1. Green Chemistry
Chapter 5

2. DEFINITION OF GREEN OR SUSTAINABLE CHEMISTRY
An approach to design, manufacture and use of chemical products to deliberately reduce or eliminate the chemical hazards and protect the environment.

3. Basic Principles of Green Chemistry
12 principles advocated by Dr. Paul Anastas and Dr. John Warner.
Prevention
Atomic Economy
Less Hazardous Chemical Synthesis
Designing Safer Chemicals
Safer Solvents and Auxiliaries
Design for energy efficiency

4. Use of Renewable Feedstocks
Reduce Derivatives
Catalysis
Design for Degradation
Real –Time analysis for Pollution prevention
Essentially Safer Chemistry for Accident Prevention

5. 1. Prevention
It is better to prevent waste than to treat or clean up waste after created it.
So, waste prevention is better than waste cleanup.

6. Environmental Disasters
Love Canal
In Niagara Falls, NY a chemical and plastics company had used an old canal bed as a chemical dump from 1930s to 1950s. The land was then used for a new school and housing track. The chemicals leaked through a clay cap that sealed the dump. It was contaminated with at least 82 chemicals (benzene, chlorinated hydrocarbons, dioxin). Health effects of the people living there included: high birth defect incidence and seizure-inducing nervous disease among the children.

7. Cuyahoga River – Cleveland, Ohio
There were many things being dumped in the river such as: gasoline, oil, paint, and metals. The river was called "a rainbow of many different colors".
Some river! Chocolate-brown, oily, bubbling with subsurface gases, it oozes rather than flows. "Anyone who falls into the Cuyahoga does not drown," Cleveland's citizens joke grimly. "He decays." Time Magazine, August 1969

8. 2. Atomic Economy
Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

9. Atom Economy Atom Economy
% AE = (FW of atoms utilized/FW of all reactants) X 100
Balanced Equations
Focuses on the reagents
Stoichiometry?
How efficient is the reaction in practice?
Solvents?
Energy?

10. Atom Economy Balanced chemical reaction of the epoxidation of styrene
Assume 100% yield.
100% of the desired epoxide product is recovered.
100% formation of the co-product: m- chlorobenzoic acid
A.E. of this reaction is 23%.
77% of the products are waste.

11. 3. Less Hazardous Chemical Synthesis
Synthetic routes should be designed in such a way that, it generates and uses substances that possess no or little toxicity to human health and the environment.

12. Preparation of acetanilide
Conventional method:
Green Procedure:
Non-green components : CH2Cl2 , Pyridine
Not atom – economic : 1 mole of acetic acid unused.

13. Nitration of phenol Electrophilic Aromatic Substitution reaction
Conventional procedure:
Green Procedure:
Non-green component

14. Bromination of Acetanilide
Conventional procedure:
Green Method
Non-green component : Liquid molecular bromine

15. 4. Designing Safer Chemicals
New chemical should be design with great effectiveness and new approaches to minimize the toxicity and harmless to the environment.

16. 5. Safer Solvents and Auxiliaries
The auxiliary substances (Inorganic and organic solvents) should be replaced by safer and eco-friendly green solvents like IL, supercritical CO2 fluid, and Supercritical water.
Promote solvent free systems i.e adsorbents like clays, zeolites, silica, and alumina.

17. Safer solvents: Supercritical fluids
A SCF is defined as a substance above its critical temperature (TC) and critical pressure (PC). The critical point represents the highest temperature and pressure at which the substance can exist as a vapor and liquid in equilibrium.

18. Ionic Liquids (Ils) Liquid at room temperature and below. Non-volatile
Negligible vapour pressure
Can be recycled
High thermal stability to 200 oC or higher
First Room temperature ionic liquid (RTIL) : Ethylammonium Nitrate [EtNH3 ]+[NO3]- was synthesized by Paul Walden (1914) using neutralization method.

19. Supercritical CO2 fluid
Have low viscosity
No surface tension
Low toxicity
Non-flammability
Easily evaporated leaving no residue
Can dissolve wide range of chemicals
Used in fragrance compounds

20. Supercritical water Water become supercritical at 3740C and 218 atm.
Use as a green solvent for many synthetic reactions.

21. 6. Design for Energy Efficiency
Energy requirements should be minimized.
Process should be designed to occur at ambient conditions.
Microwave irradiation, Sonication reaction or biological processes.
- Microwave irradiation: Beckmann rearrangement of oximes without acid catalyst.
-Sonochemistry (Ultrasound Energy): Ullmann’s coupling.

22. 7. Use of Renewable Feedstocks
A raw material or feedstock should be renewable rather than depleting whenever technically and economically practical.

23. Biomaterials [Carbohydrates, Proteins, Lipids]
Highly Functionalized Molecules
Petroleum Products [Hydrocarbons]
Singly Functionalized Compounds [Olefins, Alkylchlorides]
Highly Functionalized Molecules

24. 8. Reduce Derivatives
Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible.

25. 9. Catalysis
Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

26. 10. Design for Degradation
Chemical products should be designed so that at the end of their function they do not persist in the environment and instead break down into innocuous degradation products.

27. Chlorofluorocarbons (CFCs)
Examples
Chlorofluorocarbons (CFCs)
Do not break down, persist in atmosphere and contribute to destruction of ozone layer
DDT
Bioaccumulate and cause thinning of egg shells

28. 11. Real-time Analysis for Pollution Prevention
Analytical methodologies need to be further developed to allow for real-time in-process monitoring and control prior to the formation of hazardous substances.

29. Real time analysis for a chemist is the process of “checking the progress of chemical reactions as it happens.”
Knowing when your product is “done” can save a lot of waste, time and energy!

30. Analyzing a Reaction
What do you need to know, how do you get this information and how long does it take to get it?

31. 12. Inherently Safer Chemistry for Accident Prevention
Substance and the form of a substance used in a chemical process should be chosen so as to minimize the potential for chemical accidents, including releases, explosions, and fires.

32. Cyanide!
Phosgene!

33. Tragedy in Bhopal, India - 1984
What happened?
Methyl isocyanate – used to make pesticides was being stored in large quantities on-site at the plant
Methyl isocyanate is highly reactive, exothermic molecule
Most safety systems either failed or were inoperative
Water was released into the tank holding the methyl isocyanate
The reaction occurred and the methyl isocyanate rapidly boiled producing large quantities of toxic gas.

34. Conclusion
Green chemistry Not a solution to all environmental problems But the most fundamental approach to preventing pollution.

35. Thank you