnnn nnnnnnnnn nnnnnnnnnnnnn nnnnnnnnnnnnnn nnnnnnn nnnnnnn nnnnnnnnnnnnnnn nnn nnn nnn nnnnnnn nnnnnnn nnnnnnn nnnnnnn nnnnnnn nnnnnnn nnnnnnn nnnnnnn ) and the sodium salt of the carboxylic acid, sodium butanoate 03CH2CH2CH2CO2Na.

Students should recognize the pattern of neutralization reactions, as these reactions are critical in various applications such as titrations in analytical chemistry, pharmaceutical formulations, and everyday household products. Being well-versed in these reactions can help in understanding the balance of pH in different environments and systems.