By a proper choice of reagent, both symmetrical and unsymmetrical ethers can by prepared by williamson synthesis which involves the reaction between an alkyl halide and an alkoxide ion. The reverse process involving the cleavage of etehrs to give back the original alkyl halide and the alcohol can be carried out by heating the ether with HI at 373K.
Q. Which of the following ethers is not cleaved by HI?

Options

A. Dicyclohexyl ether
B. Phenetole
C. di-tert-butyl ether
D. Diphenyl ether

Explanation

To determine which ether is not cleaved by HI, we need to analyze the ethers provided in the question. The cleavage of ethers by HI involves breaking the bond between the oxygen and the carbon atoms.

### Step-by-Step Solution:

1. **Understanding Ether Cleavage**: Ethers can be cleaved by hydrogen iodide (HI) at elevated temperatures (373 K). The cleavage results in the formation of an alkyl halide and an alcohol.

2. **Identifying the Ethers**: The question likely provides multiple ethers to choose from. Common ethers include:
- Phenyl ether (or diphenyl ether)
- Tertiary butyl ether
- Ethyl ether
- Simple symmetrical ethers

3. **Analyzing Each Ether**:
- **Phenyl Ether (Diphenyl Ether)**: This ether has two phenyl groups attached to the oxygen. The bond between the carbon atoms of the phenyl groups and the oxygen is quite strong due to resonance stabilization. Therefore, diphenyl ether is resistant to cleavage by HI.
- **Tertiary Butyl Ether**: This ether can be cleaved by HI, yielding tertiary butanol and tertiary butyl iodide.
- **Ethyl Ether**: This ether can also be cleaved by HI to yield ethyl iodide and alcohol.
- **Symmetrical Ethers**: These can generally be cleaved by HI unless they have sterically hindered groups.

4. **Conclusion**: Among the ethers analyzed, diphenyl ether is the one that is not cleaved by HI due to the strength of the carbon-oxygen bond in the presence of the phenyl groups.

### Final Answer:
The ether that is not cleaved by HI is **Diphenyl Ether**.