Ethanol can be converted into ethoxyethane (diethyl ether) in the laboratory. Under which conditions is ethanol heated with concentrated H2SO4 to produce ethoxyethane?

Introduction / Context:
The conversion of ethanol to ethoxyethane (diethyl ether) is a classic reaction in organic chemistry that illustrates how reaction conditions can control the product. Concentrated sulfuric acid acts as a catalyst and dehydrating agent, and the temperature at which the reaction is carried out determines whether ether or ethene is formed. This question checks whether you remember the specific temperature and reactant conditions required for ether formation.

Given Data / Assumptions:

• The starting alcohol is ethanol.
• The desired product is ethoxyethane (diethyl ether).
• Concentrated H2SO4 is used in the reaction.
• Different options give different temperatures and relative amounts of ethanol and acid.
• We assume standard textbook conditions for laboratory preparation.

Concept / Approach:
When ethanol is heated with concentrated sulfuric acid at about 413 K (around 140°C) and excess ethanol is present, the major product is diethyl ether formed by intermolecular dehydration of ethanol. At higher temperatures, around 443 K (about 170°C), the same mixture instead undergoes intramolecular dehydration to form ethene. At lower temperatures or room temperature, the reaction does not proceed effectively to ether. Therefore, the correct choice must mention heating excess ethanol with concentrated H2SO4 at approximately 140°C.

Step-by-Step Solution:
Step 1: Recall that ethanol + concentrated H2SO4 at around 140°C leads to the formation of diethyl ether.Step 2: Recognise that "excess ethanol" is important to favour bimolecular ether formation rather than elimination to form ethene.Step 3: Note that at around 170°C (443 K), the major product shifts to ethene, not ethoxyethane.Step 4: Options that mention only room temperature or 273 K correspond to conditions that are too mild to drive the dehydration to ether.Step 5: Compare the options and find that only option a describes heating excess ethanol with concentrated H2SO4 at 140°C.Step 6: Conclude that option a gives the correct conditions for preparing ethoxyethane from ethanol.

Verification / Alternative check:
Textbook mechanisms show that sulfuric acid protonates ethanol to form an ethyl hydrogen sulfate intermediate. A second ethanol molecule can then attack this intermediate to give diethyl ether and regenerate the acid, but this bimolecular step is favoured at moderate temperatures and high ethanol concentration. At higher temperatures, elimination to ethene dominates. Many exam preparation books summarise this by stating: "At 413 K, ethanol plus concentrated H2SO4 gives ether; at 443 K, it gives ethene." This widely repeated rule helps confirm the choice of 140°C with excess ethanol for ether formation.

Why Other Options Are Wrong:
Option b and option c describe treatment with concentrated H2SO4 at room temperature or 273 K, which are not the standard conditions for significant ether formation; the reaction rate would be too low. Option d, heating ethanol with excess concentrated H2SO4 at 443 K, corresponds to a higher temperature where elimination to ethene is favoured over ether formation. Therefore, these alternatives do not match the known conditions for preparing ethoxyethane from ethanol.

Common Pitfalls:
A typical mistake is to remember that "concentrated H2SO4 plus heat" is used but to forget the difference between the two temperature ranges and their corresponding products. Another pitfall is to assume that more heat is always better for completing the reaction, which leads students to choose the higher temperature option that actually produces ethene. To avoid this, memorise the approximate values and link them with the product: around 140°C for ether and around 170°C for ethene.

Final Answer:
Ethanol is converted into ethoxyethane by heating excess ethanol with concentrated H2SO4 at about 140°C.