Question

Outline a synthesis of cumene from cheap, readily available hydrocarbons. Then synthesize phenol from cumene.

Short answer

To synthesize cumene from cheap, readily available hydrocarbons, we start with benzene and propylene and perform the Friedel-Crafts alkylation reaction in the presence of a Lewis acid catalyst, aluminum chloride (AlCl3). This forms cumene. Then, we synthesize phenol from cumene by first converting cumene to cumene hydroperoxide through oxidation using molecular oxygen, and then performing an acid-catalyzed cleavage using sulfuric acid, yielding phenol and acetone.

Step-by-step solution

Formation of Cumene from Benzene and Propylene

In the first step, we perform the Friedel-Crafts alkylation reaction to obtain cumene by combining benzene and propylene in the presence of a Lewis acid catalyst such as aluminum chloride (AlCl3). Benzene (\(C_6H_6\)) + Propylene (\(C_3H_6\)) + AlCl3 → Cumene (\(C_9H_{12}\)) + HCl + AlCl3 This reaction represents the synthesis of cumene by Friedel-Crafts alkylation, in which the alkyl group of propylene is attached to the benzene ring. The Lewis acid catalyst, AlCl3, helps generate carbocation from propylene that attacks the benzene ring. The chloride ion (Cl-) reacts with the hydrogen in the benzene's ring and forms HCl.

Oxidation of Cumene to Cumene Hydroperoxide

To obtain phenol from cumene, we need to convert cumene into cumene hydroperoxide. The oxidation of cumene is performed by bubbling air (O2) through the solution of cumene. Cumene (\(C_9H_{12}\)) + O2 → Cumene Hydroperoxide (\(C_9H_{12}O_2\)) During this reaction, molecular oxygen is added across the benzylic C-H bond of cumene, and cumene hydroperoxide is formed. This step is a radical reaction and requires a radical initiator like benzoyl peroxide.

Acid-Catalyzed Cleavage of Cumene Hydroperoxide

Now, we perform the acid-catalyzed cleavage of cumene hydroperoxide to obtain phenol and acetone. The reaction takes place in the presence of a strong acid, such as sulfuric acid (H2SO4). Cumene Hydroperoxide (\(C_9H_{12}O_2\)) + H2SO4 → Phenol (\(C_6H_5OH\)) + Acetone (\(CH_3COCH_3\)) + H2SO4 Under acidic conditions, cumene hydroperoxide rearranges to form phenol and acetone products. This step is an important industrial process since both phenol and acetone are valuable chemicals in the chemical industry. In summary, we have successfully outlined the synthesis of cumene from cheap, readily available hydrocarbons (benzene and propylene) through Friedel-Crafts alkylation. We then synthesized phenol from cumene by forming cumene hydroperoxide through oxidation, followed by an acid-catalyzed cleavage to yield phenol and acetone products.

Key concepts

Friedel-Crafts Alkylation

Friedel-Crafts Alkylation is a crucial reaction in organic chemistry used to form carbon-carbon bonds. This versatile method involves introducing an alkyl or acyl group onto an aromatic ring, typically benzene. In our synthesis of cumene, we employ the Friedel-Crafts alkylation to combine benzene with propylene. This reaction is facilitated by a Lewis acid catalyst, such as aluminum chloride (AlCl3).

Here's how it works:

• The Lewis acid catalyst aids in generating a carbocation from propylene, making it a strong electrophile.
• This carbocation then attacks the electron-rich benzene ring, leading to the formation of cumene.
• As a result, the benzene ring gains an alkyl group from propylene, forming cumene.

The importance of this reaction cannot be overstated. It's a fundamental step in organic synthesis because it allows the formation of complex molecules from simpler components. However, one must carefully control reaction conditions to minimize by-products and achieve high yields.

Oxidation Reactions

Oxidation reactions play a pivotal role in converting substances into more oxidized forms. In the transformation of cumene to phenol, oxidation reactions are employed to form cumene hydroperoxide. This involves bubbling air (O2) through cumene.

The process:

• Molecular oxygen is introduced to attack the benzylic C-H bond in cumene through a radical mechanism.
• A radical initiator, such as benzoyl peroxide, can be used to jumpstart the reaction.
• The result is the formation of cumene hydroperoxide, a crucial intermediate for the next step.

Oxidation reactions are essential in organic synthesis because they enable the conversion of simple hydrocarbon substrates into more functionalized products. This transformation is guided by controlling molecular oxygen's interaction with the substrate, resulting in the desired oxidized product.

Acid-Catalyzed Reactions

Acid-catalyzed reactions are vital in organic chemistry, serving as mechanisms to rearrange or break down compounds. In our synthesis of phenol, the acid-catalyzed reaction involves breaking down cumene hydroperoxide.

Here's what happens:

• The presence of a strong acid, like sulfuric acid (H2SO4), catalyzes the cleavage of cumene hydroperoxide.
• This results in the production of phenol and acetone, both valuable chemical products.
• The reaction showcases how acids can act as catalysts, providing a pathway for otherwise slow or unlikely transformations.

Acid-catalyzed reactions are prominent in industrial chemistry due to their ability to efficiently drive reactions to completion. By leveraging the catalyst's ability to stabilize transition states, we achieve the desired rearrangement or breakdown of compounds into commercially important chemicals.

Industrial Chemical Processes

Industrial chemical processes are processes designed for mass production of chemical substances, supporting various sectors. The synthesis of phenol from cumene is an excellent example of such a process, demonstrating efficiency and utility in industrial settings.

Key aspects include:

• Utilizing readily available hydrocarbons like benzene and propylene reduces costs and ensures a sustainable supply chain.
• The sequence leveraging Friedel-Crafts alkylation, oxidation, and acid-catalyzed reactions allows for the systematic production of phenol, an important commodity chemical.
• Phenol is used extensively in the production of plastics, resins, and pharmaceuticals, making its efficient synthesis crucial to meet industrial demand.

By integrating these chemical processes, industries achieve high yields of essential chemicals while minimizing waste and energy consumption. The method exemplifies how chemical engineering principles provide scalable solutions for producing valuable products while maintaining environmental and economic considerations.