Sustainable Chemistry
B.Tech F.Y SEM I
CHEMISTRY
Dr.Shabdashri
Dr.Shabdashri
Sustainable Chemistry
• Green Chemistry is 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 .
• Green Chemistry is a recent approach to design of energy efficient
processes and the best form of waste disposal.
• Green chemistry is the use of chemistry for pollution prevention
• The chemical reactions involved are always associated with certain
by-products which are harmful for the environment and cause
severe pollution problems.
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• All chemicals are toxic in nature hence to minimize the problems of
environmental pollutions and hazardous waste it necessary to
review and modify all the chemical processes used for
manufacture .
• Thus design of harmless processes to produce various products has
emerged as a new branch commonly known as "clean chemistry" or
"Green Chemistry" or "Environmentally benign chemist!".
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Importance of Sustainable Chemistry:
1. Prevents pollution at the molecular level.
2. Is a philosophy that applies to all areas of chemistry, not a single
discipline of chemistry.
3. Applies innovative scientific solutions to real-world environmental
problems.
4. Reduces the negative impacts of chemical products and processes
on human health and the environment.
5. Lessens and sometimes eliminates hazard from existing products
and processes.
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Benefits of Green Chemistry:
1. Human health:
2. Cleaner air: Less release of hazardous chemicals to air leading to
less damage to lungs
3. Cleaner water: less release of hazardous chemical wastes to
water leading to cleaner drinking and recreational water
4. Increased safety for workers in the chemical industry; less use of
toxic materials; less personal protective equipment required; less
potential for accidents (e.g., fires or explosions)
5. Safer consumer products of all types: new, safer products will
become available for purchase; some products (e.g., drugs) will be
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made with less waste
some products (e.g., drugs) will be made with less waste; some
products (i.e., pesticides, cleaning products) will be replacements
for less safe products
6) Safer food: elimination of persistent toxic chemicals that can enter
the food chain; safer pesticides that are toxic only to specific pests
and degrade rapidly after use
7) Less exposure to such toxic chemicals as endocrine disruptors
8) Environment: Many chemicals end up in the environment by
intentional release during use (e.g., pesticides), by unintended
releases (including emissions during manufacturing), or by disposal.
Green chemicals either degrade to innocuous products or are
recovered for further use (recyclable) Dr.Shabdashri
10) Plants and animals suffer also from toxic chemicals in the
environment
11) Lower potential for global warming, ozone depletion, and smog
formation
12) Less chemical disruption of ecosystems
13) Economy and business: Higher yields for chemical reactions by
consuming smaller amounts of feedstock at reduced reaction time
14) Fewer synthetic steps, often allowing faster manufacturing of
products, increasing plant capacity, and saving energy and water
15) Reduced waste, eliminating costly remediation, hazardous waste
disposal
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Goals /Objectives of Green Chemistry
• The objective of green chemistry is to minimize the environmental
pollution caused due to chemical processes. Hence it aims to
design harmless chemical processes with respect to
1. Chemicals used
2. Products formed
3. By products generated
4. waste generated from the process energy requirement
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• The green chemistry utilizes a set of principles that reduces or
eliminates the use or generation of hazardous substances in the
manufacture and facilitates the formation of product which is safe for
the use.
• The set of these principles is known as "12 principles of Green
Chemistry".
The principles cover such concepts as :
• The design of processes to maximize the amount of raw material
that ends up in the product
• The use of safe, environment-benign substances, including
solvents,whenever possible
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• The design of energy efficient processes
• The 12 principles of green chemistry were developed in the 1990s
by chemists who wanted to address the impact of their activities
in terms of safety and sustainability.
• These principles are still relevant today, with many laboratories and
manufacturing facilities adopting them to improve safety and reduce
the environmental impact of their chemical reactions. The best part
is that green chemistry practices can be implemented anywhere,
from small benchtop experiments to massive, industrial scales.
