Glycol forms diethylene glycol on heating with

Options

A. Anhy, `ZnCl_2`
B. Conc. `H_2SO_4`
C. Anhy. `AlCl_3`
D. `H_3PO_4`

Answer

To solve the question "Glycol forms diethylene glycol on heating with," we can follow these steps:

### Step 1: Identify the reactants
- The question mentions "glycol," which typically refers to ethylene glycol (C2H6O2).
- We need to determine what reagent is required to convert ethylene glycol into diethylene glycol.

### Step 2: Understand the reaction
- Diethylene glycol (C4H10O3) can be formed from ethylene glycol through a process called dehydration, where water is removed from the glycol molecule.
- This reaction typically requires a dehydrating agent.

### Step 3: Identify the dehydrating agent
- A common dehydrating agent used in organic chemistry is concentrated phosphoric acid (H3PO4).
- When ethylene glycol is heated with concentrated phosphoric acid, it loses a water molecule, resulting in the formation of diethylene glycol.

### Step 4: Write the reaction
- The reaction can be represented as follows:
\[ \text{C}_2\text{H}_6\text{O}_2 + \text{H}_3\text{PO}_4 \xrightarrow{\text{heat}} \text{C}_4\text{H}_{10}\text{O}_3 + \text{H}_2\text{O} \]
- Here, ethylene glycol reacts with concentrated phosphoric acid under heat to yield diethylene glycol and water.

### Step 5: Conclusion
- Therefore, the correct answer to the question is that glycol forms diethylene glycol on heating with concentrated phosphoric acid.

### Final Answer:
The correct option is **phosphoric acid**.

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