What is Z in the following reactions ?
`BCl_3 + H_2 underset(450^@ C)overset(Cu-Al)to X + HCl`
`X overset("methylation")to Z`

Options

A. `(CH_3)BH_2`
B. `(CH_3)_4 B_2 H_2`
C. `(CH_3)_3 B_2 H_3`
D. `(CH_3)_6 B_2`

Answer

To determine what Z is in the given reactions, we will break down the steps involved in the reactions of BCl3 with H2 and the subsequent methylation of the product.

### Step 1: Identify the Reaction of BCl3 with H2
The first reaction involves boron trichloride (BCl3) reacting with hydrogen gas (H2) in the presence of a catalyst (Cu-Al) at a high temperature (450°C).

**Reaction:**
\[ BCl_3 + H_2 \xrightarrow{450^\circ C, Cu-Al} B_2H_6 + HCl \]

**Explanation:**
When BCl3 reacts with H2, it produces diborane (B2H6) and hydrochloric acid (HCl).

### Step 2: Identify Product X
From the first reaction, we can conclude that the product X is diborane (B2H6).

### Step 3: Methylation of X
The next step involves the methylation of diborane (B2H6). Methylation typically involves the reaction of diborane with methyl chloride (CH3Cl).

**Reaction:**
\[ B_2H_6 + 4 CH_3Cl \rightarrow Z + 4 HCl \]

**Explanation:**
In this reaction, the terminal hydrogen atoms of diborane are replaced by methyl groups from methyl chloride, while the bridge hydrogens remain unchanged.

### Step 4: Identify Product Z
The product Z formed from the methylation of diborane is:
\[ Z = CH_3B_2H_4 \]

This compound is known as dimethyl diborane.

### Final Answer
Thus, the final answer for Z is:
\[ Z = CH_3B_2H_4 \]

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