Question

Each question in this section has four suggested answers of which ONE OR MORE answers will be correct. \(\mathrm{CH}_{3} \mathrm{COOH} \underset{\text { (ii) heat }}{\stackrel{(\mathrm{i}) \mathrm{Ca}(\mathrm{OH})_{2}}{\longrightarrow}}(\mathrm{P})\) The organic compound (P) formed in the above reaction (a) does not reduce Tollens' reagent (b) does not undergo aldol condensation (c) reacts with chloroform in presence of alkali (d) gives two geometrical isomers of the oxime when treated with hydroxylamine

Short answer

(a) P does not reduce Tollens' reagent (b) P does not undergo aldol condensation (c) P reacts with chloroform in the presence of alkali (d) P gives two geometrical isomers of the oxime when treated with hydroxylamine Answer: (a) and (b) are correct statements. Explanation: When acetic acid reacts with calcium hydroxide, it forms a calcium salt, which upon heating undergoes decarboxylation to form methane (CH4) as the organic compound (P). Methane is an alkane and does not reduce Tollens' reagent or undergo aldol condensation. It does not react with chloroform in the presence of alkali (Reimer-Tiemann reaction) and does not give geometrical isomers with oxime formation due to the presence of single bonds only.

Step-by-step solution

Identify the reaction of acetic acid with calcium hydroxide

First, we need to recognize that acetic acid (CH3COOH) is a carboxylic acid and calcium hydroxide (Ca(OH)2) is a strong base. When a carboxylic acid reacts with a strong base, a salt is formed by the acid-base reaction: $$\mathrm{CH}_{3} \mathrm{COOH} + \mathrm{Ca}(\mathrm{OH})_{2} \longrightarrow \mathrm{CH}_{3} \mathrm{COO}^{-}\mathrm{Ca}^{2+} + 2\mathrm{H}_{2}\mathrm{O}$$

Identify the compound formed by heating the salt

Now that we have formed a salt, we will consider the effect of heating the salt. When the calcium salt of a carboxylic acid is heated, it undergoes a decarboxylation reaction, which results in the formation of an organic compound: $$\mathrm{CH}_{3} \mathrm{COO}^{-}\mathrm{Ca}^{2+} \xrightarrow{\text{heat}} \mathrm{CH}_{4} + \mathrm{CaCO}_{2}$$ The organic compound (P) formed here is methane (CH4).

Analyze the properties of methane

With the formation of methane as the product (P), we can now investigate its properties and determine the validity of statements (a), (b), (c), and (d): (a) Methane does not reduce Tollens' reagent - Correct. Tollens' reagent (a silver nitrate solution with ammonia) is used to differentiate between aldehydes and ketones. However, methane is an alkane, and it will not react with Tollens' reagent. (b) Methane does not undergo aldol condensation - Correct. Aldol condensation is a reaction that occurs between two molecules of aldehydes or ketones. Again, methane is an alkane, so it won't react in aldol condensation. (c) Methane reacts with chloroform in the presence of alkali - Incorrect. This reaction is called the Reimer-Tiemann reaction, and it occurs with phenols. Methane is an alkane and will not undergo this reaction. (d) Methane gives two geometrical isomers of the oxime when treated with hydroxylamine - Incorrect. Geometrical isomers result from the presence of a double bond or a ring structure in the molecule. Methane is an alkane with only single bonds and will not exhibit geometrical isomerism. Based on the properties of methane, the correct statements are (a) and (b).

Key concepts

Carboxylic Acid and Strong Base Reaction

Understanding the interaction between carboxylic acids and strong bases is fundamental in organic chemistry. A carboxylic acid such as acetic acid \reaction:
)\(CH_3COOH\) ), when it reacts with a strong base like calcium hydroxide \reaction:
)\(Ca(OH)_2\) ), the acid donates a proton (H+) to the base. This neutralization process forms a salt (in this case, calcium acetate \(CH_3COO^-Ca^{2+}\)) and water \reaction:
)\(2H_2O\) ). This type of reaction showcases the acidic properties of the carboxylic acid group and its ability to form salts with metals, which is pivotal in various industrial and biochemical processes.

Properties of Methane

Methane \reaction:
)\(CH_4\) ) is the simplest alkane and is a major component of natural gas. It is colorless, odorless when pure, and lighter than air. Its tetrahedral structure with four single covalent bonds makes it a non-polar molecule. Methane is notably unreactive due to the high strength of its C-H bonds, and it does not engage in reactions such as reduction, aldol condensation, or formation of geometrical isomers. In the context of environmental science, methane is also known as a potent greenhouse gas with implications for climate change. Its physical and chemical properties are integral to understanding various chemical reactions and environmental issues.

Tollens' Reagent Reaction

Tollens' reagent, which is a solution of silver nitrate in ammonia, is used in a classic test for the presence of aldehyde functional groups in a compound. When an aldehyde is present, it gets oxidized, and the Tollens' reagent is reduced, leading to the deposition of metallic silver and the formation of a characteristic 'silver mirror' on the test tube. Importantly, Tollens' reagent does not react with alkanes like methane because they lack the necessary functional group for the reaction. This selective reactivity is what makes Tollens' test a valuable tool for distinguishing aldehydes from other types of organic compounds.

Aldol Condensation

Aldol condensation is a powerful reaction that creates carbon-carbon bonds, allowing the synthesis of complex molecules from simpler components. It occurs between two aldehyde or ketone molecules in the presence of a base. The process involves the formation of an aldol through the base-catalyzed reaction of an enol or enolate ion with a carbonyl group. The aldol product can then undergo dehydration to yield an α,β-unsaturated carbonyl compound. This reaction is widely employed in organic synthesis to create a vast diversity of compounds. It is important to remember that aldol condensation requires the reactant molecules to have at least one α-hydrogen atom, which alkanes like methane do not possess, hence methane does not participate in this type of reaction.