Problem 149 - A Complete Resource Book in Chemistry for JEE Main

Question

List I contains the Grignard reagent and carbonyl compounds or ethylene oxide used to prepare the alcohols of list II. Match list I and list II. List I 1\. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Mg} \mathrm{X}+\mathrm{H}_{2} \mathrm{CO}\) 2\. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COCH}_{3}+\mathrm{CH}_{3} \mathrm{MgX}\) \(3 .\) 4\. \(\mathrm{Ph} \mathrm{CH}_{2} \mathrm{CHO}+\mathrm{CH}_{3} \mathrm{MgX}\) List II (i) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (ii) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (iii) CCC(CO)c1ccccc1 (iv) \(\mathrm{PhCH}_{2} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}\) The correct matching is \(\begin{array}{lll}1 & 2 & 3\end{array}\) 4 (a) (ii) (i) (ii) (iii) (b) (ii) (i) (ii) (iv) (c) (i) (ii) (ii) (iii) (d) (ii) (i) (iv) (ii)

Step-by-Step Solution

Answer

(d) (ii) (i) (iv) (ii)

Step 1: Analyzing Reactions of Grignard Reagents with Formaldehyde

In the reaction 1 from list I: \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Mg} \mathrm{X}+\mathrm{H}_{2} \mathrm{CO} \), the Grignard reagent \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Mg} \mathrm{X} \) reacts with formaldehyde \( \mathrm{H}_{2} \mathrm{CO} \). This results in the addition of the ethyl group \( \mathrm{CH}_{3} \mathrm{CH}_{2} \) to the formaldehyde, forming \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} \) (ethanol). This corresponds to item (ii) from list II.

Step 2: Analyzing Reactions Involving Methyl Magnesium Halide

In reaction 2: \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COCH}_{3}+\mathrm{CH}_{3} \mathrm{MgX} \), propanone \( \left(\mathrm{COCH}_{3}\right) \) reacts with \( \mathrm{CH}_{3} \mathrm{MgX} \), leading to the formation of \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} \). This is indicated by item (i) in list II.

Step 3: Combining Phenyl Acetaldehyde and Methyl Magnesium Halide

In reaction 4: \( \mathrm{Ph} \mathrm{CH}_{2} \mathrm{CHO}+\mathrm{CH}_{3} \mathrm{MgX} \), phenylacetaldehyde \( \mathrm{PhCH}_{2} \mathrm{CHO} \) reacts with methyl magnesium halide to yield \( \mathrm{PhCH}_{2} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3} \), which matches item (iv) in list II.

Key Concepts

Alcohol Synthesis

Alcohol synthesis is a crucial aspect in organic chemistry, especially when discussing Grignard reactions. Grignard reagents are organomagnesium compounds that enable the formation of carbon-carbon bonds. This is vital in creating alcohols from different starting materials, such as carbonyl compounds and ethylene oxide. In a typical reaction, a Grignard reagent reacts with a carbonyl compound to form an alcohol. Each reaction involves the nucleophilic addition of the Grignard reagent to the electrophilic carbon present in the carbonyl group. After the addition, the reaction is quenched with water or an acid to yield the respective alcohol.
Grignard reactions are one of the most flexible and preferred methods for transforming basic materials into valuable alcohol products in the lab.

Carbonyl Compounds

Carbonyl compounds are essential in Grignard reactions and play a key role in alcohol synthesis. They contain a carbon-oxygen double bond, which is highly reactive and susceptible to nucleophilic attack. There are several types of carbonyl compounds including aldehydes and ketones. In Grignard reactions:

• Aldehydes generally produce secondary alcohols.
• Ketones yield tertiary alcohols.
• Formaldehyde is a special case that produces primary alcohols.

The reactivity of carbonyl compounds makes them excellent partners for Grignard reagents, which transform them into various complex organic molecules when combined.

Ethylene Oxide

Ethylene oxide is a highly reactive cyclic ether commonly used in Grignard reactions to synthesize ethylene-based alcohols. When a Grignard reagent reacts with ethylene oxide, it opens the three-membered ring in the oxidation addition process. This typically results in the formation of a primary alcohol with two additional carbons compared to the original Grignard reagent.
The reaction with ethylene oxide is an elegant method for extending the carbon backbone of a molecule, providing a simple and efficient means to synthesize longer carbon chains with new alcohol functional groups.

Formaldehyde

Formaldehyde is the simplest aldehyde and plays a fascinating role in Grignard reactions for alcohol synthesis. Unlike other carbonyl compounds, when formaldehyde reacts with a Grignard reagent, it yields a primary alcohol. This reaction:

• Involves the nucleophilic addition of the organomagnesium compound to the carbonyl carbon of formaldehyde.
• Is quenched with water to give the extended alcohol chain.

This makes formaldehyde a unique candidate because it adds only one carbon to the alcohol structure, offering a direct path to primary alcohols without branching.

Methyl Magnesium Halide

Methyl magnesium halide (\(\mathrm{CH}_{3}\mathrm{MgX}\)) is a type of Grignard reagent that is common in organic synthesis. It acts as a strong nucleophile, attacking carbonyl carbons in a variety of compounds. When it reacts with:

• Propanone, it yields a tertiary alcohol.
• Phenylacetaldehyde, it forms a secondary alcohol.

This reagent is versatile and offers numerous possibilities for generating alcohols with different levels of complexity through the careful selection of reacting partners.

Phenylacetaldehyde

Phenylacetaldehyde is an aromatic aldehyde with a structure incorporating both a benzene ring and an aldehyde group. When it undergoes Grignard reactions, it particularly reacts with methyl magnesium halide. In such reactions:

• The Grignard reagent adds to the aldehyde carbonyl group.
• The result is the formation of a secondary alcohol after quenching.

This dual nature of phenylacetaldehyde, pairing aromatic and aldehyde characteristics, enriches the diversity of products obtainable and highlights its importance in creating complex alcohol structures.