Reaction involves isocyanate as intermediate product:

Options

A. Curtius rearrangement
B. Lassen rearrangement
C. Schmidt rearrangement
D. Hofmann rearrangement

Answer

To solve the question regarding the reaction that involves isocyanate as an intermediate product, we need to analyze each option provided and determine whether isocyanate is formed as an intermediate in the respective reactions.

### Step-by-Step Solution:

1. **Understanding Isocyanate:**
- Isocyanate is represented as R-N≡C, where R is an organic group. It is formed from the rearrangement of certain compounds.

2. **Analyzing Option A: Rearrangement Reaction:**
- The starting compound is R-C(=O)-N3 (an azide).
- Upon heating, the azide group undergoes rearrangement to form an isocyanate.
- The reaction can be summarized as:
- R-C(=O)-N3 → R-N=C=O (isocyanate)
- **Conclusion:** Option A produces isocyanate as an intermediate.

3. **Analyzing Option B: Lossen Rearrangement:**
- The starting compound is R-C(=O)-OH (an alcohol derivative).
- The reaction involves protonation and rearrangement leading to the formation of an isocyanate.
- The reaction can be summarized as:
- R-C(=O)-OH → R-N=C=O (isocyanate)
- **Conclusion:** Option B also produces isocyanate as an intermediate.

4. **Analyzing Option C: Smith Rearrangement:**
- The starting compound is a ketone reacting with hydrazine (N3H).
- The reaction leads to the formation of an isocyanate through a series of steps.
- The reaction can be summarized as:
- R-C(=O)-R' + N3H → R-N=C=O (isocyanate)
- **Conclusion:** Option C produces isocyanate as an intermediate.

5. **Analyzing Option D: Hoffman Rearrangement:**
- The starting compound is a primary amide (R-C(=O)-NH2).
- The reaction involves bromination and rearrangement to form an isocyanate.
- The reaction can be summarized as:
- R-C(=O)-NH2 + Br2/KOH → R-N=C=O (isocyanate)
- **Conclusion:** Option D also produces isocyanate as an intermediate.

### Final Conclusion:
All options A, B, C, and D produce isocyanate as an intermediate product.