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GREEN CHEMISTRY

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Chemical

Process

“It is better to prevent waste than to treat or clean

up waste after it is formed”

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CONTENT Introduction Principles Uses Water as solvent Ionic liquids Supercritical fluid Catalysis for green chemistry Solvent free reaction Microwave activation Sonochemistry

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Introduction

Green chemistry, also known as sustainable chemistry, is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances.

Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, and use..

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Introduction

Benefits of green chemistry.

Achievements in green chemistry.

Need for green chemistry.

THE 12 PRINCIPLES OF GREEN CHEMISTRY

 

Prevention

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

 

Atom Economy

Synthetic methods should be designed to maximise the incorporation of all materials used in the process into the final product.

 

Less Hazardous Chemical Synthesis

Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to people or the environment.

 

Designing Safer Chemicals

Chemical products should be designed to effect their desired function while minimising their toxicity.

 

THE 12 PRINCIPLES OF GREEN CHEMISTRY

Use of Renewable FeedstocksA raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.

Reduce Derivatives

Unnecessary derivatization (use of blocking groups, protection/de-protection, and temporary modification of physical/chemical processes) should be minimised or avoided if possible, because such steps require additional reagents and can generate waste.

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Safer Solvents and AuxiliariesThe use of auxiliary substances (e.g., solvents or separation agents) should be made unnecessary whenever possible and innocuous when used. Design for Energy EfficiencyEnergy requirements of chemical processes should be recognised for their environmental and economic impacts and should be minimised. If possible, synthetic methods should be conducted at ambient temperature and pressure.

THE 12 PRINCIPLES OF GREEN CHEMISTRY Catalysis

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

Design for Degradation

Chemical products should be designed so that at the end of their function they breakdown into innocuous degradation products and do not persist in the environment.

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.

Inherently Safer Chemistry for Accident Prevention

Substances and the form of a substance used in a chemical process should be chosen to minimise the potential for chemical accidents, including releases, explosions, and fires.

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THE MAJOR USES OF GREEN CHEMISTRY

Energy Global Change Resource Depletion Food Supply Toxics in the Environment

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WATER AS A SOLVENT

Universal solvent Non-toxic Non-flammable Cheap Easily available Non-volatile Less hazardous as compared to other solvents

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IONIC LIQUIDS

Ionic liquids are salts that are liquid at low temperature- many at room temperature or below- and that in a molten form are composed wholly of ions.

Molten salts are salts with high boiling point. Most commonly use cations are N-alkyl-

pyrimidine, 1-alkyl-3-methyl imidazole, tetraalkyl-phosphonium, tetraalkyl-amonium.

Some possible anions are used like hexaflurophosphat, tetrafluroborate.

Most common alkyl chains are Ethyl, Butyl, Hexyl, Octyl.

SALIENT FEATURES OF THE ILS

o Very low vapour pressure - no toxic fumes .o Large operating range of temperature, -40 0C to

3500C.o Good thermal stability - non flammableo Dissolves in inorganic salts.

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PROPERTIES OF ILS

1. Stability,

2. High electrical conductivity,

3. Colour,

4. Higroscopicity,

5. Hydrophopicity.

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APPLICATIONS OF IONIC LIQUIDS

Chlorinated Phenols, ILs as separating agent.

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DISADVANTAGES

IL’s impact on aquatic ecosystems Toxic aspects

SUPERCRITICAL FLUID

A supercritical fluid is any substance at a temperature and pressure above its critical point.

Critical point is defined as the temperature and

pressure at which the liquid and gaseous phases of a pure stable substance become identical. It is also called Critical state.

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Phase diagram

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ADVANTAGES OF SUPERCRITICAL LIQUIDS Easy solvent removal and recycling. Increased reaction rate or increased solubility. Energy requirement is less.

Limitations of scCO2

Poor solubility of many substrates in scCO2.

