Question

When ethanol is treated with sulphuric acid at \(413\ K\), the reaction involved in it is:

• A. \(S_N2\)
• B. \(S_N1\)
• C. Addition
• D. Elimination

Hint:

Ethanol with concentrated \(H_2SO_4\): \[ 413\ K \rightarrow \text{Diethyl ether} \quad (S_N2) \] \[ 443\ K \rightarrow \text{Ethene} \quad (\text{Elimination}) \] Temperature determines the major product.

Answer 1

The Correct Option is A

Step 1: Recall the reaction of ethanol with concentrated sulphuric acid at \(413\ K\).
At \(413\ K\), ethanol reacts with concentrated sulphuric acid to form diethyl ether: \[ 2C_2H_5OH \xrightarrow[\ 413K\ ]{\text{Conc. }H_2SO_4} C_2H_5OC_2H_5+H_2O \]

Step 2: Understand the mechanism.
First, ethanol gets protonated: \[ C_2H_5OH+H^+ \rightarrow C_2H_5OH_2^+ \] A second ethanol molecule then attacks the ethyl carbon and displaces water.
This attack occurs in a single step through backside attack, characteristic of an \[ S_N2 \] mechanism.

Step 3: Why not \(S_N1\)?
Formation of a primary carbocation \[ C_2H_5^+ \] is highly unstable.
Therefore, the reaction does not proceed through an \(S_N1\) pathway.

Step 4: Why not elimination?
Elimination occurs predominantly at higher temperature (\(443\ K\)), producing ethene: \[ C_2H_5OH \xrightarrow[\ 443K\ ]{\text{Conc. }H_2SO_4} CH_2=CH_2+H_2O \] Since the temperature is \(413\ K\), ether formation is favored.

Step 5: Final conclusion.
Therefore, the reaction involved is \[ \boxed{S_N2} \] Hence, the correct option is \[ \boxed{(1)} \]