Problem 27 - Chemistry and Chemical Reactivity

Question

Write an equation for the preparation of ethylbenzene from benzene and an appropriate compound containing an ethyl group.

Step-by-Step Solution

Answer

Benzene reacts with ethyl chloride in the presence of AlCl₃ to form ethylbenzene and HCl.

Step 1: Understand the Reaction

The goal is to produce ethylbenzene by adding an ethyl group to a benzene ring. This type of reaction is a Friedel-Crafts alkylation.

Step 2: Identify Reactants

For the Friedel-Crafts alkylation, we need benzene (C₆H₆) and an ethyl group source. A common ethyl group source is ethyl chloride (C₂H₅Cl).

Step 3: Identify the Catalyst

In Friedel-Crafts alkylation, an aluminum chloride (AlCl₃) catalyst is often used to facilitate the reaction.

Step 4: Write the Equation

Combine benzene with ethyl chloride in the presence of AlCl₃ to form ethylbenzene and HCl as a byproduct. The equation is: \[ ext{C}_6 ext{H}_6 + ext{C}_2 ext{H}_5 ext{Cl} ightarrow[ ext{AlCl}_3] ext{C}_6 ext{H}_5 ext{C}_2 ext{H}_5 + ext{HCl} \]

Step 5: Double-check the Equation

Verify that all the atoms are balanced and that the reactants are rearranged to form the correct product and byproduct.

Key Concepts

Benzene Reactions

Benzene is a fascinating organic compound known for its stability and unique reactions. Due to its aromatic nature, benzene often undergoes substitution reactions rather than addition reactions. In a substitution reaction, an existing hydrogen atom in benzene is replaced with a new group, like an ethyl group. This forms a new product without losing the benzene’s characteristic aromatic ring.

One of the most common reactions involving benzene is the Friedel-Crafts alkylation, where an alkyl group is introduced to the benzene ring. In this process, a catalyst like aluminum chloride (AlCl₃) helps to facilitate the reaction. The benzene retains its stable aromatic structure by substituting one of its hydrogens with an ethyl group, forming ethylbenzene. While the process is favorable for forming specific products, it may require careful handling as catalysts like AlCl₃ can be sensitive to air and moisture.

Ethylbenzene Preparation

Creating ethylbenzene from benzene involves a specific chemical process called Friedel-Crafts alkylation. This involves introducing an ethyl group to the benzene ring. To achieve this, benzene is reacted with an appropriate compound that contains an ethyl group.

In this case, ethyl chloride (C₂H₅Cl) is commonly used. It acts as the source of the ethyl group, donating it to replace one of benzene’s hydrogen atoms. The catalyst aluminum chloride (AlCl₃) plays a crucial role here by generating a unique intermediate that will allow the reaction to proceed. The result is ethylbenzene (C₆H₅C₂H₅) along with hydrochloric acid (HCl) as a byproduct. One thing to note is to ensure proper handling and disposal of byproducts as part of responsible chemical practice.

Chemical Equation Balancing

Balancing chemical equations is an essential skill in chemistry that ensures matter is conserved during reactions. In a balanced equation, the number of each type of atom on the reactants side equals that on the products side.

Consider the Friedel-Crafts alkylation that prepares ethylbenzene: \[\text{C}_6\text{H}_6 + \text{C}_2\text{H}_5\text{Cl} \rightarrow[\text{AlCl}_3] \text{C}_6\text{H}_5\text{C}_2\text{H}_5 + \text{HCl}\]Each type of atom is counted to confirm the balance:

• Carbon atoms: 6 in benzene + 2 in ethyl chloride = 8 in ethylbenzene.
• Hydrogen atoms: 6 in benzene + 5 in ethyl chloride = 11 in ethylbenzene + 1 in HCl.
• Chloride atom: 1 in ethyl chloride = 1 in HCl.

This check verifies mass conservation, making sure no atom is lost or unaccounted for in the reaction process. Keeping equations balanced ensures that the resulting stoichiometry is correct, which is crucial in controlling the amounts of products and reactants precisely.