Question

Using your roadmaps as a guide, show how to convert cyclohexane and ethanol into racemic 2-acetylcyclohexanone. You must use ethanol and cyclohexane as the source of all carbon atoms in the target molecule. Show all reagents and all molecules synthesized along the way.

Short answer

Question: Describe the step-by-step process of synthesizing racemic 2-acetylcyclohexanone using cyclohexane and ethanol as the sources of all carbon atoms. Answer: To synthesize racemic 2-acetylcyclohexanone using cyclohexane and ethanol as the carbon sources, the following steps need to be performed: 1. Oxidize cyclohexane into cyclohexanone using a strong oxidizing agent like potassium permanganate (KMnO4). 2. Convert ethanol into acetyl chloride by reacting it with thionyl chloride (SOCl2) or phosphorus trichloride (PCl3). 3. Form 2-acetylcyclohexanone by reacting cyclohexanone with acetyl chloride in the presence of a base such as pyridine.

Step-by-step solution

Identify the functional groups of starting materials and target molecule

Cyclohexane is an alkane with the molecular formula C6H12, ethanol is an alcohol with the molecular formula C2H5OH, and 2-acetylcyclohexanone is a ketone with the molecular formula C8H12O. The target molecule contains an acetyl group and a cyclohexanone group.

Oxidation of cyclohexane into cyclohexanone

First, we will oxidize cyclohexane to get cyclohexanone. This can be done using an oxidation reaction with a strong oxidizing agent such as potassium permanganate (KMnO4) or chromium trioxide (CrO3) in an acidic medium. Reaction: Cyclohexane + KMnO4 -> Cyclohexanone

Acetylation of ethanol

Next, we will convert ethanol into acetyl chloride, which can be used to form an acetyl group in the target molecule. This can be done by reacting ethanol with thionyl chloride (SOCl2) or phosphorus trichloride (PCl3). Reaction: Ethanol + PCl3 -> Acetyl chloride + HCl

Formation of 2-acetylcyclohexanone

Finally, we will form the target molecule, racemic 2-acetylcyclohexanone, by reacting cyclohexanone with acetyl chloride in the presence of a base, such as pyridine. Reaction: Cyclohexanone + Acetyl chloride -> 2-Acetylcyclohexanone So, the overall process to convert cyclohexane and ethanol into racemic 2-acetylcyclohexanone is as follows: 1. Oxidation of cyclohexane to cyclohexanone with KMnO4. 2. Acetylation of ethanol with PCl3 to form acetyl chloride. 3. Reaction of cyclohexanone with acetyl chloride in the presence of a base to form the desired product, racemic 2-acetylcyclohexanone.

Key concepts

Oxidation reactions

Oxidation reactions play a crucial role in organic synthesis, particularly when transforming simple alkanes into more complex molecules. In the given process, we start with cyclohexane, an alkane composed solely of carbon and hydrogen. To progress towards our goal of creating 2-acetylcyclohexanone, we must introduce an oxygen atom.

This introduction creates a carbonyl group, essential for forming cyclohexanone.

• The oxidation process involves using strong oxidizing agents such as potassium permanganate (KMnO4) or chromium trioxide (CrO3).
• These agents help in converting the C-H bonds in cyclohexane to C=O bond, resulting in cyclohexanone.
• Due to the strength of these oxidizing agents, reactions often require acidic or neutral conditions to proceed efficiently.

Cyclohexanone is a pivotal intermediate that allows further modifications and integrations to reach the desired end-product. The ability to add and manipulate oxygen-containing functional groups is what allows organic synthesis to create complex molecules.

Acetylation

Acetylation refers to the process of introducing an acetyl group \((-COCH_3)\) into a molecule. This is a fundamental technique in organic synthesis, enabling transformations that expand molecular complexity and functionality.

For the conversion of ethanol to acetyl chloride, acetylation involves specific reagents.

• Ethanol reacts with phosphorus trichloride (PCl3) or thionyl chloride (SOCl2) to form acetyl chloride.
• This step requires careful handling as acetyl chloride is volatile and reactive.
• The acetyl group is then available for further reactions, such as bonding with cyclohexanone to contribute to the formation of the ketone group in the final product.

Acetylation not only facilitates the donation of the acetyl group but also contributes significantly to imparting desirable physical and chemical properties to the resulting compound. This step is crucial in the pathway to synthesizing racemic 2-acetylcyclohexanone as it forms the foundation for constructing the molecule's complex structure.

Racemic mixtures

In organic chemistry, compounds possessing chirality can exist as optical isomers known as enantiomers. A racemic mixture contains equal amounts of these enantiomers, resulting in no net optical activity. This concept is essential when discussing the synthesis of 2-acetylcyclohexanone, as the compound is expected to form as a racemic mixture.

The formation of a racemic mixture occurs because the reaction pathway allows for the creation of both enantiometric forms.

• This is typical in reactions involving non-chiral catalysts or conditions, where no preference is given to either enantiomer.
• Each enantiomer is a mirror image of the other and they typically possess different physiological and chemical properties.
• For synthesizing drugs or substances with specific activity, controlling for racemic mixtures is crucial.

Though a racemic mixture may not counteract the desired effects in all applications, understanding its formation can optimize synthesis pathways and improve the specificity of reactions for desired outcomes. Recognizing the potential for racemic mixtures aids in comprehensively grasping the importance of stereochemistry in organic synthesis.