1. Definition of Green Chemistry

Green chemistry is the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances throughout their life cycle.

• It is also called sustainable chemistry.

• The concept was developed and popularised by Paul T. Anastas and John C. Warner.

• The main objective is to prevent pollution at its source rather than control it after formation.

• It promotes safer chemicals, renewable feedstocks, energy efficiency and waste minimisation.

• It integrates chemistry with environmental protection, human health and sustainable development.

2. Objectives of Green Chemistry

• Minimise or eliminate hazardous chemical substances.

• Prevent waste generation at the source.

• Improve atom economy and reaction efficiency.

• Reduce energy consumption during chemical manufacturing.

• Replace toxic solvents with safer alternatives.

• Promote renewable raw materials.

• Develop biodegradable and environmentally benign products.

• Reduce greenhouse gas emissions and industrial pollution.

• Improve occupational safety and public health.

• Support sustainable industrial development and a circular economy.

3. Twelve Principles of Green Chemistry

The twelve principles were formulated by Anastas and Warner in 1998.

1. Prevention of Waste

Preventing waste is better than treating or cleaning it up after it has been generated. Processes should minimise by-products and unwanted materials.

2. Atom Economy

Synthetic methods should maximise the incorporation of all reactant atoms into the desired final product.

\[ \text{Atom economy}= \frac{\text{Molar mass of desired product}} {\text{Total molar mass of reactants}}\times100 \]

3. Less Hazardous Chemical Syntheses

Synthetic processes should use and generate substances with little or no toxicity to humans and the environment.

4. Designing Safer Chemicals

Chemical products should perform their intended function while minimising toxicity and other harmful effects.

5. Safer Solvents and Auxiliaries

Avoid auxiliary substances where possible. When necessary, select safer solvents and separation agents, such as water or suitable bio-based solvents.

6. Energy Efficiency

Minimise energy requirements. Conduct reactions at ambient temperature and pressure wherever technically feasible.

7. Use of Renewable Feedstocks

Prefer renewable raw materials, such as biomass, over depleting resources when technically and economically practicable.

8. Reduce Derivatives

Avoid unnecessary protection, deprotection and temporary modification steps because they consume reagents and produce waste.

9. Catalysis

Catalytic reagents are generally preferable to stoichiometric reagents because small quantities of catalysts can promote repeated reaction cycles and reduce waste.

10. Design for Degradation

Chemical products should break down into harmless substances after use and should not persist unnecessarily in the environment.

11. Real-Time Analysis for Pollution Prevention

Develop analytical methods for monitoring processes in real time to prevent hazardous substances and unwanted by-products from forming.

12. Inherently Safer Chemistry for Accident Prevention

Choose substances and process conditions that minimise the risks of fires, explosions, leaks and accidental releases.