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Dr.Shabdashri
1: Waste Prevention
The first principle is to do with waste prevention; it’s better
to prevent waste than have to treat and/or dispose of it
after the reaction.
Just as in the hierarchy of hazard controls, we should
identify and remove inefficient reactions that generate an
excessive amount of waste.
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The Environmental Impact Factor (E-Factor) is used to
quantify the amount of waste generated per kilogram of
product; a reaction that produces 2 kg of waste alongside 1 kg
of product would have an E-Factor of 2.
More waste means less product, which also needs to be
treated and disposed of.
Apart from chemical waste prevention, time and effort can also
be reduced by assessing the processes in place.
In a laboratory, an inefficient reaction process might mean
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an extra waste or an extra hour of heating.
However, in an industrial setting, this can mean tankers of
excess waste and high power usage.
Chemical waste treatment and disposal is an expensive
process, further adding to costs.
Therefore waste prevention is an important consideration for
every reaction.
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2: Atom Economy
Atom economy (AE) is another useful tool that allows us to
calculate the efficiency of a reaction.
An atom-efficient reaction is, therefore, one that has a relatively
high AE value.
It is taken to be the total atomic weight of the product against
the total atomic weight of the substrates.
A reaction with a low AE will consume a lot more resources as
starting materials to yield less product, likely generating more
waste.
So, atom economy more wastage will be less. Hence, 2nd
principle supports 1st principle
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Atom Economy is the ratio of "the mass of the desired product"
by "the total mass of the reactants", and can be expressed in
percentage as illustrated in the formula below.
Assume for a reaction:
A + B → C + D, where ‘C’ is the desired product
The Atom Economy can be calculated as,
reactants
Atom Economy for substitution reaction is less,
For Addition reaction it is more i.e 100 %
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Rules:-
1) Balance the chemical reaction
2) Write down the molecular formula for each reactant and
product
3) By using atomic weight calculate molecular weight of reactants
and products.
4) Don’t consider the molecular weight of solvents, catalyst, or
other side products while calculating atom economy.
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Examples:- Fe =55.85, B=10.81, Br= 79.90, K=39,S=32,P=30.97
1) C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g)
Atomic masses: C = 12, H = 1 and O = 16
Molecular weight of C6H12O6(aq) = (6x12 + 12x1 + 6x16)= 180
formula mass of ethanol product = (2x12 + 5x1 + 1x16 + 1x1) = 46
relative mass of desired useful product in the equation = 2x 46 = 92
Atom economy = Molecular weight of desired product
X 100
Molecular weight of all reactant
100 x 92/180 = 51.1%
2)
3)
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4)
5)
6)
7)
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8)
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Sr. Atom Economy Percentage Yield
No
1. Atom economy is the determination of Percentage yield is the actual yield
the efficiency of a chemical synthesis obtained from a chemical synthesis
with respect to the atoms used during the reaction, with respect to the theoretical
synthesis reaction. yield.
2. Atom economy is calculated to estimate Percentage yield is calculated to
the efficiency of a process and to determine the amount of product given
determine the waste of atoms practically when compared to the
theoretical expectations
3. Atom economy is calculated by dividing Percentage yield is calculated by dividing
the molar mass of the desired product by the actual yield of the product from the
the molar mass of all the reactants theoretical yield of the product.
4 It is constant for fixed method It can be vary
5
reactants
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Dr.Shabdashri
Atom Economy is beneficial to promote the atom economy as it
helps in:
Minimizes the waste, and reduces the cost associated with
waste management and treatment.
Simplifies storage and transportation.
Minimizes potential pollution, prevents companies from legal
pursuits and reduces emissions, etc.
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3. Less Hazardous Chemical Synthesis
Wherever practicable, synthetic methods should be designed to
use or generate chemicals that pose little or no toxicity to the
environment and human health.
The Retrosynthesis principle can be applied in synthesis so that
less toxic starting material can be used in synthesis and a safer route
can be designed so that toxic by-products are not produced.
Reducing the number of steps in synthesis will also ensure less
by-product formation.
