Green Chemistry & Its Principles

Presented By: Ayesha Ishfaq

Roll # 357

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Waste

Materials

Hazards

Risks

Energy

Cost

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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.

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To reduce adverse environmental impact, try appropriate and

innovative choice of material & their chemical transformation.

To develop processes based on renewable rather than non-

renewable raw materials.

To develop processes that are less prone to obnoxious chemical

release, fires & explosion.

To minimize by-products in chemical transformation by redesign of

reactions & reaction sequences.

To develop products that are less toxic.

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To develop products that degrade more rapidly in the environment

than the current products.

To reduce the requirements for hazardous persistent solvents &

extractants in chemical processes.

To improve energy efficiency by developing low temperature & low

pressure processes using new catalysts.

To develop efficient & reliable methods to monitor the processes

for better & improved controls.

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

formed”

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It is the measure of waste.

It is represented by E and it should be minimum.

E =𝑇𝑜𝑡al mass of effluent formed

𝑀𝑎𝑠s of desired products× 100

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“Synthetic methods should be designed to maximize

incorporation of all materials used in the process into the final

product”

Atom economy (atom efficiency) describes the conversion efficiency

of a chemical process in terms of all atoms involved (desired

products produced).

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Traditionally, the efficiency of a reaction has been measured by calculating thepercent yield.

Let us assume that the following substitution reaction gives 100% yield. Whilethis is admirable, we can shed more light on the efficiency of a reaction bycalculating the “percent atom economy” as follows:

𝐴𝑡𝑜𝑚 𝐸𝑐𝑜𝑛𝑜𝑚𝑦 =𝑀𝑜𝑙. 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝐷𝑒𝑠𝑖𝑟𝑒𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑡

𝑀𝑜𝑙. 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑎𝑙𝑙 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠× 100

= (137/275) X 100 = 50%

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Simply put, even if our percent yield is 100%, only half the mass of

the reactants atoms are incorporated in the desired product while the

other half is wasted in unwanted by-products.

Imagine telling your mom you baked a cake and threw away half the

ingredients!

Thus chemists must not only strive to achieve maximum percent

yield, but also design syntheses that maximize the incorporation of

the atoms of the reactants into the desired product.

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“Wherever practicable, synthetic methods should be designed to

use and generate substances that possess little or no toxicity to

people or the environment”

“wherever practicable.” Saying those two words implies that it may

not be practical or possible to avoid using substances that are

toxic, and that’s why most chemists use to try to avoid applying

this principle to their work.

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“Chemical products should be designed to effect their desired

function while minimising their toxicity”

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Achieving this goal requires an understanding of not only chemistry

but also of the principles of toxicology and environmental science.

Highly reactive chemicals are often used by chemists to manufacture

products because they are quite valuable at affecting molecular

transformations.

However, they are also more likely to react with unintended biological

targets, human and ecological, resulting in unwanted adverse effects.

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

agents, etc.) should be made unnecessary wherever

possible, and innocuous when used”

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Choose solvents that make sense chemically, reduce the energy

requirements, have the least toxicity, have the fewest life cycle

environmental impacts and don't have major safety impacts.

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“Energy 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”

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Developing the alternatives for energy generation (photovoltaic,

hydrogen, fuel cells, bio based fuels, etc.) as well as

Continue the path toward energy efficiency with catalysis and

product design at the forefront.

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“A raw material or feedstock should be renewable rather than

depleting whenever technically and economically practicable”

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In the past 10 years, significant advances have been made in the

development of fuels, chemicals and materials from renewable feed

stocks from “thin air” with minimal impact on human health and the

environment.

These for example, have included biodiesel from plant oils and

algae, bioethanol and butanol from sugars and lignocellulose,

plastics, foams and thermosets from lignin and plant oils, and even

electronic materials from chicken feathers.

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“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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One of the best ways of doing this is the use of enzymes.

Enzymes are so specific that they can often react with one site of the

molecule and leave the rest of the molecule alone and hence

protecting groups are often not required.

A great example of the use of enzymes to avoid protecting groups

and clean up processes is the industrial synthesis of semi-synthetic

antibiotics such as ampicillin and amoxicillin

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“Catalytic reagents (as selective as possible) are superior to

stoichiometric reagents”

A catalyst is defined as “a substance that changes the velocity of a

reaction without itself being changed in the process”. It lowers the

activation energy of the reaction but in so doing it is not consumed.

This means that, in principle at least, it can be used in small amounts

and be recycled indefinitely, that is it doesn’t generate any waste.

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The reduction of a ketone to the corresponding secondary alcohol using

sodium borohydride or molecular hydrogen as the reductant.

Reduction with the former has an atom economy of 81% while reduction

with the latter are 100% atom economic, that is everything ends up in the

product and, in principle, there is no waste.

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“Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in

the environment”

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Green chemistry principles 3, 4, 5, and 12 guide designers to reduce

the hazards of chemicals.

Principle 10, however, guides the design of products that degrade

after their commercial function in order to reduce risk or the

probability of harm occurring.

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“Analytical methodologies need to be further developed to allow for

real-time, in-process monitoring and control prior to the formation of

hazardous substances.”

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Most chemists are familiar with laboratory analysis from their

undergraduate training.

But analysis can also be performed in-line, on-line, or at-line in a

chemical plant, a sub-discipline known as process analytical

chemistry.

Such analysis can detect changes in process temperature or pH

prior to a reaction going out of control, poisoning of catalysts can be

determined, and other deleterious events can be detected before a

major incident occurs.

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“Analytical 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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Green Chemistry Principle # 12 is known as the “Safety Principle”.

It may be the most overlooked of the twelve principles, yet it is the

logical outcome of many of the other principles. In fact it is practically

impossible to achieve the goals of Principle 12 without the

implementation of at least one of the others.

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Energy

Global Change

Resource Depletion

Food Supply

Toxics in the Environment

Computer Chips

Medicine

Biodegradable Plastics

Paint

The major uses of GREEN CHEMISTRY

Green chemistry offers a different approach to conventional

chemistry and engineering through the thoughtful application of

principles that aid the design of sustainable chemical products and

processes by focusing individuals on the development of innovative

solutions, opportunities, and challenges.

Applying these principles collectively will result in products and

processes that protect and benefit the economy, people, and the

planet and help us make significant strides toward a more

sustainable future.

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http://www.slideshare.net/hecrod/green-

chemistry3985228?related=1

http://www.slideshare.net/Santachem/green-chemistry-15990119

http://www.acs.org/content/acs/en/greenchemistry/what-is-green-

chemistry/principles.html

http://www.acs.org/content/acs/en/greenchemistry/what-is-green-

chemistry/principles/12-principles-of-green-chemistry.html

http://www.epa.gov/sciencematters/june2011/principles.htm

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