Question

Each question in this section has four suggested answers out of which ONE OR MORE answers will be correct. Kolbe's electrolytic synthesis gives hydrocarbons with (a) sodium succinate (b) potassium maleate (c) sodium acetate (d) malonic acid

Short answer

Answer: (c) Sodium acetate

Step-by-step solution

Understand Kolbe's electrolysis reaction

Kolbe's electrolytic synthesis is a type of organic reaction in which carboxylate ions (RCOO-) are subjected to electrolysis, leading to the formation of the corresponding radical (R.) and ultimately to the formation of hydrocarbons through a coupling reaction (2R. -> R-R). The overall reaction can be represented as: 2 RCOO- -> R-R + 2 CO2 + 2 e-

Analyze each given compound for their possible participation in Kolbe's electrolytic synthesis

(a) Sodium succinate: The molecular formula of sodium succinate is NaOOCCH2CH2COONa. Since the succinate ion's carbon atoms are linked via a single bond, this compound cannot undergo Kolbe's electrolytic synthesis to form hydrocarbons. (b) Potassium maleate: The molecular formula of potassium maleate is KOOCCH=CHCOOK. Since it contains a double bond between the carbon atoms (C=C), this compound is not capable of undergoing Kolbe's electrolytic synthesis for the formation of hydrocarbons. (c) Sodium acetate: The molecular formula of sodium acetate is CH3COONa. Sodium acetate contains a carboxylate group (CH3COO-), which is the necessary requirement for Kolbe's electrolytic synthesis. So, this compound can participate in the Kolbe electrolysis reaction to form hydrocarbons. (d) Malonic acid: The molecular formula of malonic acid is HOOCCH2COOH. Malonic acid contains two carboxylate groups, which have the potential to undergo Kolbe's synthesis reaction; however, the resulting radicals (CH2.) would undergo dimerization to form ethane and carbon dioxide.

Determine the correct answer(s)

Based on our analysis, the only compound that can undergo Kolbe's electrolytic synthesis to produce hydrocarbons is sodium acetate (c). Therefore, the correct answer is: (c) Sodium acetate

Key concepts

Hydrocarbon Synthesis

Hydrocarbon synthesis through Kolbe's Electrolysis is an intriguing process in organic chemistry. It involves transforming carboxylate ions into hydrocarbons. This method is essential because it provides a straightforward mechanism for creating carbon-carbon bonds. Kolbe’s electrolysis facilitates the coupling of radicals to form alkanes.

The reaction kicks off by electrolyzing a carboxylate ion, like sodium acetate (\( \text{CH}_3\text{COO}^- \)), in an aqueous solution. The electric current induces the decarboxylation of the ion, leading to the formation of a methyl radical (\( \text{CH}_3\cdot \)). Then, two methyl radicals couple to form ethane (\( \text{CH}_3\text{CH}_3 \)) as the primary hydrocarbon product. This simple yet ingenious mechanism opens pathways to more complex hydrocarbon structures.

• Uses carboxylate ions and electricity.
• Forms radical intermediates.
• Ends with alkane formation.

Understanding this synthesis helps students appreciate how organic chemistry employs basic principles to build complex molecules.

Carboxylate Ion

A carboxylate ion is an essential component involved in Kolbe's electrolysis. It typically originates from a carboxylic acid by losing a hydrogen ion (proton) from its carboxyl group (\( \text{COOH} \)). This deprotonation process results in the familiar carboxylate ion (\( \text{RCOO}^- \)).

These ions are interesting due to their negative charge, making them reactive participants in electrochemical reactions. In the case of Kolbe's electrolysis, the carboxylate ion is crucial as it undergoes decarboxylation at the anode to form a carbon-centered radical. This radical is the precursor to the hydrocarbon chain formed by coupling with another radical.

• Derived from carboxylic acids.
• Features a negative charge.
• Involves decarboxylation to form radicals.

Learning about carboxylate ions provides insight into how negative charges alter molecular behavior and facilitate unique reaction pathways.

Organic Reaction Mechanism

Organic reaction mechanisms detail the step-by-step transformation occurring during a chemical reaction. In Kolbe's electrolysis, the reaction mechanism starts with the oxidation of the carboxylate ion at the anode. The ion loses a carbon dioxide molecule and an electron, resulting in the formation of a radical.

This newly formed radical is highly reactive, seeking stability by pairing with another radical. The subsequent dimerization, or coupling, reaction leads to the formation of hydrocarbons. This stage is pivotal because each radical represents a carbon atom, and linking them builds the hydrocarbon chains.
Kolbe's electrolysis exemplifies how identifying intermediates and products at each stage helps elucidate the entire process. This understanding is crucial in predicting the outcome of similar organic reactions.

• Involves initial oxidation at the anode.
• Formation of radical intermediates.
• Coupling leads to hydrocarbon production.

Grasping organic reaction mechanisms enriches students' ability to predict and manipulate chemical reactions in synthetic chemistry.