chapter 2 green chemistry. green chemistry definition green chemistry is the utilisation of a set of...

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Chapter 2

Green Chemistry

Chapter 2

Green Chemistry



GREEN CHEMISTRY

DEFINITION

Green Chemistry is the utilisation 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 .



GREEN CHEMISTRY IS ABOUT

• Waste Minimisation at Source

• Use of Catalysts in place of Reagents

• Using Non-Toxic Reagents

• Use of Renewable Resources

• Improved Atom Efficiency

• Use of Solvent Free or Recyclable Environmentally

Benign Solvent systems



Green Chemistry Is About...

Cost

Waste

Materials

Hazard

Risk

Energy



Chemistry is undeniably a very prominent part of our daily

lives.

Chemical developments also bring new environmental

problems and harmful unexpected side effects, which

result in the need for ‘greener’ chemical products.

Why do we need Green Chemistry ?

A famous example is the pesticide

DDT.



Green chemistry looks at pollution prevention on the molecular

scale and 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.



Transportation - production of gasoline and diesel from

petroleum, fuel additives for greater efficiency and reduced

emissions, catalytic converters, plastics to reduce vehicle

weight and improve energy efficiency.

Clothing - man-made fibres such as rayon and nylon, dyes,

water proofing and other surface finishing chemicals.

Sport - advanced composite materials for tennis and squash

rackets, all-weather surfaces.



Safety - lightweight polycarbonate cycle helmets, fire-retardant

furniture.

Food - refrigerants, packaging, containers and wraps, food processing

aids, preservatives.

Medical - artificial joints, ‘blood bags’, anaesthetics, disinfectants, anti-

cancer drugs, vaccines, dental fillings, contact lenses, contraceptives.

Office - photocopying toner, inks, printed circuit boards, liquidcrystal

displays.

Home - material and dyes for carpets, plastics for TVs and

mobilephones, CDs, video and audio tapes, paints, detergents.

Farming - fertilizers, pesticides.



Atom economy is a measure of how many atoms of reactants

end up in the final product and how many end up in

byproducts or waste. The real benefit of atom economy is

that it can be calculated at the reaction planning stage from

a balanced reaction equation. Taking the following

theoretical reaction:

X + Y = P + U

the reaction between X and Y to give product P may proceed

in 100% yield with 100% selectivity but because the

reaction also produces unwanted materials U its atom

economy will be less than 100%.

ATOM ECONOMY



ATOM ECONOMIC REACTIONS

Rearrangement Reactions

Rearrangements, especially those only involving heat or a

small amount of catalyst to activate the reaction, display

total atom economy. A classic example of this is the Claisen

rearrangement, which involves the rearrangement of

aromatic ally1 ethers.



Substitutions are very common synthetic reactions; by

their very nature they produce at least two products, one of

which is commonly not wanted. As a simple example 2-

chloro-2-methylpropane can be prepared in high yield by

simply mixing 2-methylpropan-2-o1 with concentrated

hydrochloric acid (Scheme 1.10). Here the hydroxyl group

on the alcohol is substituted by a chloride group in a facile

SNl reaction. Whilst the byproduct in this particular

reaction is only water it does reduce the atom economy to

83%.

ATOM UN-ECONOMIC REACTIONS

Substitution Reactions



Elimination reactions involve loss of two substituents from

adjacent atoms; as a result unsaturation is introduced. In

many instances additional reagents are required to cause the

elimination to occur, reducing the overall atom economy

still further. A simple example of this is the E2 elimination

of HBr from 2-bromopropane using potassium t-butoxide

(Scheme 1.12). In this case unwanted potassium bromide

and t-butanol are also produced reducing the atom economy

to a low 17%.

Elimination Reactions



Wittig reactions are versatile and useful for preparing

alkenes, under mild conditions, where the position of the

double bond is known unambiguously. The reaction

involves the facile formation of a phosphonium salt from

an alkyl halide and a phosphine. In the presence of base

this loses HX to form an ylide (Scheme 1.15). This highly

polar ylide reacts with a carbonyl compound to give an

alkene and a stoichiometric amount of a phosphine oxide,

usually triphenylphosphine oxide.

