Question

Ether is obtained by the reaction of ethyl alcohol and \(\mathrm{H}_{2} \mathrm{SO}_{4}\) at (a) \(474 \mathrm{~K}\) (b) \(383 \mathrm{~K}\) (c) \(413 \mathrm{~K}\) (d) \(273 \mathrm{~K}\)

Short answer

Ether is obtained at (c) 413 K.

Step-by-step solution

Understanding the Reaction Conditions

Ether is commonly prepared by the dehydration of ethyl alcohol (ethanol) in the presence of concentrated sulfuric acid (\(\mathrm{H}_{2}\mathrm{SO}_{4}\)). This dehydration reaction favors the formation of ether at specific temperature conditions.

Identifying Optimal Temperature

The optimal temperature for the formation of ether from ethanol is around \(413 \, \text{K}\). At lower temperatures, ether is not formed efficiently, and at higher temperatures, alkene may form instead.

Selecting the Correct Option

Based on the optimal temperature conditions for ether formation from ethanol using \(\mathrm{H}_{2}\mathrm{SO}_{4}\), select the temperature of \(413 \, \text{K}\) as it best aligns with the desired reaction conditions.

Key concepts

Ethanol dehydration

Dehydration is a process where water molecules are removed from a compound. In the context of ethanol dehydration, the aim is to remove water from ethanol to form ether, specifically diethyl ether, by using a strong acid. Ethanol (C₂H₅OH) acts as the substrate that is dehydrated. The reaction involves the use of a catalyst, which in industrial and laboratory settings is often concentrated sulfuric acid (H₂SO₄). This catalyst helps in breaking the O-H bond.

Here's a simplified look at the dehydration process of ethanol:

• The ethanol molecule reacts with hydrogen ions (H⁺) provided by the sulfuric acid.
• This interaction creates an oxonium ion (C₂H₅OH₂⁺), which makes the O-H bond ready to release water.
• The formation of the oxonium ion is key to facilitating the breaking of the bond in a controlled manner, allowing the formation of an ether linkage between ethanol molecules.

Dehydration to produce ether can be rather selective based on temperature, as we'll soon explore. Nevertheless, ethanol dehydration is a foundational chemical reaction in organic chemistry.

Optimal temperature for ether synthesis

The temperature plays a pivotal role in ensuring the desired product, diethyl ether, during the dehydration of ethanol. The optimal temperature for synthesizing ether from ethanol is approximately 413 K. Let's break down why temperature matters so much.

At lower temperatures, insufficient energy leads to ineffective dehydration. The molecules do not have enough kinetic energy to overcome the activation energy barrier needed to form the ether linkage. As a result, the reaction proceeds slowly or not at all.

On the other hand, if the temperature is significantly increased beyond 413 K, the likelihood of forming unwanted side products like ethylene (an alkene) increases. This occurs because higher kinetic energy can disrupt the selective dehydration process, leading to elimination reactions instead.

• At high temperatures, ethanol may undergo a competing elimination reaction producing alkenes instead of ether.
• Hence maintaining this optimal temperature ensures a higher yield of ether while minimizing by-products.

Sulfuric acid as dehydrating agent

Sulfuric acid (H₂SO₄) is the chemical workhorse in the dehydration of ethanol to produce ether. Its role as a dehydrating agent is facilitated by its ability to donate hydrogen ions (H⁺), thereby making it a very potent proton donor.

• Sulfuric acid's strong acidic nature allows it to protonate the hydroxyl group (-OH) of ethanol.
• This makes the oxygen a good leaving group in the form of water, advancing the formation of ether by creating the oxonium intermediate.

One might ask, why use sulfuric acid and not another acid? The answer lies in the effectiveness and accessibility of sulfuric acid:

• Sulfuric acid is not only strong but also forms a non-volatile conjugate base which is beneficial in maintaining the reaction conditions stable.
• It has a high boiling point, allowing it to operate consistently at high reaction temperatures without evaporating.

Its dual role, both as a catalyst and dehydrating agent, makes sulfuric acid ideal for the industrial synthesis of diethyl ether from ethanol.