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Starting material selected should be least toxic.Eg: pyridine,
βnaphthyl amine are carcinogenic should be avoided.
Alternative pathway should be chosen if intermediates,
reagents or products are toxic.
This principle tells us to synthesize less toxic or harmless products
to humans and environment.
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Example:-
In 1984 MIC gas released in Bhopal cases death of lots of people.
MIC is intermediate in agricultural pesticide synthesis is posinous
substance. [also violated principles 4, 12].
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Reaction
synthesis
Not in MST but in
ESE
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4. Design of safer chemicals
Products should be designed to preserve the efficiency of desired
function while reducing toxicity
This modification should be reflected up to the molecular
level of the chemical’s design.
This principle will be beneficiary as it eliminates the
necessity of chemicals which are carcinogenic,
neurotoxins, asthmagens or hormone, etc. such disruptors
and is essentially safe to the Earth.
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For example, Antifoulants are used along with paints to prevent
the growth of barnaches, diatoms, and algae in the hulls of ships.
Traditionally used antifoulants such as tributyltin oxide (TBTO) is
extremely toxic and don’t degrade. 'Sea nineTM211 antifoulant‘ is
being used instead which is acutely fatal to only the nosy foulants
and not to other organisms and degrades easily.
Many insecticides like DDT, gamaxane, aldrin etc. which are toxic
to humans, instead of that use biological pesticides.
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5. Safer solvent and Auxiliaries
Most of the industries from polymer to pharmaceutical industries
and other chemical allied industries use solvents at some point in
their manufacturing.
In general, the use of solvents should like acetone, benzene, ether
which are (highly flammable) CCl4, CHCl3 (causes health risk), be
avoided, but that is not possible in all cases. So we can possibly
replace toxic, non-recyclable solvents with safer solvents.
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The auxiliary substances (Inorganic and organic solvents) should
be replaced by safer and ecofriendly green solvents like Ionic
liquids(IL), supercritical CO2 fluid and supercritical water.Promote
solvent free synthesis like: adsorbents like clays, zeolites, silica and
alumina.
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6. Design for Energy Efficiency
Energy efficiency is important for sustainability.
Energy-intensive reactions that require extremely high reactions
are unfavorable from a green chemistry standpoint; there are often
ways to reduce energy barriers.
Furthermore, fossil fuel depletion and climate change are forcing
us to invest in renewable energy technologies, and it is no different
from chemical reactions.
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Biofuels, solar, wind, hydro and geothermal sources of energy and
other sources of ‘clean’ energy currently account for roughly 20% of
the world’s electricity generation
Recently microwave radiations, ultrasound are also used which
requires very less energy
Energy efficiency can be increased by,
a) proper heat transfer,
b) minimal wastage of energy during the process.
Many chemicals are formed by fermentation process which req.
less energy. (milk to curd)
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7. Use of Renewable Feedstocks
The increasing awareness of sustainability in our modern society has
led to switch to the use of biomass as a feedstock and an energy
source.
Lignocellulosic biomass ( plants and plant-based materials not
used for food or feed) is abundant in nature, renewable, and
sustainable resource for producing biofuels, bioproducts, and
biopower.
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Synthesis of adipic acid from corn starch as starting material
instead of benzene which is carcinogenic
A shift to renewable feedstocks in chemical synthesis will be a
necessity in the future as we face fossil fuel depletion, with biomass
presenting a viable option.
Many renewable materials can be obtained from living organisms,
such as cellulose, starch, glycerol and vegetable oils.
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Soybean (soy ink) is used to replace traditional inks in printer
cartridges.
Green synthetic approach was adopted for adipic acid synthesis
from glucose (obtained from corn starch or cellulose). It replaces
benzene as reactant. Benzene is carcinogen.
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Reaction
synthesis
Not in MST but in
ESE
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8. Reduce Derivatives
In this principle, the reaction takes place at a particular functional
group blocking unnecessary waste generation by reducing the
process steps with the use of enzymes, catalysts, or solvent,
therefore, reducing demand for feedstock and utilities required for
down-streaming hence increasing overall economy and efficiency of
the process.
