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

The compounds are (b) acetone and isopropyl alcohol.

Step 1: Analyzing the Reaction with Grignard Reagent

The problem states that compound 'A' reacts with methyl magnesium iodide, which is a Grignard reagent. Grignard reagents react with carbonyl compounds to form an alcohol after hydrolysis. Here, compound 'A' would likely be a carbonyl compound (aldehyde or ketone).

Step 2: Formation of the Addition Product

The reaction between 'A' and methyl magnesium iodide forms an addition product. This product, upon hydrolysis, would result in an alcohol compound 'B'. We need to determine this intermediate and final alcohol.

Step 3: Understanding the Victor Meyer's Test

The Victor Meyer test is used to classify alcohols and blue color indicates a secondary alcohol. So, compound 'B' should be a secondary alcohol.

Step 4: Matching Compound 'B' to a Secondary Alcohol

Given that 'B' results from the hydrolysis and provides a blue color in Victor Meyer's test, compound 'B' should be a secondary alcohol like isopropyl alcohol.

Step 5: Identifying Compound 'A'

To form isopropyl alcohol from reaction with a Grignard reagent, the precursor carbonyl compound 'A' should be acetone. This is because Grignard reagents reacting with acetone produce isopropyl alcohol, which matches our compound 'B'.

Step 6: Concluding 'A' and 'B'

Thus, based on the reaction and the type of alcohol formed, compound 'A' is acetone and compound 'B' is isopropyl alcohol.

Key Concepts

Victor Meyer's Test

Victor Meyer's test is a chemical test used to identify and distinguish primary, secondary, and tertiary alcohols through a colorimetric approach. During this test, different types of alcohols are converted into their respective iodides, which are then reacted with silver nitrate in a nitrate solution to produce specific color changes. These color changes assist in classifying the alcohols effectively.

In this specific test, secondary alcohols give a blue color, primary alcohols turn red, and tertiary alcohols remain colorless. It's quite fascinating how a simple color change can provide essential information about the structure and classification of alcohols.

The blue color observed in the Victor Meyer's test for the compound 'B' in our problem indicates that 'B' is a secondary alcohol. This aligns with the observations that result in isopropyl alcohol, a classic example of a secondary alcohol.

Secondary Alcohols

Secondary alcohols are organic compounds in which the hydroxyl group (-OH) is attached to a carbon atom, which is itself connected to two other carbon atoms. This structure is easy to recognize:

• The hydroxyl group (-OH) is bonded to a secondary carbon atom.
• The remaining bonds of this carbon atom are with two other distinct carbon atoms.

Due to this configuration, secondary alcohols can be easily illustrated with the example of isopropyl alcohol, also known as 2-propanol.

In secondary alcohols, the carbon atom holding the -OH group is bonded to a hydrogen atom and two carbon chains. This bonding pattern is what gives secondary alcohols their unique properties, such as their reactivity and the ability to form products like ketones upon oxidation.

Grignard Reagents

Grignard reagents are a set of organomagnesium compounds used in organic synthesis to facilitate the formation of carbon-carbon bonds. These reagents are very reactive and have the general formula RMgX, where R is a hydrocarbon group, and X is a halide.

The interaction between Grignard reagents and carbonyl compounds is quite significant because it enables the formation of alcohols after hydrolysis. They are commonly used in organic chemistry due to their high reactivity and precision in achieving desired synthetic outcomes.

In our problem, the Grignard reagent methyl magnesium iodide reacts with compound 'A', a carbonyl compound, to ultimately form a secondary alcohol after hydrolysis, aligning with the properties of isopropyl alcohol. This reaction is fundamental in many organic synthesis pathways and exemplifies the versatility of Grignard reagents in forming alcohols.

Carbonyl Compounds

Carbonyl compounds are organic molecules that contain a carbonyl group, which is a carbon double-bonded to an oxygen atom (C=O). This functional group is crucial in organic chemistry, as it serves as a building block for other functional groups, such as alcohols, ketones, and aldehydes.

These compounds are highly reactive, making them essential intermediates in many chemical reactions. Among carbonyl compounds, ketones and aldehydes are the most prominent:

• Ketones have the carbonyl group bonded to two carbon atoms, while aldehydes have it bonded to one carbon and one hydrogen atom.

In the problem at hand, compound 'A' is a carbonyl compound, specifically acetone, which reacts with the Grignard reagent to ultimately form isopropyl alcohol. Understanding these compounds is vital since they are involved in transforming into various functional groups essential for building complex molecules in synthetic chemistry.