By which of the following reactions can methylcyanide be prepared?

Options

A. `CH_(3)Broverset(KCN)underset(DMF)rarr`
B. `CH_(3)NH_(2) +CHCI_(3) overset(KOH)rarr`
C. `CH_(3)-CH=N-OH overset(P_(2)O_(5))underset(Delta)rarr`
D. `CH_(3)-overset(O)overset(||)(C)-NH_(2)overset(P_(4)O_(10))underset(Delta)rarr`

Answer

To prepare methyl cyanide (also known as acetonitrile, CH3CN), we can consider various reactions. Let's analyze the reactions step-by-step to determine which of them can yield methyl cyanide.

### Step-by-Step Solution:

1. **Understanding Methyl Cyanide**:
- Methyl cyanide has the structure CH3CN, where CH3 represents the methyl group and CN represents the cyanide group (C≡N).

2. **Analyzing the Given Reactions**:
- We need to identify which reactions can lead to the formation of CH3CN.

3. **Reaction with Alkyl Halides and Cyanide Ion**:
- If we react an alkyl halide (like bromoethane, CH3Br) with a cyanide ion (CN⁻), we can perform a nucleophilic substitution reaction.
- The reaction would look like this:
\[ CH3Br + CN^- \rightarrow CH3CN + Br^- \]
- This reaction is valid and will produce methyl cyanide.

4. **Using Chloroform and Ammonia**:
- Another method involves using chloroform (CHCl3) and ammonia (NH3) in the presence of a base. This reaction can lead to the formation of cyanide.
- The reaction proceeds as follows:
\[ CHCl3 + NH3 \rightarrow CH3CN + HCl + H2O \]
- This reaction is also valid for the formation of methyl cyanide.

5. **Dehydration of Amides**:
- If we take an amide (like acetamide, CH3CONH2) and treat it with a dehydrating agent (like P2O5), it can lead to the formation of methyl cyanide:
\[ CH3CONH2 \xrightarrow{P2O5} CH3CN + H2O \]
- This reaction is also valid.

6. **Using Phosphorus Oxychloride (P4O10)**:
- Similarly, treating an amide with phosphorus oxychloride (P4O10) can also yield methyl cyanide:
\[ CH3CONH2 \xrightarrow{P4O10} CH3CN + HCl + H2O \]
- This reaction is also valid.

### Conclusion:
From the analysis, we can conclude that methyl cyanide can be prepared by:
- Reaction of an alkyl halide with cyanide ion.
- Reaction of chloroform with ammonia.
- Dehydration of acetamide using P2O5 or P4O10.

### Valid Reactions:
- A: Alkyl Halide + CN⁻ → Methyl Cyanide
- B: Chloroform + NH3 → Methyl Cyanide
- C: Acetamide + P2O5 → Methyl Cyanide
- D: Acetamide + P4O10 → Methyl Cyanide