Dimethyl ether when heated with exces HI gives :

Options

A. `CH_(3) I and CH_(3) OH`
B. `CH_(3) I and H_(2) O`
C. `C_(2) H_(6) +CH_(3) I and CH_(3) OH`
D. `CH_(3) I and HCHO`

Answer

To solve the question "Dimethyl ether when heated with excess HI gives:", we will follow these steps:

### Step 1: Identify the Reactants
Dimethyl ether has the chemical formula \( CH_3OCH_3 \). When heated with excess hydroiodic acid (HI), we need to analyze the reaction that occurs.

**Hint:** Recognize the structure of dimethyl ether and the components of hydroiodic acid.

### Step 2: Write the Reaction
When dimethyl ether reacts with excess HI, it undergoes cleavage. The reaction can be represented as follows:
\[ CH_3OCH_3 + HI \rightarrow CH_3I + CH_3OH \]

**Hint:** Understand that HI provides iodine and protons, facilitating the breakdown of the ether.

### Step 3: Mechanism of the Reaction
1. The oxygen atom in dimethyl ether has lone pairs that can interact with the proton (H+) from HI.
2. This leads to the formation of a protonated ether (an oxonium ion).
3. The bond between the oxygen and one of the methyl groups breaks, resulting in the formation of methanol (CH3OH) and a methyl carbocation (CH3+).
4. The iodide ion (I-) from HI then attacks the carbocation, forming methyl iodide (CH3I).

**Hint:** Focus on the role of the lone pairs on oxygen and the formation of carbocations.

### Step 4: By-products Formation
Since we have excess HI, the methanol produced can further react with another molecule of HI:
\[ CH_3OH + HI \rightarrow CH_3I + H_2O \]

**Hint:** Consider that excess HI can lead to further reactions with the by-products formed.

### Step 5: Final Products
The overall reaction can be summarized as:
\[ 2 CH_3OCH_3 + 4 HI \rightarrow 2 CH_3I + 2 H_2O \]

Thus, when dimethyl ether is heated with excess HI, the primary products are methyl iodide (CH3I) and water (H2O).

**Final Answer:** Dimethyl ether when heated with excess HI gives methyl iodide (CH3I) and water (H2O).

### Summary of Steps:
1. Identify reactants (dimethyl ether and HI).
2. Write the reaction equation.
3. Explain the reaction mechanism.
4. Consider the formation of by-products.
5. Conclude with the final products.