Green Chemistry

• Definition :

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• In simple terms,Green chemistry is maintainging environmentally sound practices through the lifecycle of a chemical product (design , manufacture, use and ultimate disposal) and processes.

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• It is also known as sustainable chemistry.

IUPAC Definitions of Green Chemistry�

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• Design of chemical product and process that reduce or eliminate the use or generation of substance hazardous to humans, animal ,palnts and the environment.

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• In the 1990 paul Anastas, who was the chief of the industrial chemistry branch at us environmental protection agencey, moved forward the concept of green chemistry.

Significance of Green Chemistry

REDUCING

RISK &

HAZARD

COST

ENERGY

NON-

RENEWABLE

WASTEWA

MATERIAL

Principles

• Prevention of waste water/ by product
• Atom economy
• Less hazardous synthesis.
• Design safer chemicals
• Safer solvent & Auxilliaries.
• Use Renewable feedstock.
• Design for energy efficinecy.
• Use of catalyst
• Design for degradation.
• Reduce derivatives
• Real time analysis
• Inherently bengin chemistry for accident prevention

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1.Prevention

• It is better prevent waste than to treat and clean up waste after it has been created.

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• Common practice dump waste on land or in water or released in air ,soil, water and air pollution.

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• Compulsion to have waste treatment thus the cost of process increased considereably.

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• It is best to carry out synthesis so that formation of waste is minimum or absent.

2.Atom Economy

• Most of the organic reaction release undesired products along with the useful product of the reaction .

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• A reaction is considered green if there is maximum incorporation of starting material in the final product.

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• Green chemistry: New process should be designed such that the most of the starting material gets converted into product this called as maximising atom economy.

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3.Designing safer chemicals.

• Dyes, paints, cosmetices ,medicine,should be safe to used.

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• Thalidomide drug used during pregnancy to reduce the effect of nausea and vomiting in birth defects in children born to those women ,subsequently it was banned.

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• The use of toxic insecticides like DDT, is curtailed and alternatively biological pesticides are move in use

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• Chemical products should be designed to do their job with minimun harm to people or the environment.

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• Thus green chemistry emphasizes to design chemical product to be fully effective,yet have little or no toxicity.

4. Safer solvent

• try not to use unnecessary chemicals.

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• If needed they should not be harmful to the environment.

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• Avoid using solvents, separation agent, or they auxiliary chemicals.

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• If asolvent is necessary,water is a good medium as well as certain eco-friendly solvents like ionic liquids,liq CO2

e.g. for dry cleaning the fabrics,toxic solvent like per chloro ethylene is replaced during recent years by liquid CO2

5.Less Hazardous chemical synthesis:-

• Production methods should be designed to make substances that are less toxic to people or the enviornment

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• The starting material selected should be least toxic.

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• The reactions, in which intermediates or reagents or products are toxic, should not be followed

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• Instead alternative pathways should be used for synthesis.

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Hazardous chemicals include (for example):bromine, chlorine, phosgene, dimethyl sulphate, formaldehyde, hydrogen fluoride, hydrogen chloride, benzene, sodium azide and radioactive chemicals.

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6. Designs for energy efficiency:-

• The energy needed to carryout a reaction should be minimized to reduce enviornmental & economic impact.

If possible, process should be carried at ambient temperatures and pressures

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• Use of catalysts and by stopping the use of fossile/ gaseous fuels which release solid or gaseous pollutants.

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• Substitutes like microwave radiations and ultra sound, fermentation process require very less energy.

7.Use of Renewable Feedstock

• A raw material or feedstock should be renewable wherever possible

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• Biodiesel: a cleaner, renewable energy source

Biodiesel is renewable energy made from feedstock oil (soy,canola,palm) or animal fat (poultry).It can be used in transporatation ,heating,& power generation

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• Pyrolysis oils are made from waste wood,agricultural waste and non-food energy crop.
• They are used to produce high-value materials like solvents, detergents to plastics and fibers.
• They are the cheapest of the liqiud fuels,derived from biomass, that are available today.

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8.Reduce Derivatives:-

• A commonly used technique in oraganic synthesis is use of protecting and deprotecting of groups for selective conversions
• The use of derivatives .....increases the steps of the process.....additional reagents are required.....generates more waste products to avoid these effects
• Alternative reagents are to be used which are more selective.

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• Thus as far as possiable use of protecting groups should be avoided

9. Catalysis

• Reactions that are catalyzed are more efficient than uncatalyzed reactions.

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• Catalyst carry out reactions without being consumed or incorporated in the final product.

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• Starting material is fully utilized; Minimum waste

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• Catalysts are used in small amounts and carry out a single reaction many times.It can carry out thousands of transformations without being exhausted.

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• Selective in action.

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• In recent years many processes are been developed which use non-toxic recoverable catalysts and also biocatalysis

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10.Designs for Degradations:

• Products synthesized should be biodegradable, they should not accumulate in the environment, such chemicals remain in the environment in the same form or taken by plants and animals and accumulate in their system

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• Whenever chemical is designed make sure that it is biodegradable.