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APPLICATIONS OF SUPERCRITICAL LIQUIDS

1. Supercritical fluid extraction.

2. Dry-cleaning.

3. Supercritical fluid chromatography.

4. Supercritical drying.

5. Supercritical water oxidation.

6. Biodiesel production.

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CATALYSIS FOR GREEN CHEMISTRY

Catalysis: It is the change in rate of a chemical reaction due to the participation of a substance called a catalyst.

Positive catalysts: Catalysts that speed the reaction.

Inhibitors (negative catalysts): Substances that interact with catalysts to slow the reaction.

Promoters: Substances that increase the activity of catalyst.

Catalytic poisons: Substance that deactivate catalyst.

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SIGNIFICANCE OF CATALYSIS Energy processing. Bulk chemicals. Fine chemicals. In the environment.

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TYPES OF CATALYSTS

Heterogeneous catalysts

Homogeneous catalysts

Electrocatalysts

Organocatalysts

SOLVENT FREE REACTIONS

A Dry media reaction or solid-state reaction or solventless reaction is a chemical reaction system in the absence of a solvent.

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ADVANTAGES

1. Economical

2. Environmentally friendly

3. Development of a recyclable catalyst.

MICROWAVE ACTIVATION

The utilization of a set of principles that

reduces or eliminates the use or generation

of hazardous substances in the design,

manufacture and application of chemical

products" Is nothing but the microwave

chemistry.

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MICROWAVE HEATING

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Microwave HeatingMicrowave standing waves cause heating throughout the sample

StandingWaves

Conventional HeatingRadiative heating of sample exteria followed by conductive heating through sample

RadiationRadiationConduction

The use of microwave energy reduces the heat-up and cool-down time for reactions and employs 50% less power than equivalent electric appliances.

MICROWAVE ASSISTED ORGANIC SYNTHESIS (MAOS)

MICROWAVE HEATING NORMALHEATING

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Microwave Heating Microwave heating works through three mechanisms: -

Dipolar polarisation (Oscillation of Polar molecules) :

Dipolar polarisation (Conduction Mechanism - Oscillations of Electrons or Ions):

Interfacial polarisation:

Can be considered as the combination of Conduction and Dipolar polarization. It is important for heating systems that comprise of a conductiong material dispersed in a non-conductiong material.

E.g., Dispersion of metal particles in Sulphur.

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Advantages

a) Rate enhancement

b) Higher chemical yield

c) Energy efficiency

d) Prevents pollution

e) Instant on / off

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Applications Applications in chemical synthesis

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Limitations 1) Lack of Scalability

2) Limited Applicability

3) Safety hazards relating to the use of microwave

heating apparatus

4)Health hazards

SONOCHEMISTRY

Introduction

Ultrasonic activation is one of the modern ways of chemical reactions accelerating. It applies ultrasound and not only increase rate of chemical reaction, but also increases percent of reacted substances.

Ultra sound utilizes interaction between high-frequency sound waves and matter to obtain information about the composition, structure and dimensions of materials through which it propagates.

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ULTRASOUND

transducers bonded to the base

waterreaction mixture

thermostated stainless

steel tank

Application of ultrasound to chemistry

Decrease of reaction time , Incrase the yield, Activation of metal and solid …

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ADVANTAGES

Ultrasound in food processing and industry. Extraction of lipid and protins. Ultrasonic cleaning. Microbial and enzyme inactivation.

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Committee, Hypertension. 22(3). P.392 (1993) 4. Burger’s Medicinal Chemistry, ed.6., vol.-2, Manfred Wolf, Wiley–

Interscience, New York., 268-270.5. Honkanen E., J.Heterocycl.Chem., 17, 797(1980).6. Althius T.S., J.Med.Chem., 20, 146(1977), U.S.Pat., 351836(1970).7. K.Gewald, Angew.Chem., 73,114(1961);Chem. Abstr., 55,2383(1961).

SELECTED REFERENCES

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