Wittig Reactions



REDUCING TOXICITY

One of the underpinning principles of green chemistry is to

design chemical products and processes that use and

produce less-hazardous materials. Here hazardous covers

several aspects including toxicity, flammability, explosion

potential and environmental persistence.

A hazard can be defined as a situation which may lead to

harm, whilst risk is the probability that harm will occur.

From the point of view of harm being caused by exposure

to a chemical,



Many methods have now been developed for measuring the

potential harmful effects chemicals can have. Common tests

include those for irritancy, mutagenic effects, reproductive

effects and acute toxicity.

Measuring Toxicity



“It is better to prevent waste than to treat or clean up waste after it is formed”

Chemical

Process



“The use of auxiliary substances (e.g. solvents, separation

agents, etc.) should be made unnecessary wherever possible,

and innocuous when used”



HeatingCoolingStirringDistillationCompressionPumping Separation

Energy Requirement(electricity)

Burn fossil fuel

CO2 toatmosphere

GLOBAL WARMING



“A raw material of feedstock should be renewable rather than depleting wherever technically and economically practical”

Non-renewable Renewable



Poly lactic acid (PLA) for plastics production



Polyhydroxyalkanoates (PHA’s)



Energy

Global Change

Resource Depletion

Food Supply

Toxics in the Environment

The major uses of GREEN CHEMISTRY



Energy

The vast majority of the energy generated in the world today

is from non-renewable sources that damage the

environment.

Carbon dioxide

Depletion of Ozone layer

Effects of mining, drilling, etc

Toxics



Energy

Green Chemistry will be essential in

developing the alternatives for energy generation

(photovoltaics, hydrogen, fuel cells, biobased fuels,

etc.) as well as

continue the path toward energy efficiency with

catalysis and product design at the forefront.



Global Change

Concerns for climate change, oceanic temperature,

stratospheric chemistry and global distillation can be

addressed through the development and

implementation of green chemistry technologies.



Resource Depletion

Due to the over utilization of non-renewable resources, natural resources are being depleted at an unsustainable rate.

Fossil fuels are a central issue.



Resource Depletion

Renewable resources can be made increasingly viable

technologically and economically through green chemistry.

Biomass

Nanoscience & technology

Solar

Carbon dioxide

Chitin

Waste utilization



Food Supply

While current food levels are sufficient, distribution is

inadequate

Agricultural methods are unsustainable

Future food production intensity is needed.

Green chemistry can address many food supply issues



Food Supply

Green chemistry is developing:

Pesticides which only affect target organisms and

degrade to innocuous by-products.

Fertilizers and fertilizer adjuvants that are designed to

minimize usage while maximizing effectiveness.

Methods of using agricultural wastes for beneficial

and profitable uses.



Toxics in the Environment

Substances that are toxic to humans, the biosphere and all

that sustains it, are currently still being released at a

cost of life, health and sustainability.

One of green chemistry’s greatest strengths is the ability

to design for reduced hazard.



Prevention & Reduction

Recycling & Reuse

Treatment

Disposal

Pollution Prevention Hierarchy



The 12 Principles of Green Chemistry

1. Prevention

It is better to prevent waste than to treat or clean up waste after it

has been created.

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

Wherever practicable, synthetic methods should be designed to use

and generate substances that possess little or no toxicity to

people or the environment.



4. Designing Safer Chemicals

Chemical products should be designed to effect their desired function while

minimizing their toxicity.

5. Safer Solvents and Auxiliaries

The use of auxiliary substances (e.g., solvents or separation agents) should be

made unnecessary whenever possible and innocuous when used.

6. Design for Energy Efficiency

Energy requirements of chemical processes should be recognised for their

environmental and economic impacts and should be minimized. If possible,

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 practicable.

8. Reduce Derivatives

Unnecessary derivatization (use of blocking groups, protectiodde-protection, and

temporary modification of physicalkhemical processes) should be minimized

or avoided if possible, because such steps require additional reagents and can

generate waste.

9. Catalysis

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



10. Design for Degradation

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

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

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

chapter 2 green chemistry. green chemistry definition green chemistry is the utilisation of a set of...

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important area of chemistry

total atom economy

real benefit of atom

reaction planning stage

balanced reaction equation