Question

Ethyl acetate is obtained when methylmagnesium iodide reacts with (a) ethyl formate (b) acetyl chloride (c) carbon dioxide (d) ethyl chloroformate

Short answer

Methylmagnesium iodide reacts with ethyl chloroformate to form ethyl acetate.

Step-by-step solution

Understanding the Reaction

When determining the product of a reaction involving Grignard reagents like methylmagnesium iodide, we need to consider how this reagent behaves. It acts as a nucleophile and will attack electrophilic carbon centers in molecules. The question is asking which compound, when reacted with methylmagnesium iodide, will yield ethyl acetate.

Evaluating the Options

Examine each compound to determine how it might react with methylmagnesium iodide: 1. **Ethyl formate (CHOOC2H5):** It has an electrophilic carbonyl carbon, which can be attacked by the Grignard reagent, potentially yielding a tertiary alcohol and not an ester like ethyl acetate. 2. **Acetyl chloride (CH3COCl):** Reacts with Grignard reagents to generally give ketones or tertiary alcohols considering the order of reaction steps. 3. **Carbon dioxide (CO2):** Generally forms carboxylic acids with Grignard reagents, not esters. 4. **Ethyl chloroformate (ClCOOC2H5):** Reacting with methylmagnesium iodide could yield ethyl acetate because it allows nucleophilic acyl substitution, replacing the chloride with a methyl group leading to ethyl acetate.

Drawing Reaction Mechanism

For option **(d) Ethyl chloroformate**, the reaction with methylmagnesium iodide proceeds as follows: 1. The electron-rich carbon of the methyl group in methylmagnesium iodide attacks the carbonyl carbon in ethyl chloroformate. 2. This leads to a tetrahedral intermediate, which is unstable and results in the loss of a chloride ion. 3. The product formed is ethyl acetate, which is the desired ester.

Key concepts

Nucleophile

A nucleophile is a chemical species that donates electron pairs to an electron-deficient atom, typically a carbon, in a chemical reaction. Grignard reagents like methylmagnesium iodide are excellent examples of nucleophiles. They contain a carbon that has partial negative charge, making it eager to share its electrons. When a nucleophile attacks an electrophile, which is a positively charged or electron-poor site, a bond is formed between them. Grignard reagents are particularly reactive because the carbon attached to the magnesium ion is very electron-rich. This characteristic of Grignard reagents makes them versatile in creating new carbon-carbon bonds, an essential process in organic synthesis. Nucleophilic reactions are influenced by factors such as the concentration of the nucleophile, the solvent used, and the nature of the electrophile. Each of these elements can affect the rate and outcome of the reaction, making them crucial considerations in any organic chemistry reaction.

Electrophilic Substitution

Electrophilic substitution is a reaction where an electrophile replaces an atom or a group of atoms in a compound. In the context of Grignard reagent reactions, the focus is often on the ability of the nucleophile to effectively displace certain atoms. Although in some reactions involving Grignard reagents, substitution is not always straightforward, the reaction with ethyl chloroformate showcases the concept beautifully. Here, the electrophilic carbon of the carbonyl group is attacked by the nucleophilic methyl group from the Grignard reagent, leading to the displacement of a chloride ion. This process is referred to as nucleophilic acyl substitution, and it results in forming the ester, ethyl acetate. Understanding this mechanism provides insights into how Grignard reagents can transform even complex molecules by effectively substituting atoms or groups to form desired products.

Esters

Esters are a class of organic compounds characterized by the presence of a carbonyl group (\[ C=O \] ) attached to an oxygen atom that is bonded to another carbon-containing group. Ethyl acetate, the target product in our reaction, is a typical ester formed from ethanol and acetic acid or its derivatives.They play a vital role in biochemistry and industrial applications due to their pleasant aromas and volatility. Esters are commonly used in flavorings, perfumes, and as solvents. In solutions involving Grignard reagents, esters can be formed through nucleophilic acyl substitution reactions, as seen when methylmagnesium iodide reacts with ethyl chloroformate. The ability to form esters through such synthetic routes is significant because it allows chemists to design complex molecules for various industrial applications.

Reaction Mechanism

The reaction mechanism illustrates how reactants transform into products through a series of steps. For Grignard reactions with ethyl chloroformate, understanding this mechanism is crucial. 1. **Initiation Step:** The nucleophile (methylmagnesium iodide) attacks the carbonyl carbon of ethyl chloroformate. This moment is vital, as the methyl group initiates the process by donating its electron pairs to form a new bond. 2. **Intermediate Formation:** This nucleophilic attack results in a tetrahedral intermediate. This intermediate is temporarily stable but will eventually break down. 3. **Substitution and Product Formation:** The unstable intermediate collapses back into a more stable structure by kicking out the chloride ion. This step completes the substitution and forms ethyl acetate. Each stage in the mechanism is important because it highlights the interplay between nucleophiles and electrophiles, ultimately leading to the successful synthesis of esters like ethyl acetate.