Which of the following reaction can be used to prepare cyclic ethers ?

Options

A.
B.
C.
D.

Explanation

To determine which reactions can be used to prepare cyclic ethers, we will analyze each of the provided reactions step by step.

### Step 1: Analyze Reaction A
1. **Identify the reactants**: In this reaction, we have an alcohol (OH) and sodium hydroxide (NaOH).
2. **Mechanism**: The hydroxide ion (OH-) from NaOH acts as a base and deprotonates the alcohol, creating a negatively charged oxygen.
3. **Nucleophilic attack**: The negatively charged oxygen can then attack a carbon atom that is part of a leaving group (in this case, a chlorine atom). The chlorine leaves as a chloride ion (Cl-), allowing the formation of a cyclic ether.
4. **Conclusion**: This reaction can indeed form a cyclic ether.

### Step 2: Analyze Reaction B
1. **Identify the reactants**: This reaction also involves an alcohol and sodium hydroxide.
2. **Mechanism**: Similar to Reaction A, the hydroxide ion deprotonates the alcohol. However, in this case, the negatively charged oxygen cannot effectively attack another carbon atom because the leaving group is a hydroxyl group (OH-), which is a poor leaving group.
3. **Conclusion**: This reaction does not lead to the formation of a cyclic ether.

### Step 3: Analyze Reaction C
1. **Identify the reactants**: This reaction involves an alcohol, sulfuric acid (H2SO4), and heat.
2. **Mechanism**: The sulfuric acid protonates the alcohol, making it a better leaving group (water). When water leaves, a carbocation is formed.
3. **Nucleophilic attack**: The oxygen can then attack the carbocation, leading to the formation of a cyclic ether.
4. **Conclusion**: This reaction can successfully form a cyclic ether.

### Step 4: Analyze Reaction D
1. **Identify the reactants**: This reaction involves a bromo-substituted compound and sodium hydride (NaH).
2. **Mechanism**: The hydroxide ion (from NaH) acts as a nucleophile and attacks the carbon bonded to the bromine, leading to a nucleophilic substitution (SN2 reaction).
3. **Conclusion**: This reaction does not form a cyclic ether, as it results in a substitution product instead.

### Final Conclusion
The reactions that can be used to prepare cyclic ethers are:
- **Reaction A**
- **Reaction C**