Problem 186 - A Complete Resource Book in Chemistry for JEE Main

Question

How many moles of methyl magnesium iodide in ether will react with a molecule of ethylchloroformate to form a \(3^{\circ}\) alcohol?

Step-by-Step Solution

Answer

1 mole based on 1:1 molar ratio.

Step 1: Analyze the Reaction

The reaction between a Grignard reagent such as methyl magnesium iodide (CH₃MgI) and ethyl chloroformate (ClCOOC₂H₅) produces a tertiary alcohol. It involves the nucleophilic attack of the carbon of CH₃MgI on the carbonyl carbon of ethyl chloroformate.

Step 2: Determine the Molar Ratios

The reaction between methyl magnesium iodide and ethyl chloroformate proceeds in a 1:1 molar ratio. This is based on the stoichiometry of the reaction: each molecule of ethyl chloroformate reacts with one molecule of methyl magnesium iodide to form the alcohol.

Step 3: Calculate the Number of Moles Required

Given that the reaction is in a 1:1 molar ratio, 1 mole of ethyl chloroformate will require 1 mole of methyl magnesium iodide to complete the reaction and form the tertiary alcohol.

Key Concepts

Methyl Magnesium Iodide

Methyl magnesium iodide is a type of Grignard reagent useful in organic synthesis. Grignard reagents are named after their inventor, Victor Grignard, who was honored with a Nobel Prize for this discovery.

• Grignard reagents are made by reacting magnesium metal with alkyl or aryl halides in an ether solvent, such as diethyl ether. This particular reagent, methyl magnesium iodide, is made from methyl iodide and magnesium.
• The structure of methyl magnesium iodide includes a highly reactive magnesium-carbon bond, which characterizes it as a strong nucleophile.

The reactivity of the carbon-magnesium bond allows it to attack electrophilic carbon atoms, making Grignard reagents versatile and potent in forming carbon-carbon bonds.
The production of methyl magnesium iodide is sensitive to moisture and should be conducted under anhydrous (without water) conditions to prevent the reagent from reacting with water instead of the intended compound.

Ethyl Chloroformate Reaction

Ethyl chloroformate is an important compound in organic chemistry, often used as a reagent to introduce protective groups or as a building block for larger molecules. This compound consists of a carbonyl group flanked by a chlorine atom and an ethoxy group.
In the context of reactions with Grignard reagents, ethyl chloroformate serves as an electrophile that can be attacked by a nucleophile.

• When exposed to methyl magnesium iodide, the carbonyl carbon of ethyl chloroformate is susceptible to nucleophilic attack. This creates a short-lived intermediate where the new carbon-carbon bond forms.
• The chlorine in ethyl chloroformate acts as a good leaving group, substituting the Grignard reagent into the compound effectively.

This process illustrates the principle of nucleophilic acyl substitution, a common mechanism in organic chemistry, especially in forming complex molecules from simpler starting materials.

Tertiary Alcohol Formation

The formation of tertiary alcohols is one of the major applications of reactions involving Grignard reagents and certain electrophiles, such as ethyl chloroformate. In this reaction, the methyl group from the methyl magnesium iodide bonds with the electrophilic center of ethyl chloroformate.

• This process results in an intermediate compound that, upon hydrolysis, yields a tertiary alcohol.
• The particular reaction between methyl magnesium iodide and ethyl chloroformate follows a 1:1 molar ratio, meaning for every mole of ethyl chloroformate, a mole of methyl magnesium iodide is required to produce a tertiary alcohol.

Tertiary alcohols have unique properties, as they do not oxidize easily to form carbonyl compounds, setting them apart from primary and secondary alcohols. This makes tertiary alcohols valuable in various chemical syntheses and industrial processes. Through this process, chemists can efficiently synthesize complex alcohol structures, created from very simple reagents, demonstrating the power and flexibility of Grignard chemistry.