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 need to identify the correct reagent that facilitates this transformation. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify Glycol
- Glycol commonly refers to ethylene glycol, which has the chemical formula C2H6O2 or HO-CH2-CH2-OH.

### Step 2: Understand the Reaction
- The question states that glycol (ethylene glycol) forms diethylene glycol upon heating. Diethylene glycol has the formula C4H10O3 or HO-CH2-CH2-O-CH2-CH2-OH.

### Step 3: Identify the Reagent
- To convert ethylene glycol to diethylene glycol, a dehydration reaction is required. This means that we need a reagent that can remove a water molecule (H2O) from the glycol to facilitate the formation of the ether linkage in diethylene glycol.

### Step 4: Choose the Correct Reagent
- The reagent that is commonly used for dehydration reactions in organic chemistry is concentrated sulfuric acid (H2SO4) or phosphoric acid (H3PO4). In this case, the question specifies that the reaction occurs with concentrated H3PO4.

### Step 5: Write the Reaction
- The reaction can be summarized as follows:
\[ 2 \, \text{HO-CH}_2\text{-CH}_2\text{-OH} \xrightarrow{\text{H}_3\text{PO}_4} \text{HO-CH}_2\text{-CH}_2\text{-O-CH}_2\text{-CH}_2\text{-OH} + \text{H}_2\text{O} \]

### Conclusion
- Therefore, the correct answer to the question is that glycol forms diethylene glycol on heating with concentrated phosphoric acid (H3PO4).

### Final Answer:
- Glycol forms diethylene glycol on heating with concentrated H3PO4.

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