greenchemistry

Green Chemistry focuses on : • Reduction, recycling and/or eliminating toxic substances • Finding creative, alternative routes to minimize impact on the environment • More eco-friendly green alternative toconventional chemistry practices • Provides sustainable development, sustainable business and sustainable living practices

Twelve Principles of Green Chemistry

1. Prevent Waste :

• Synthesis only targeted product with minimum or no by products/waste
• If waste is produced , it involves cost and time to treat and safely dispose it, as a result production cost increases

2. Atom Economy: Synthetic methods should be

• designed to maximize the incorporation of all materials used into the final product
• The chemical processes should have maximum product yield
• Atom economy can be calculated using the relation
• % Atom Economy = (FW of atoms utilized/FW of all reactants) X 100

Atom Economy in a Substitution Reaction - moderate Atom Economy in Elimination Reactions - low Atom Economy in Addition Reactions -100% Atom Economy in Rearrangement Reactions -100%

For a green synthesis atom economy must be maximum (100%)

3. Safer Synthesis:

• The synthetic processes should be
  • designed so as to minimize or prevent the production of hazardous substances
• Necessary safety precautions have to be taken while processing to protect human health and environment
• eg: Polyurethane is manufactured conventionally using and alcohol. However, isocyanate is produced using phosgene, a toxic gas
• The alternative method by green synthesis of polyurethane eliminates the use of phosgene and uses CO2

4. Safe Products : Chemical products should be designed

• to preserve efficacy of function while reducing toxicity
• Products should not have any side effects on the people using it and on the environment
• It is envisaged to produce the chemical products specially those being used in cosmetics, pharmaceuticals, etc.

5. Design Benign Chemicals :

• Use safer solvents and reaction conditions
• Avoid using solvents, separation agents, or other auxiliary chemicals
• If these chemicals are necessary, use innocuous chemicals
• Chemical syntheses are assisted by solvent medium:
• recommended to use alternative solvents , greener in nature such as aqueous medium, liquid carbon-dioxide, ionic liquids(N-alkyl pyridinium cation with BF4-), or solvent free systems
• Avoid harmful solvents like chloroform, pyridine which are known to cause health hazard, are carcinogenic to human beings and animals or cause severe damage to environment

6. Design for Energy efficiency :

Chemical processes are to be designed in such a way that they are less energy intensive

• reactions occurring at mild conditions
• require less time to complete

For this purpose it is worthwhile to utilize

• Bio-catalyst, homogeneous and heterogeneous catalyst which reduces the energy of activation
• Modern techniques such as solvent free synthesis, supercritical fluid systems, microwave irradiation, and ultrasound

7. Use of renewable feedstock :

• Raw material or feedstock used as starting material should be renewable rather than depleting wherever technically and economically possible
• Use of renewable feedstock such as biomass and agricultural wastes are strongly recommended rather than using non-renewable resources such as coal, petroleum-based raw materials, etc.

8. Reduce Derivatives:

• Avoid unnecessary derivatization
• temporary modification should be avoided whenever possible as they generate waste
• the atom efficiency is reduced as the protective group is not incorporated in the final product e.g: blocking group, protection/ deprotection

9. Catalysis:

• Use catalytic reactions, as catalysts
• Speed up the reaction can be recycled and are highly selective
• less energy consumption during reaction
• obtaining high yield of product of high purity

Unlike stiochiometric reactions which are energy intensive require excessive reagents

10. Design for Degradation :

• Design chemicals and products to degrade after use to innocuous substances after use so that they do not accumulate in the environment
• Especially applicable to:
• insecticides
• pesticides
• polymers which tend to persist in the environment and are known to cause bioaccumulations

11. Pollution Prevention :

• Real-time analysis (quality control)
• Continuously monitor and control the formation of hazardous substances
• Any unreacted reactant can be recycled in order to minimize the use of chemicals

12. Accident Prevention :

• Minimize the potential for accidents
• Chemicals chosen for processes should be such which minimise accidents in the form of fires, explosions, and toxic releases to the environment
• Manufacturing plants should be well equipped with safety mechanisms
• The Bhopal gas tragedy is one of the worst industrial disasters

Green chemistry is a set of principles which emphasises on

• environmentally benign chemical synthesis with a view to devise pathways for the prevention of pollution.
• bringing a paradigm shift in chemical processing to achieve sustainable development.