Problem 124 - A Complete Resource Book in Chemistry for JEE Main

Question

An organic compound 'A' reacts with methyl magnesium iodide, to form an addition product which on hydrolysis forms the compound 'B'. Compound B' gives blue colour salt in Victor Meyer's test. The compounds 'A' and 'B' are respectively (a) acetaldehyde and isopropyl alcohol (b) acetone and isopropyl alcohol (c) acetaldehyde and tertiary butyl alcohol (d) acetaldehyde and ethyl alcohol

Step-by-Step Solution

Answer

Correct answer is (b) acetone and isopropyl alcohol.

Step 1: Identify the Grignard Reaction

The problem mentions an organic compound 'A' reacting with methyl magnesium iodide. Methyl magnesium iodide is a Grignard reagent, and it typically reacts with carbonyl compounds like aldehydes and ketones to form alcohols after hydrolysis. Therefore, compound 'A' must be either an aldehyde or a ketone.

Step 2: Examine the Hydrolysis Product

The addition product of the reaction of 'A' with methyl magnesium iodide is an alkoxide. Upon hydrolysis, this forms an alcohol 'B'. Thus, we need to determine what alcohol is formed on hydrolysis.

Step 3: Analyze Victor Meyer's Test

Victor Meyer's test is used to differentiate between primary, secondary, and tertiary alcohols based on the color of the salt formed. The blue color indicates that 'B' is a secondary alcohol.

Step 4: Match to Possible Compounds

From the information, if 'B' is a secondary alcohol, it must be isopropyl alcohol. Compound 'A' must therefore be a ketone since the formation of a secondary alcohol from a Grignard reagent usually involves adding the Grignard reagent to a ketone.

Step 5: Conclusion from Options

Looking at the options, if 'B' is isopropyl alcohol, the only matching pair from the choices provided is acetone (a ketone) as 'A' and isopropyl alcohol as 'B', making the correct answer option (b).

Key Concepts

Victor Meyer test

The Victor Meyer test is a classical chemical test used to distinguish between different types of alcohols—primary, secondary, and tertiary. This test is based on the formation of nitroalkanes, which upon further reaction create nitrite salts of different colors.

• Primary alcohols react to form a red colored salt.
• Secondary alcohols produce a blue color in the resulting salt.
• Tertiary alcohols do not form any color.

In the question at hand, compound 'B' was identified as forming a blue color in Victor Meyer's test, indicating that it is a secondary alcohol, namely isopropyl alcohol. This test is a useful tool in organic chemistry for analyzing and confirming the structure of alcohols.

carbonyl compounds

Carbonyl compounds are a group of organic compounds that contain a carbonyl group (C=O). The carbon atom in the carbonyl group is sp² hybridized, making it susceptible to nucleophilic attack due to the partial positive charge. Carbonyl compounds include aldehydes, ketones, carboxylic acids, and esters.

• Aldehydes have a carbonyl group bonded to at least one hydrogen atom.
• Ketones have the carbonyl group bonded to two carbon atoms.

These compounds are essential in many chemical reactions, such as nucleophilic addition reactions. In the given problem, the compound 'A' is identified as a carbonyl compound which was involved in a reaction with a Grignard reagent to form an alcohol. The characteristics of carbonyl compounds make them highly reactive and useful in forming secondary alcohols, as seen with the compound 'B' in this context.

secondary alcohols

Secondary alcohols are a type of alcohol where the hydroxyl group (-OH) is attached to a carbon atom that is bonded to two other carbon atoms. These alcohols are identified based on their molecular structure and reactivity. Secondary alcohols can be distinguished by several properties:

• They generally have a formula \(R^1R^2CHOH\), where \(R^1\) and \(R^2\) are alkyl or aryl groups.
• In the Victor Meyer test, they typically produce a blue color as their unique identifying feature.
• Secondary alcohols are formed in Grignard reactions when a Grignard reagent reacts with a ketone.

In this exercise, the secondary alcohol isopropyl alcohol was formed from the reaction and subsequent hydrolysis involving acetone and a Grignard reagent.

aldehydes and ketones

Aldehydes and ketones are both part of the broader carbonyl compound category but differ in their specific structures and reactivity.

• Aldehydes have at least one hydrogen atom linked to the carbonyl carbon (C=O}). This structural feature leads to their high reactivity.
• Ketones, on the other hand, have two carbon-containing groups attached to the carbonyl carbon, making them somewhat less reactive than aldehydes.

The choice between aldehydes and ketones is crucial in reactions like those with Grignard reagents. For instance, reacting a ketone with a Grignard reagent typically results in the formation of secondary alcohols. In this particular scenario, acetone is the ketone that reacts to form isopropyl alcohol, a secondary alcohol, through a nucleophilic addition mechanism. Understanding the differences and similarities of aldehydes and ketones aids in predicting the outcomes of reactions involving carbonyl chemistry.