Which of the following practices will not come under Green chemistry?

Options

A. Use of `CO_2` as solvent instead of `CI_2`
B. Use of `H_2O_2 instead of `CI_2`
C. Synthesis of ethanal from ethane in one step
D. Use of tetrachloroethene as a solvent for dry cleaning

Answer

To determine which of the following practices does not come under green chemistry, we need to evaluate each option based on the principles of green chemistry, which emphasizes the reduction or elimination of hazardous substances, particularly chlorinated compounds.

### Step-by-Step Solution:

1. **Understanding Green Chemistry**:
Green chemistry focuses on designing chemical processes and products that reduce or eliminate the use and generation of hazardous substances. A key principle is to avoid chlorinated compounds due to their potential environmental and health impacts.

2. **Evaluating Each Option**:
- **Option 1: Use of CO2 as solvent instead of Cl2**:
- CO2 is a non-toxic and environmentally friendly solvent. Using CO2 instead of a chlorinated solvent (Cl2) aligns with green chemistry principles.
- **Conclusion**: This practice is part of green chemistry.

- **Option 2: Use of H2O2 instead of Cl2**:
- Hydrogen peroxide (H2O2) is a safer oxidizing agent compared to chlorine (Cl2). It is less harmful and can be used effectively in various chemical reactions.
- **Conclusion**: This practice is also part of green chemistry.

- **Option 3: Synthesis of ethanol from ethane in one step**:
- The synthesis of ethanol from ethane using non-chlorinated reagents (like aqueous KOH and PCC) does not involve chlorinated compounds. This process is efficient and avoids harmful substances.
- **Conclusion**: This practice is part of green chemistry.

- **Option 4: Use of Tetrachloroethane as a solvent for dry cleaning**:
- Tetrachloroethane is a chlorinated solvent, which is harmful and not in line with green chemistry principles. Its use is discouraged due to its toxicity and environmental impact.
- **Conclusion**: This practice does not align with green chemistry.

3. **Final Answer**:
The practice that does not come under green chemistry is **Option 4: Use of Tetrachloroethane as a solvent for dry cleaning**.