Propose mechanisms for the nucleophilic acyl substitutions to form N-methylacetamide as shown on the previous page.

Verified step by step guidance

1. Step 1: Identify the starting material and the product. The starting material is benzoyl chloride (PhCOCl), and the product is N-methylacetamide (PhCONHCH3). This reaction involves nucleophilic acyl substitution, where the chlorine atom is replaced by the N-methylamide group.
2. Step 2: Recognize the nucleophile and base. Methylamine (CH3NH2) acts as the nucleophile, and sodium hydroxide (NaOH) serves as the base to neutralize the HCl byproduct formed during the reaction.
3. Step 3: Initiate the mechanism with the nucleophilic attack. The lone pair of electrons on the nitrogen atom of CH3NH2 attacks the carbonyl carbon of benzoyl chloride, forming a tetrahedral intermediate. This step is driven by the electrophilic nature of the carbonyl carbon due to the electron-withdrawing chlorine atom.
4. Step 4: Collapse of the tetrahedral intermediate. The tetrahedral intermediate collapses, expelling the chloride ion (Cl⁻) as a leaving group and forming the amide bond (C-N). This step restores the carbonyl group in the product.
5. Step 5: Neutralization of the byproduct. The expelled HCl reacts with NaOH to form NaCl and water, ensuring the reaction proceeds efficiently without acid buildup. The final product, N-methylacetamide, is formed.

Key Concepts

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction in organic chemistry where a nucleophile attacks the carbonyl carbon of an acyl compound, leading to the replacement of a leaving group (such as a halide) with the nucleophile. This mechanism is crucial for forming amides, esters, and other derivatives from carboxylic acids and their derivatives.

Mechanism Steps

The mechanism of nucleophilic acyl substitution typically involves several key steps: nucleophilic attack on the carbonyl carbon, formation of a tetrahedral intermediate, and subsequent elimination of the leaving group. Understanding these steps is essential for predicting the outcome of the reaction and the stability of intermediates formed during the process.

Role of Base Catalysis

In the provided reaction, sodium hydroxide (NaOH) acts as a base that can deprotonate the nucleophile (methylamine, CH3NH2), enhancing its nucleophilicity. Base catalysis is often employed in nucleophilic acyl substitutions to facilitate the reaction by increasing the reactivity of the nucleophile and stabilizing the transition state.