Question

Which alkane is produced when sodium salt of butanoic acid is heated with soda lime? (a) \(\mathrm{CH}_{3} \mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{4}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\)

Short answer

When sodium salt of butanoic acid is heated with soda lime, the alkane produced is propane (d), which is molecular formula d.

Step-by-step solution

- Understanding the Decarboxylation Reaction

A decarboxylation reaction refers to the chemical reaction where a carboxyl group is removed from a molecule, releasing carbon dioxide. When a carboxylic acid salt is heated with soda lime (a mixture of NaOH and CaO), the salt gets decarboxylated to form the corresponding alkane. The number of carbon atoms in the alkane is one less than that in the carboxylic acid salt, as the carboxyl group (COOH) is lost in the form of carbon dioxide (CO₂).

- Identify the Acid and the Expected Alkane

Given the sodium salt of butanoic acid, the butanoic acid part of the molecule has four carbon atoms. When heated with soda lime, one carbon atom will be lost as carbon dioxide, resulting in the formation of an alkane with three carbon atoms.

- Determine the Structure of the Produced Alkane

An alkane with three carbon atoms is propane. Its molecular formula is d (CH_3CH_2CH_3). Therefore, the correct option for the alkane produced from the decarboxylation of sodium butanoate is propane.

Key concepts

Soda Lime Decarboxylation

When we talk about soda lime decarbxoylation, we're exploring a fascinating and essential reaction in organic chemistry. This reaction is a straightforward and practical way to convert carboxylic acids into alkanes.

Soda lime, a mixture of sodium hydroxide (NaOH) and calcium oxide (CaO), enables this transformation by stripping away the carboxylic group (-COOH) from the acid. When the sodium salt of a carboxylic acid is heated with soda lime, it releases carbon dioxide (CO₂) and forms the corresponding alkane. This process, known as decarboxylation, simplifies complex organic molecules and is a crucial step in various synthetic pathways.

Key Points in Soda Lime Decarboxylation:

• It involves heating a carboxylic acid salt with soda lime.
• A carboxyl group is removed, and CO₂ is released.
• The resultant molecule is an alkane with one less carbon atom than the original acid.

Understanding this reaction is central to grasping how carboxylic acids are converted into simpler hydrocarbons, pivotal in both biological processes and industrial applications.

Butanoic Acid

Butanoic acid sits at the heart of the given exercise, a compound with a four-carbon chain structure, symbolized as C4H8O2. Its distinctive feature is the presence of the carboxylic group. Students often recognize this acid by its unpleasant, rancid smell, common to rancid butter.

As an organic acid, butanoic acid holds importance in various biological functions and is also used in manufacturing processes. Its structure consists of a four-carbon chain with a carboxyl (-COOH) group attached to the end. The chemical formula is often written as CH₃CH₂CH₂COOH, showcasing the methyl (CH₃-) and propyl (CH₂CH₂CH₂-) groups. In its salt form, which is usually combined with sodium or potassium, it becomes a key player in the decarboxylation processes.

Notable Details of Butanoic Acid:

• It consists of a chain of four carbon atoms.
• Known for its strong, unpleasant odor.
• Functional carboxyl group at the end of its structure.

Understanding butanoic acid's structure and properties allows us to predict its behaviors and reactions, like in the decarboxylation with soda lime.

Alkane Formation

Alkane formation is the crux of the decarboxylation reaction discussed in the exercise. Alkanes are the simplest form of hydrocarbons with a single bond between carbon atoms, and they follow the general formula CnH2n+2.

When a carboxylic acid, or its salt, undergoes decarboxylation, an alkane emerges with one less carbon atom than the original acid. This loss of the carboxyl group as CO₂ isn't just a subtraction; it's a transformation resulting in a saturated hydrocarbon - the alkane. In our context, heating butanoic acid's sodium salt with soda lime will lead to the formation of propane, an alkane with three carbon atoms (C₃H₈).

Highlights of Alkane Formation:

• Alkanes have a saturated structure with single bonds only.
• The general formula for alkanes is CnH2n+2.
• Decarboxylation leads to the formation of a shorter-chain alkane.

Through the lens of alkane formation, we can appreciate the elegance of chemical reactions that convert complex structures into simpler, more stable ones, mirroring the process seen in the reaction of butanoic acid's sodium salt with soda lime.