tert-Butyl ethyl ether can't be prepared by which reaction?

Options

A. `"tert"-"Butanol"+"ethanol"overset(H^(+))rarr`
B. `"tert - Butyl bromide"+"sodium ethoxide"rarr`
C. `"Sodium tert - butoxide "+"ethyl bromide"rarr`
D. `"Isobutene "+"ethanol"overset(H^(+))rarr`

Explanation

To determine which reaction cannot be used to prepare tert-butyl ethyl ether, we will analyze each of the provided options step by step.

### Step 1: Understanding the structure of tert-butyl ethyl ether
- Tert-butyl ethyl ether is formed from tert-butyl (C(CH3)3) and ethyl (C2H5) groups connected by an oxygen atom.
- The structure can be represented as:
\[ \text{C(CH}_3\text{)}_3\text{-O-C}_2\text{H}_5 \]

### Step 2: Analyzing the reactions

#### Option A: Tert-butanol + Ethanol
- Tert-butanol (C(CH3)3OH) can undergo dehydration in the presence of an acid catalyst to form tert-butyl ethyl ether.
- The reaction can be represented as:
\[ \text{C(CH}_3\text{)}_3\text{OH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{H}^+} \text{C(CH}_3\text{)}_3\text{-O-C}_2\text{H}_5 + \text{H}_2\text{O} \]
- This reaction is feasible, so this option **can** prepare tert-butyl ethyl ether.

#### Option B: Tert-butyl bromide + Sodium ethoxide
- Tert-butyl bromide (C(CH3)3Br) is a tertiary alkyl halide.
- In Williamson synthesis, a sodium alkoxide reacts with a primary alkyl halide. The reaction with a tertiary alkyl halide is not favorable due to steric hindrance.
- The reaction would lead to elimination rather than substitution:
\[ \text{C(CH}_3\text{)}_3\text{Br} + \text{C}_2\text{H}_5\text{O}^- \rightarrow \text{Elimination product (not ether)} \]
- Therefore, this reaction **cannot** prepare tert-butyl ethyl ether.

#### Option C: Sodium tert-butoxide + Ethyl bromide
- Sodium tert-butoxide (C(CH3)3O^-) is a strong nucleophile.
- Ethyl bromide (C2H5Br) is a primary alkyl halide, which is suitable for Williamson synthesis.
- The reaction can be represented as:
\[ \text{C(CH}_3\text{)}_3\text{O}^- + \text{C}_2\text{H}_5\text{Br} \rightarrow \text{C(CH}_3\text{)}_3\text{-O-C}_2\text{H}_5 + \text{Br}^- \]
- This reaction is feasible, so this option **can** prepare tert-butyl ethyl ether.

#### Option D: Isobutene + Ethanol in acidic medium
- Isobutene (C4H8) can form a tert-butyl cation in the presence of an acid.
- Ethanol can then attack this cation to form tert-butyl ethyl ether:
\[ \text{C}_4\text{H}_8 + \text{C}_2\text{H}_5\text{OH} \rightarrow \text{C(CH}_3\text{)}_3\text{-O-C}_2\text{H}_5 \]
- This reaction is also feasible, so this option **can** prepare tert-butyl ethyl ether.

### Conclusion
The reaction that cannot prepare tert-butyl ethyl ether is:
**Option B: Tert-butyl bromide + Sodium ethoxide.**