Green chemistry introduction pdf chemistry

Chemistry

1. GITAM-HYD

2. Chapter 1
Introduction to Green Chemistry
GreenChemistry–IntroductionNeedforgreenchemistry
GoalsofGreenChemistry
Anasta’stwelvePrinciplesofgreenchemistry
Designingagreensynthesis(tools):
1. Starting materials
2. Solvents
3. Catalysts
4. Reagents
5. Process with suitable examples

3. Chemistry brought about medical revolution till about the
middle of twentieth century in which drugs and antibiotics
were discovered. These advances resulted in the average life
expectancy rising from 47 years in 1900 to 75 years in 1990's.
The world's food supply also increased enormously due to
the discovery of hybrid varieties, improved methods of
farming, better seeds, use of insecticides, herbicides and
fertilizers.
The quality of life on earth became much better due to the
discovery of dyes, plastics, cosmetics and other materials.
Soon, the ill effects of chemistry also became pronounced,
main among them being the pollution of land, water and
atmosphere.
This is caused mainly due to the effects of by-products of
chemical industries, which are being discharged into the air,
rivers/oceans and the land.
The hazardous waste released adds to the problem. The use of
toxic reactants and reagents also make the situation worse.
The pollution reached such levels that different governments
made laws to minimiseit. This marked the beginning of Green
Chemistry by the middle of 20th century.
Green chemistry is defined as environmentally benign
chemical synthesis. The synthetic schemes are designed in
such a way that there is least pollution to the environment.
As on today, maximum pollution to the environment is
caused by numerous chemical industries. The cost involved
in disposal of the waste products is also enormous.
Therefore, attempts have been made to design synthesis for
manufacturing processes in such a way that the waste
products are minimum, they have no effect on the
environment and their disposal is convenient.
For carrying out reactions it is necessary that the starting
materials, solvents and catalysts should be carefully
chosen. For
example, use of benzene as a solvent must be avoided at
any cost since it is carcinogenic in nature.
If possible, it is best to carry out reactions in the aqueous
phase. With this view in mind, synthetic methods should be
designed in such a way that the starting materials are
consumed to the maximum extent in the final product.
The reaction should also not generate any toxic by-
products.

4. What is Green Chemistry?
Green chemistry can also be described as
–Sustainable chemistry.
–Chemistry that is benign by design.
–Pollution prevention at the molecular level.
–All of the above.
–Focus on processes and products that reduce or eliminate the use of polluting
substances
• Any synthesis, whether performed in teaching,
laboratories or industries should create none or minimum by-products which
pollute the atmosphere
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5. The Benefits of Green Chemistry
• Economical
• Energy efficient
• Lowers cost of production and regulation
• Less wastes
• Fewer accidents
• Safer products
• Healthier workplaces and communities
• Protects human health and the environment
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6. WHY DO WE NEED GREEN CHEMISTRY?
•Chemistry is undeniably a very prominent part of our daily lives.
• Chemical developments bring new environmental problems and harmful unexpected side effects,
which result in the need for ‘greener’ chemical products. Eg. DDT.
• Green chemistry looks at pollution prevention on the molecular scale
It is an extremely important area of Chemistry due to the importance of Chemistry in our world
today and the implications it can show on our environment.
• The Green Chemistry program supports the invention of more environmentally friendly chemical
processes which reduce or even eliminate the generation of hazardous substances. This program
works very closely with the twelve principles of Green Chemistry.
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7. 12 Principles of Green Chemistry
1.Prevention. It is better to prevent waste than to treat or clean up waste after it is formed.
2. Atom Economy. Synthetic methods should be designed to maximize the incorporation of all materials used in
the process into the final product.
3. Less Hazardous Chemical Synthesis. Whenever practicable, synthetic methodologies should be designed to
use and generate substances that possess little or no toxicity to human health and the
environment.
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8. 4. Designing Safer Chemicals. Chemical products should be designed to preserve efficacy of the function
while reducing toxicity.
5. Safer Solvents and Auxiliaries. The use of auxiliary substances (solvents, separation agents, etc.)
should be made unnecessary whenever possible and, when used, innocuous (harmless)
6. Design for Energy Efficiency. Energy requirements should be recognized for their environmental and
economic impacts and should be minimized. Synthetic methods should be conducted at ambient
temperature and pressure.
7. Use of Renewable Feedstocks. A raw material or feedstock should be renewable rather than depleting
whenever technically and economically practical.
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9. 8. Reduce Derivatives. Unnecessary derivatization(blocking group, protection/deprotection, temporary
modification of physical/chemical processes) should be avoided whenever possible.
9. Catalysis. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
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.
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.
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.
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10. Designing a Green Synthesis:
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To design a synthetic of a target molecule, the starting materials are react with a reagent under
appropriate conditions. Before coming to a finalize the synthetic path, consider all the possible
synthetic routes that can give the desired product.
The same desire product can also be obtained by modifying the conditions. The method of choice
should not use toxic starting materials and should eliminate by-products and wastes.
In that we should Follow some important considerations such as
1.Choice of Starting Materials
2.Choice of Reagents
3.Choice of Catalysts
4.Choice of Solvents