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• The packaging material such as plastics or polystyrene are non-biodegradable and cause solid waste

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• The alternative to this is the biodegradable plastics containing cellulose and the packing pellets made up of starch are used

11.Real-time analysis for pollution prevention:

• E.g. Preparation of ethylene glycol, in which if reaction conditions if not monitored perfectly, toxic substances are produced at higher temperature.

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• One needto have accurate and relate sensors, monitors, analytical techniques to find the hazards that are present in the process.

12. Inherently safer Chemistry for Accident prevention:

• Recyling of solvents increases the potential for chemical accidents
• Aprocess must balance the accident prevention with adesire for preventing pollution.Instead of volatile solvent,solid or low vapour pressure substance can be used.

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• Substances used in chemical process should be chosen to minimize the risk of the chemical accidents, including explosions and fires.

Green Reagents

The most significant features of this process are:-

• low-cost and widely available raw materials with low toxicity

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• High production rates

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• Non-toxic and easy disposable by-products (carbon dioxide &water)

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• High quality product

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• Biodegradability >90% at 28 days.

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• DMC is a green solvent and ragent since it incorporates several fundamental aspects of green chemistry.

1.Properties:-

• Dimethyl carbonate appears as a clear,colorless liquid with a pleasant odor with boiling point 90°C & freezes at 3°C.

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• It is denser than water and slightly soluble in water.Its vapors are heavier than air.

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• It is used to make other chemicals and as a special purpose solvent.

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• DMCis awell-known non-toxic reagent showing three main green chemistry features as compared to other carboxylating agents like hazardous phosgene and methyl halides, etc

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• DMC does not produce inorganic salts in either acylation or alkylation

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• Nu^- + CH₃OCOOH₃ ⇌ NuCOOH₃ + CH₃O^- (1)

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• Nu^- + CH₃OCOOH₃ 🡪 NuCH₃ + CH₃OCOO ^– (2)

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• CH₃OCOO ^– 🡪 CH₃O^- + CO ₂ (3)

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• In reaction(3) Methyl Carbonate decomposes, the base is restored and can be used in truly catalytic amounts. This features allows utilization of continuous-flow procedures and contiuously stirred tank reactor.

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• Since reaction 1 an equilibrium and reaction 2 is not, the product of the process can be controlled, temperature being the key factor.

2.Aplications:-

• Fuels and fuel additives

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• Functional fluids (open systems)

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• Paint additives and coating additives

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• Plasticizers

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• Solvents (for cleaning and degreasing)

Supercritical carbon dioxide:-

• Triple point for any system is specific temperature and pressure at which all the phases namely solid,liquid and gaseous occur simultaneously.
• Critical point for any system is that temperature at which no phase boundaries exist. Supercritical(SC) fluids are those which temperature and pressure above critical.

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Properties:-

• Non toxic

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• Non-immflammable

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• Low critical parameter

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• Insert to most material

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• High dissolving power

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• Relatively inexpensive

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• Enivornmentally non-hazardous

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• Good transport and storage property

Applications:-

• Refrigerator
• In nano-electronics
• For dry cleaning
• Supercritical drying
• Biodiesel production
• Supercritical water oxidation
• Supercritical water gasification
• Supercritical fluid extraction
• Supercritical fluid deposition
• Supercritical fluid decomposition
• Supercritical fluid chromatography
• Supercritical fluid in power generation
• Generation of pharmaceutical co-crystals

Biopolymers

• Biopolymers in nature are produced by a range of microoragnisms and plants

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• Biopolymers produced by microoragnisms require specific nutrients and controlled environmental conditions.

1.Synthesis of nanomaterials

• The focus for the synthesis protocol has shifted from physical and chemical processes towards “green” chemistry and bioprocesses

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• In common synthesis methods, the reducing agent used which include organic solvents and toxic-reducing agent like hydrazine, N-dimethylformamide and sodium borohydride are highly toxic for enviornment

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• Biopolymers have been extensively used as crapping and reducing agent for synthesis of various nanoparticals

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• Biopolymers like chitosan, heprain, soulable starch, cellulose, gelatin, polyvinyl alchol(PVA), PVP and so on can be used to replace various toxic reagents in synthesizing different nanoparticles

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2.Biomedical applications

• In recent year,biopolymers materials have aroused great interest because of their biomedical applications,such as those in tissue engineering, pharmaceutical carriers and medical devices

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• A coomon biopolymers, gelatin, was widely applied in medicine for dressing wounds, as an adhesive and so on.

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3.Food industry

• Biopolymers are currently used in food coatings,food packaging materials and encapsulation matrices for funcitonal foods

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• The most commercially viable materials in food packaging are certain biodegradable polyesters and thermoplasts like starch, PLA, Polyhydroxyalkanotaes (PHA) and so on, which can be processed by conventional equipments.

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• PLA is particular intreset in food packaging, due to its excellent transparency and relatively good water resistance.

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• Lysozyme is one of the most frequently used in antimicrobial enzymes in packaging materials since it is a nutrally occuring enzymes.

4.Water purification

• A relatively new biopolymers, chitosan shows superior performance where may conventional polymers fail. Chitosan removes metals(arsenic, lead, etc.) from water by forming chelates.

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• Porous GO-biopolymers gels can efficiently removes cationic dyes and heavy metal ions from wastewater.

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• Nano-fibers membranes can improve the water-filtration process without adversely affecting environment.