Derivatives increases no. of steps too
Additional reagents are req. Which will generate more waste
Eg: synthesis of Ibuprofen : traditional pathway involves more no.
of steps and less atom economy (40%), green synthesis is beneficial
with high atom economy.
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Green chemistry principal
followed no 2,8,9
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9. Catalysis
Catalytic Processes" are achieving the goals of Environmental
protection and economic benefit.
Catalysts provide many benefits from lower energy consumption to
increased selectivity of the reaction and allow a decreased use of
harmful and toxic chemical agents.
Zeolites, Clays are promising and benign catalysts used in
Heterogeneous Catalysis, which can replace the use of harmful
catalysts. Enzymes are Biocatalysts which are natural substances
derived from Biological sources, are renewable and Biodegradable.
BHC for ibuprofen synthesis, Ionic liquid as catalyst
The Haber-Bosch process—another Nobel Prize-winning reaction—
is a famous example of catalysis, with an iron-based catalyst
promoting the reaction of nitrogen and hydrogen to form ammonia,
at a remarkable efficiency of 97%. Dr.Shabdashri
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10. Design for Degradation
This principle stands for, “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”.
That means during the usage of chemicals it should be stable and
do not persist the environment but after usage, it should be
degraded into small molecules that are not harmful to the
environment and humans.
Eg: DDT is a pesticide whose residue remain in soil for years causing
pollution. Instead use biological insecticides.
Plastics or poly styrene which are popular packaging materials are
non-degradable hence solid waste. Alternatives are plastics from
cellulose and packing pellets made from starch
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11. Real-time analysis for Pollution prevention
Real-time analysis in Chemical and allied industries are essential
for production, transportation, and especially in the case of
pollution prevention. Pollution in the industrial premises could
become a potential threat to various probable hazards.
The real-time analysis opens the scope of online process control
and prevents any possible threats hence increasing overall profit to
the industry as well as ensure safety to the environment.
Monitoring and control prior to the formation of hazardous
substances.
Examples: Preparation of ethylene glycol: if the reaction is not
monitored properly, at higher temp. toxic compounds can be
generated
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12. Inherently safer chemistry for accident prevention
It involves choosing a safer chemical to mitigate the chances
of occurrence of an accident.
It benefits the industry as well as the environment as it acts as a
safeguard against calamitous industrial or laboratory accidents.
Avoidance of hazard is the key.
The infamous Bhopal Gas Tragedy could have been avoided by the
usage of methylamine instead of methyl isocyanate (MIC). 1-
naphthol reacts with phosgene to give 1-napthylcholoroformate
which can react with methylamine to produce carbaryl( the target
product of the Union Carbide plant in Bhopal).
Minimizing temperature, pressure use of catalyst can avoid
accidents.
Dr.Shabdashri
The infamous Bhopal Gas Tragedy could have been avoided by the
usage of methylamine in lieu of methyl isocyanate (MIC). 1-
naphthol reacts with phosgene to give 1-napthylcholoroformate
which can react with methylamine to produce carbaryl( the target
product of the Union Carbide plant in Bhopal).
Minimizing temperatur, pressure use of catalyst can avoid
accidants.
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Significance of Green chemistry :-
Environmental laws, the prospect of competitive advantages are
pushing chemical industry to develop cleaner chemical process.
1) The design of environmentally compatible chemical reactions
help to approach pollution concern and sustainability at source.
2) For eco-friendly green organic synthesis must meet following
concerns:
a) Avoid waste
b) Be atom efficient
c) Avoid use and production of toxic and dangerous chemicals and
synthesis of biodegradable products
d) Avoid auxiliaries (solvents)
e) Reduce energy req.
f) Use renewable materials
g) Catalyst for stoichiometric reagents
3) This area of chemistry aims to replace toxic chemicals to greener
ones.
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