Chapter 23: Problem 589

4-n-Hexylresorcinol is used in certain antiseptics. Outline its preparation starting with resorcinol and any aliphatic reagents.

Short Answer

Expert verified

To prepare 4-n-Hexylresorcinol starting with resorcinol and an aliphatic reagent, perform an electrophilic aromatic substitution reaction using 1-bromohexane and anhydrous aluminum chloride (AlCl3) as a catalyst. Mix resorcinol and 1-bromohexane in dichloromethane (CH2Cl2), add AlCl3, and heat the reaction mixture under reflux. Monitor the reaction progress, and after completion, hydrolyze the aluminum complex, filter the solid, and extract the product from the aqueous layer. Dry and purify the organic layer to yield 4-n-Hexylresorcinol.

Step by step solution

Identify the reagents

Firstly, we need to identify the appropriate aliphatic reagent for the formation of 4-n-Hexylresorcinol. The desired product contains a hexyl group (six carbons), so we will use 1-bromohexane as the aliphatic reagent for this synthesis. Furthermore, we should also use anhydrous aluminum chloride (AlCl3) as a catalyst to facilitate the electrophilic aromatic substitution reaction.

Perform electrophilic aromatic substitution

To synthesize 4-n-Hexylresorcinol, we need to perform an electrophilic aromatic substitution reaction on resorcinol. In this reaction, the bromine atom in 1-bromohexane will act as a leaving group, and the hexyl group will be introduced at the para-position relative to the -OH group in resorcinol. The detailed steps are as follows: 1. Mix resorcinol and 1-bromohexane in a suitable solvent, such as dichloromethane (CH2Cl2), in a round-bottom flask. 2. Add anhydrous aluminum chloride (AlCl3) to the reaction mixture to serve as a catalyst. 3. Heat the reaction mixture under reflux to increase the reaction rate. 4. Keep an eye on the progress of the reaction using thin-layer chromatography (TLC) or any other suitable analytical method. 5. After the reaction is complete, cool the reaction mixture to room temperature. 6. Hydrolyze the aluminum complex formed during the reaction by adding water, followed by aqueous acid (for example, concentrated hydrochloric acid). 7. Filter the solid aluminum hydroxide (Al(OH)3) produced after the hydrolysis. 8. Extract the product (4-n-Hexylresorcinol) from the aqueous layer using an organic solvent, such as dichloromethane (CH2Cl2). 9. Dry the organic layer using anhydrous sodium sulfate (Na2SO4) and evaporate the solvent. 10. Purify the 4-n-Hexylresorcinol by recrystallization or column chromatography to yield the desired product. In summary, the preparation of 4-n-Hexylresorcinol can be achieved by performing an electrophilic aromatic substitution reaction between resorcinol and 1-bromohexane in the presence of anhydrous aluminum chloride as a catalyst.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry used to modify aromatic rings, such as benzene derivatives. In this reaction, an electrophile replaces one of the hydrogen atoms on the aromatic ring. The electrophile is typically formed from a reagent that becomes more electron-deficient in the presence of a catalyst or due to the external reaction conditions.

The reaction mechanism for EAS includes several steps: formation of the electrophile, generation of an arenium ion intermediate, and deprotonation to restore aromaticity. For 4-n-Hexylresorcinol synthesis, the electrophile is a hexyl cation created when 1-bromohexane interacts with a Lewis acid, anhydrous aluminum chloride (AlCl3), which induces the cleavage of the C-Br bond.

The significance of this mechanism lies in the formation of new carbon-carbon bonds, which is essential in the field of organic synthesis to obtain various functionalized aromatic compounds.

Organic Synthesis Reagents

During the synthesis of 4-n-Hexylresorcinol, specific organic synthesis reagents are integral to achieving the desired transformation. The primary reagents include the substrate, resorcinol, and the alkylating agent, 1-bromohexane.

Resorcinol serves as the aromatic starting material, which holds the reactive positions that allow electrophilic attack. 1-Bromohexane is an alkyl halide that contains the carbon fragment to be attached to the aromatic ring. Its structure is chosen based on the length of the carbon chain desired in the final product.

Other reagents and solvents play supportive roles. Dichloromethane acts as a medium facilitating the reaction, while anhydrous aluminum chloride serves as a powerful Lewis acid, increasing the electrophilicity of the alkyl halide. After the reaction, hydrochloric acid is used for hydrolysis, sodium sulfate for drying, and various solvents for purification. These reagents are all selected based on their specific roles and compatibility with the reaction conditions.

Anhydrous Aluminum Chloride Catalyst

Anhydrous aluminum chloride (AlCl3) is a potent Lewis acid often used as a catalyst in EAS reactions. A catalyst is a substance that increases the rate of a chemical reaction without being consumed. In the synthesis of 4-n-Hexylresorcinol, AlCl3 plays a critical role; it facilitates the generation of a more reactive electrophile by accepting an electron pair from the bromine atom in 1-bromohexane.

By doing so, it also stabilizes the resultant carbocation intermediate, making it easier for the electrophilic attack on the resorcinol ring. The unique ability of AlCl3 to handle these tasks without being part of the final product makes it invaluable in organic reactions that require the formation of carbon-carbon bonds. Effective use of such catalysts is crucial for reaction efficiency and economic viability in industrial organic synthesis.

Reaction Mechanisms in Organic Chemistry

Understanding reaction mechanisms in organic chemistry provides insights into how and why reactions occur as they do. A reaction mechanism details the step-by-step sequence of elementary steps that lead to the transformation of reactants to products.

In the context of 4-n-Hexylresorcinol synthesis, the mechanism involves an initial attack of the electrophile (hexyl cation) on the resorcinol to form a sigma complex, followed by deprotonation to regenerate the aromatic structure. Monitoring tools such as thin-layer chromatography (TLC) help chemists to observe these processes in real-time and confirm that the reaction is proceeding correctly.

Furthermore, the reaction mechanisms explain the role of solvents, the need for anhydrous conditions, and the function of various work-up steps, such as hydrolysis and extraction. Recognizing these elements empowers students and chemists to design, troubleshoot, and optimize organic reactions for research and industrial applications.

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4-n-Hexylresorcinol is used in certain antiseptics. Outline its preparation starting with resorcinol and any aliphatic reagents.

Short Answer

Step by step solution

Identify the reagents

Perform electrophilic aromatic substitution

Key Concepts

Electrophilic Aromatic Substitution

Organic Synthesis Reagents

Anhydrous Aluminum Chloride Catalyst

Reaction Mechanisms in Organic Chemistry

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