11. GITAM-HYD
Choice of Starting Materials
It is very important to choose the appropriate starting materials. The synthetic pathway will depend
on this. Also consider the hazards that may be faced by the workers (chemists carrying out the
reaction and also the shippers who transport these) handling the starting materials.
At present, most of syntheses materials make use of petrochemicals (made from petroleum),
which are non-renewable. Petroleum refining also requires considerable amounts of energy. It
is therefore important to reduce the use of petrochemicals by using alternative starting
materials, which may be of agriculture all biological origin.
For example, some of the agricultural products such as corn, potatoes, soya and molasses are
transformed through a variety of processes into products like textiles, nylon etc. Some of the
materials that have biological origin (obtained from biomass) are: butadiene, pentane, pentene,
benzene, toluene, xylene, phenolics, aldehydes, resorcinol, acetic acid, peraceticacid, acrylic
acid, methyl aryl ethers, sorbitol, mannitol, glucose, gluconicacid, 5-hydroxymethyl furfural,
furfural, levulinicacid, furan, tetrahydrofuran, furfurylalcohol etc.

12. GITAM-HYD
Choice of Reagents
•Most of the common solvents generally used cause severe hazards. One of the commonly used solvents,
benzene is now known to cause or promote cancer in humans and other animals. Some oftheother
aromatic hydrocarbons, for example toluene could cause brain damage, have adverse effect on speech,
visionandbalance,orcauseliverandkidneyproblems
•All these solvents are widely used because of their excellent solvency properties. These benefits
nevertheless, are coupled with health risks.
•Commonly used halogenated solvents, like methylene chloride, chloroform, per-chloroethyleneand
carbon tetrachloride have long been identified as suspected human carcinogens.
•A versatile solvent, carbon dioxide l is used as liquid CO2 or supercritical CO2 fluid (the states of CO2
most commonly used for solvent use). A gas is normally converted to a liquid state by increasing the
pressure exerted upon it.
•It is ideal to carry out the reaction in aqueous phase if possible. The use of water as a solvent has distinct
advantages
•Another way to carry out the reaction is without the use of solvent (solvent less reactions). One such
reaction comprises those reactions in which the starting materials and the reagents serve as solvents.
•Alternatively, the reactions can be performed in the molten state to ensure proper mixing. There is still
another reaction that can be carried out on solid surfaces such as specialized clays.

13. Examples:
Dimethylcarbonate:Conventionalmethylationreactionsemploymethylhalidesor
methylsulfate.Thetoxicityofthesecompoundsandtheirenvironmental
consequencesrenderthesesynthesessomewhatundesirable.Tundo1•2developeda
methodtomethylateactivemethylenecompoundsselectivelyusing
dimethy1carbonate(DMC)(SchemeI)inwhichnoinorganicsaltsareproduced.
Polymer Supported Reagents:
Polymer Supported Peracid:
These are used for epoxidations of alkenes in good yields
Polymer Supported Chromic Acid:Thepolymer supported chromic acid (AmberlystA-26, HCrO~ form is commercially
available) and has been used to oxidiseprimary and secondary alcohol to carbonyl compounds6 and also oxidizes allylic and
benzylic halides to aldehydes and ketones.
Poly-N-Bromosuccinimide(PNBS): It is an efficient polymer based brominating agent and is used as benzylic and
allylic brominating agent. Thus, cumeneon bromination9 yield a, a, a-tribromocumene. However, bromination
with NBS gives a,, a, a-dibromocumeneand a-bromocumene.