Problem 88 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

An organic compound 'A' on treatment with ethyl alcohol gives a carboxylic acid ' \(\mathrm{B}\) ' and compound ' \(\mathrm{C}\) '. Hydrolysis of ' \(\mathrm{C}\) ' under acidic conditions gives 'B' and 'D'. Oxidation of ' \(\mathrm{D}\) ' with \(\mathrm{KMnO}_{4}\) also gives ' \(\mathrm{B}^{\prime}\). ' \(\mathrm{B}\) ' on heating with \(\mathrm{Ca}(\mathrm{OH})_{2}\) gives ' \(\mathrm{E}\) ' (molecular formula, \(\left.\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\right) .^{\text {' } \mathrm{E}}\) ' does not give Tollen's test and does not reduce Fehling's solution but forms a 2,4 dinitrophenylhydrazone. Identify ' \(\mathrm{A}^{\prime},{ }^{\text {' }} \mathrm{B}^{\prime}\), ' \(\mathrm{C}^{\prime}\), ' \(\mathrm{D}\) ' and ' \(\mathrm{E}\) '.

Step-by-Step Solution

Answer

A is ethyl acetate, B is acetic acid, C is ethyl acetate, D is ethanol, and E is acetone.

Step 1: Analyzing Reaction of A with Ethyl Alcohol

The compound 'A' reacts with ethyl alcohol to form a carboxylic acid 'B' and another compound 'C'. This suggests that 'A' is likely an ester since esters commonly react with alcohols in transesterification reactions, producing a new ester and an alcohol.

Step 2: Identifying Compounds From Hydrolysis

The compound 'C' undergoes hydrolysis under acidic conditions to give 'B' and 'D'. This implies that 'C' is an ester, which on hydrolysis yields the carboxylic acid 'B' and an alcohol/formaldehyde 'D'. Given that 'B' is a carboxylic acid and 'D' can be an alcohol, 'C' could be ethyl acetate or similar.

Step 3: Oxidation of D with KMnO4

The alcohol 'D' is oxidized to produce the carboxylic acid 'B'. This implies that 'D' must be a primary alcohol, as primary alcohols are typically oxidized to carboxylic acids. Thus, 'D' could be ethanol, implying that 'B' could be acetic acid.

Step 4: Analyzing the Thermal Decomposition of B

Upon heating 'B' with calcium hydroxide, compound 'E' is obtained. The molecular formula of 'E' is given as \(C_3H_6O\). 'E' does not give Tollen's test or reduce Fehling's solution but does form a 2,4-dinitrophenylhydrazone, suggesting it is a ketone. Likely, 'E' is acetone.

Step 5: Identifying A, B, C, D, and E

Based on the information and deductions: - 'A' is ethyl acetate (an ester). - 'B' is acetic acid (the carboxylic acid formed). - 'C' is ethyl acetate (formed during the process). - 'D' is ethanol (the alcohol product from hydrolysis). - 'E' is acetone (a ketone forming a dinitrophenylhydrazone).

Key Concepts

Esterification

Esterification is a chemical reaction that forms an ester as the main product. Esters are typically formed by the reaction between a carboxylic acid and an alcohol. In the given exercise, compound 'A' is an ester formed through esterification and later participates in a reaction with ethyl alcohol. This transformative process indicates that esterification allows one functional group to be replaced by another under specific conditions, usually in the presence of an acid catalyst.

- Esters are characterized by their distinctive sweet smell and are commonly used in the fragrance and flavor industry.
- This type of reaction is reversible, known as hydrolysis, where the ester can be broken back into the alcohol and carboxylic acid.

Esterification involves the release of water as a by-product, which is why it's crucial to control reaction conditions to prevent the reverse reaction.

Carboxylic Acid

Carboxylic acids are organic compounds containing the carboxyl group (-COOH). In the exercise, 'B' is identified as a carboxylic acid, specifically acetic acid, as it is formed when 'A' reacts with ethyl alcohol. Carboxylic acids are generally acidic in nature and can donate a hydrogen ion in reactions.

- They are soluble in water and often have a sour taste.
- Carboxylic acids play a crucial role as building blocks in organic synthesis and biological processes.

The behavior of carboxylic acids in reactions heavily influences the formation of other compounds, such as esters in esterification or other derivatives when subject to oxidation or reduction reactions.

Transesterification

Transesterification is a process where one ester is transformed into another ester through the exchange of the alkoxy group. The compound 'A' interacting with ethyl alcohol to form 'B' and 'C' is an example of transesterification. This is a common reaction used in biodiesel production and in altering esters for various industrial applications.

- The mechanism involves breaking the existing ester bond and forming new ester bonds.
- Catalysts such as acids or bases are usually used to speed up this process.

Transesterification showcases the versatility of esters in reaction chemistry, allowing the release or consumption of alcohols and acids to create new ester compounds.

Oxidation Reactions

Oxidation reactions involve the loss of electrons or the increase in oxidation state by a molecule. In organic chemistry, these reactions often involve the removal of hydrogen or the addition of oxygen. In the exercise, 'D', an alcohol, is oxidized to 'B', a carboxylic acid. This is typical, as primary alcohols easily oxidize to carboxylic acids in the presence of strong oxidizing agents like \( ext{KMnO}_4\).

- Oxidation is a crucial step in converting primary alcohols to carboxylic acids.
- The use of specific reagents determines the extent and selectivity of oxidation.

Understanding oxidation reactions is vital for predicting product formation paths in complex organic synthesis, such as those described in the exercise where different organic compounds react to form new products.