Question

Hydrolysis of an ester gives a carboxylic acid which on Kolbe's electrolysis yields ethane. The ester is (a) Methyl methanoate (b) Methyl propanoate (c) Ethyl methanoate (d) Methyl ethanoate

Short answer

The ester is Methyl ethanoate.

Step-by-step solution

Understand the Problem

The ester is hydrolyzed to give a carboxylic acid which, upon Kolbe’s electrolysis, produces ethane. We need to identify which ester fits this description.

Recall Kolbe's Electrolysis

Kolbe's electrolysis involves the decarboxylation of a carboxylic acid to form alkanes. Specifically, carboxylates are converted to alkanes with one carbon less than the acid.

Determine the Carboxylic Acid

We know the carboxylic acid must have two carbons because Kolbe's electrolysis yields ethane, which has two carbons. Therefore, the carboxylic acid must be ethanoic acid (acetic acid), CH₃COOH.

Match Ester to Carboxylic Acid

The carboxylic acid ethanoic acid is produced by hydrolyzing the ester shown in one of the options. Methyl ethanoate hydrolyzes to ethanoic acid and methanol.

Conclusion

Since the carboxylic acid obtained from hydrolyzing the ester is ethanoic acid, and Kolbe's electrolysis results in ethane, the correct ester is Methyl ethanoate.

Key concepts

Hydrolysis of Esters

Hydrolysis is a fundamental chemical reaction where a compound, often an ester, reacts with water to break down into more basic components. In the context of esters, hydrolysis involves the breakdown of the ester bond, resulting in a carboxylic acid and an alcohol. This process is crucial in organic chemistry due to its multiple applications, including synthesis and degradation.

When an ester like methyl ethanoate undergoes hydrolysis, it reacts with water in the presence of an acid or a base catalyst. If the reaction is acid-catalyzed, it results in an equilibrium state where the ester part converts to a carboxylic acid (ethanoic acid) and an alcohol (methanol).

Hydrolysis is effectively reversing the esterification process. The choice of catalyst can influence the speed and efficiency of this reaction, making the understanding of hydrolysis mechanisms essential for many industrial and laboratory processes.

Decarboxylation

Decarboxylation is the process where a carboxyl group is removed from a molecule, releasing carbon dioxide. This reaction is vital in organic chemistry, particularly when converting carboxylic acids into hydrocarbons.

During Kolbe’s electrolysis, decarboxylation plays a crucial role. The process involves the conversion of carboxylates (salts of carboxylic acids) into alkanes when subjected to electrical current. In this case, the reaction removes the carboxyl group from the ethanoic acid, resulting in the formation of ethane, which is a simple two-carbon alkane.

Decarboxylation is highly relevant not only in laboratory settings but also in metabolic pathways. It also demonstrates how electrical energy can be applied in organic transformations, offering a practical application of electrochemistry in synthesis.

Carboxylic Acids

Carboxylic acids are organic compounds characterized by the presence of at least one carboxyl group (–COOH). They are widely recognized for their acidic properties, which arise from the tendency of the –OH group to donate a proton (H⁺).

In organic reactions, carboxylic acids serve as essential precursors and intermediates. For instance, ethanoic acid (commonly known as acetic acid) is an important carboxylic acid produced via the hydrolysis of methyl ethanoate. Once produced, it can undergo various transformations, including Kolbe's electrolysis to yield ethane.

Understanding the behavior of carboxylic acids, such as their reactivity and how they interact with other compounds, is fundamental for designing and performing chemical syntheses. Their properties make them versatile components in pharmaceuticals, food additives, and industrial chemicals.

Organic Chemistry Reactions

Organic chemistry reactions are at the heart of transforming simple organic molecules into complex structures. The reactions usually involve the making or breaking of chemical bonds in organic molecules. The exploration of these reactions allows chemists to create a vast array of organic compounds.

Kolbe's electrolysis is a noteworthy organic reaction, exemplifying the synthesis of alkanes from carboxylic acids through the application of electric current. Such reactions not only illustrate the fundamental principles of organic chemistry but also showcase their practical applications in synthesizing various organic molecules, including fuels and solvents.

Organic reactions can be categorized into several types, including addition, substitution, elimination, and rearrangement reactions. Each plays a unique role in facilitating the synthesis and modification of organic compounds, making them indispensable tools in the chemist's repertoire. Understanding these reactions is crucial for advancing fields such as materials science, pharmaceuticals, and green chemistry.