Green Chemistry

8.1 Concept and 12 Principles

Green chemistry (also called sustainable chemistry) was formalised by Paul Anastas and John Warner in their 1998 book. It is defined as the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.

The 12 Principles of Green Chemistry (simplified for RPSC):

1. Waste Prevention: Better to prevent waste than treat or clean up after.
2. Atom Economy: Design reactions that maximise incorporation of starting materials.
3. Less Hazardous Synthesis: Use and generate substances with little/no toxicity.
4. Safer Chemicals: Products that work but have minimal toxicity.
5. Safer Solvents/Auxiliaries: Avoid auxiliary substances; if used, make them innocuous.
6. Energy Efficiency: Conduct reactions at room temperature/pressure where possible.
7. Renewable Feedstocks: Use renewable raw materials (e.g., plant-based, agricultural waste).
8. Reduce Derivatives: Minimise unnecessary derivatisation steps.
9. Catalysis: Use catalytic reagents (rather than stoichiometric).
10. Biodegradable Design: Design for degradation after use.
11. Real-Time Monitoring: Analytical methods to prevent pollution formation.
12. Accident Prevention: Choose safer forms of substances (solid > liquid > gas for hazardous).

8.2 Green Chemistry in Practice

Supercritical CO₂ as Solvent

Supercritical CO₂ (scCO₂) replaces toxic organic solvents (hexane, chloroform) in extraction and dry-cleaning. CO₂ is non-toxic, non-flammable, and recyclable.

Atom Economy Examples

• Traditional synthesis of organic acid from cymene involves multiple steps; green route via biocatalysis achieves 90%+ atom economy.
• Bhopal Gas Tragedy (1984) as anti-example: MIC (methyl isocyanate) storage could have been avoided by producing it in-situ rather than storing tonnes — a green chemistry principle in hindsight.

Biofuels and Green Feedstocks

• Ethanol from sugarcane waste (bagasse) — India's EBP programme
• Biodiesel from Jatropha, algae — National Biofuel Policy 2018 (revised 2022)
• Green hydrogen (electrolysis using renewable electricity) — India's National Green Hydrogen Mission (approved January 2023, budget Rs 19,744 crore) targets 5 million metric tonnes/year by 2030

India-specific Green Chemistry Initiatives

• CSIR-NCL (National Chemical Laboratory, Pune): Research in green catalysis, biocatalysis, and sustainable materials.
• ACS (American Chemical Society) Green Chemistry Institute India: Collaborations with IITs and CSIR labs.
• BIS (Bureau of Indian Standards): Developing eco-label standards for green chemical products.

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