Question

The reaction of an aromatic aryl chloride and phenol in the presence of the base \(\mathrm{NaOH}\) or pyridine, is called (a) Kolbe's reaction (b) Perkin reaction (c) Sandmeyer's reaction (d) Schotten-Baumann reaction

Short answer

(d) Schotten-Baumann reaction.

Step-by-step solution

Identify Reaction Components

The problem mentions an aromatic aryl chloride and phenol as the reactants, and a base such as \( \mathrm{NaOH} \) or pyridine used in the reaction.

Understand Reaction Mechanism

This setup is typical of a reaction where phenol reacts with acyl chlorides in the presence of a base, often leading to the formation of esters or more complex compounds. It suggests a substitution reaction takes place.

Recall Named Reactions

There are several well-known named reactions involving aromatic compounds. Kolbe's reaction involves the conversion of sodium phenoxide to salicylic acid through carbon dioxide. Perkin reaction involves the formation of cinnamic acids. Sandmeyer's reaction involves halogenation using diazonium salts. Schotten-Baumann reaction involves the formation of amides or esters using acid chlorides and a base.

Match Reaction to Description

The Schotten-Baumann reaction describes the use of a base like \( \mathrm{NaOH} \) or pyridine to facilitate the reaction between acyl chlorides and compounds like phenol to form esters or similar compounds, matching the reaction in question.

Key concepts

Schotten-Baumann Reaction

The Schotten-Baumann reaction is a classic named organic reaction widely used in the synthesis of amides and esters. This reaction involves an acyl chloride and a compound containing an active hydrogen atom, such as phenol or an amine, in the presence of a basic medium like sodium hydroxide (\(\mathrm{NaOH}\)) or an organic base like pyridine.

In this reaction, the acyl chloride reacts with the base first, forming an active intermediate. The intermediate then reacts with the phenolic component to form an ester or with an amine to form an amide. This step-wise mechanism minimizes unwanted side reactions and enhances the yield of the desired ester or amide compound. The base serves two critical roles:

• Neutralization: It neutralizes the hydrochloric acid formed as a by-product, preventing it from interfering with the reaction.
• Facilitation: It helps transfer the acyl group to the phenol or amine by forming a more reactive intermediate.

The use of a base also makes this reaction suitable for temperature control, as it minimizes the conditions under which sensitive compounds can degrade.

This technique is valuable in both industrial and laboratory settings due to its efficiency and simplicity. It is referred to as the Schotten-Baumann reaction, in honor of its discoverers Rudolf Schotten and Eugen Baumann.

Ester Formation

Ester formation is a fundamental concept in organic chemistry. Esters are compounds characterized by the functional group \(-COOR\), where R represents an organic substituent.

Typically, esters are synthesized through a reaction between an alcohol and a carboxylic acid, a process known as esterification. However, an alternative approach involves the reaction of phenols or alcohols with acyl chlorides, particularly in a Schotten-Baumann reaction.

• Traditional Esterification: Uses acids and alcohols, often requiring a catalyst like concentrated sulfuric acid for better efficiency.
• Schotten-Baumann Method: Involves acyl chlorides and alcohols or phenols, and often provides higher yields due to the more reactive nature of acyl chlorides.

This ester formation method through acyl chlorides presents several advantages:

The reaction typically proceeds faster and at lower temperatures since acyl chlorides are more reactive than carboxylic acids. Additionally, the removal of side products such as hydrochloric acid is managed more efficiently by the basic conditions, which maintain the reaction's cleanliness and prevent damage to sensitive functional groups. This makes the Schotten-Baumann method advantageous for producing complex esters required in fragrances and pharmaceuticals.

Substitution Reactions

Substitution reactions are a broad class of chemical reactions in which one functional group in a chemical compound is replaced by another. These reactions are a cornerstone of organic chemistry, helping synthesize a multitude of essential products, including pharmaceuticals and agricultural chemicals.

In the context of the Schotten-Baumann reaction, the substitution involves displacement of the chloride ion of an acyl chloride by a phenolic group or an amine. The general cycle of these reactions consists of three main phases:

• Initiation: Activation of the leaving group by the base, making it more susceptible to nucleophilic attack.
• Attack: The nucleophile (e.g., phenol) attacks the activated acyl chloride, forming a tetrahedral intermediate.
• Formation: The intermediate collapses, expelling the leaving group (usually chloride in this case) and forming the desired product.

Substitution reactions are crucial because they provide a versatile framework for modifying molecular structures, allowing chemists to build complex molecules with precision. This is especially beneficial in drug discovery and materials science, where controlled molecular transformations are key. The Schotten-Baumann process exemplifies a specific type of substitution reaction geared towards producing esters and amides, offering a reliable methodology for obtaining high-quality chemical structures.