A complete and comprehensive approach towards green chemistry & its applications. it plays significance role to sustain user friendly environment by reducing waste and enhance energy efficiency & atom economy. It leads less hazardous chemicals that are easy to discard.
2. Green chemistry
An area of chemistry and chemical engineering that focus on the design
of products and processing that eliminate or minimize the use of and generation
of hazardous substances.
The design of chemical processes and products to reduce or to eliminate the
use and generation of toxic, poisonous, hazardous and bio-accumulative
chemical substances, that are more environmental friendly and reduce negative
impacts to human health and to the environment.
A new scientific approach based on Environment Protection, plays vital role in
controlling global warming, acid rain and climate change, 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
3. Principles of
Green
Chemistry
Real-time Analysis for
Pollution Prevention
Design for
Degradation
Catalysis
Reduce Derivatives
Design for
energy
efficiency.
Use of
Renewable
Feedstocks
Waste
Prevention
Less hazardous
synthesis
Designing Safer
Chemicals
Safer Solvents
and Auxiliaries
Design for Energy
Efficiency
Atom
Economy.
4. 1. Waste prevention
It is better to prevent waste formation than to treat or clean it after its
formation.
ü beneficial to carry out a synthesis in such a way that the formation of
waste products is minimum or absent.
ü If wastes are discharged into the atmosphere, seas and to land, it would
cause not only pollution, but expenditure would also be needed for
cleaning up.
6. 2. Atom Economy
“Synthetic methods should be designed to
maximize the incorporation of all materials
used in the process into the final product.”
• A synthesis is Perfectly Efficient or Atom
Economical if it generates significant
amount of waste which is not visible in
percentage yield calculation.
• Percent yield:
% Yield= actual yield / theoretical yield ×
𝟏𝟎𝟎
•Atom Economy: % AE = 𝑭𝑾 𝒐𝒇 𝒂𝒕𝒐𝒎𝒔 𝒖
𝒕𝒊𝒍𝒊𝒔𝒆𝒅 /𝑭𝑾 𝒐𝒇 𝒂𝒍𝒍 𝒓𝒆𝒂𝒄𝒕𝒂𝒏𝒕𝒔 × 𝟏𝟎𝟎
7. Atom Economy
Addition and Rearrangement reactions are 100% atom economical
reactions as all the reactants are incorporated into products.
While Substitution and Elimination reactions are less atom economical.
Atom economical reaction
In Propene-propane reaction 64.8% reactants are incorporated into product as it
takes place in presence of Nickel.
1. H3C-CH=CH2 + H2 H3C-CH2-CH3
less atom economical the % atom economy is 36.5%
2. CH3(CH2)4CH2OH +SOCl2 SO2 + CH3(CH2)4CH2Cl
8. 3. Less hazardous synthesis
Wherever practicable,
synthetic methodologies
should be designed to use and
generate substances that
possess little or no toxicity to
human health and to
environment.
Example of an unsafe drug is
THALIDOMIDE for
lessening the effect of nausea
and vomiting during
pregnancy. The child suffers
from birth defects like
deformed-limbs.
9. 4. Designing
Safer
Chemicals
For example: in the manufacture of Polystyrene, CFC’s which
contribute to ozone depletion and global warming are replaced by CO2
Synthetic methodologies should be designed to generate substances
that generate substances that possess less harmful or toxic products.
This principle focuses on choosing reagents that pose the least risk
and generate only safe by-products.
"Chemical products should be designed to preserve efficacy of
function while reducing toxicity.”
10. 5. Safer
Solvents
and
Auxiliaries
“The use of auxiliary substances like solvents,
separating agents, etc. should be made unnecessary
wherever possible or otherwise make
them innocuous.”
The solvent selected for a particular reaction
shouldn't cause any environmental pollution or
hazard e.g. benzene, alcohol.
•One major problem with many solvents is their
volatility that may damage environment and
human health.
To avoid this many reactions are carried out in
safer green solvents like ionic liquids, supercritical
CO2 fluid etc. which maintain the solvency of the
material and are also non-volatile.
12. 6. Design for Energy Efficiency
“it is important to recognize energy requirements for their
environmental and economic impacts and should be
minimized. Synthetic methods should be conducted at
ambient temperature and pressure.”
In any chemical synthesis the energy requirement
should be kept low for example:
If the starting material is soluble in a particular solvent,
the reaction mixture must be heated till the reaction is
complete.
If the final product is impure, it must be purified by the
process of distillation or recrystallization .
All these steps involve the use of high amount of energy
which is uneconomical.
13. 7. Use of Renewable Feedstocks
“A raw material or feedstock should be renewable rather
than depleting wherever technically and economically
practicable.”
•Renewable feedstocks are the wastes of other processes
and are often made from agricultural products. depleting
Feedstocks that comprises petroleum, coal or natural gas
are depleted from fossil fuels or are mined.
• For example :- Substances like CO2 generated from
natural sources and methane gas are considered as
renewable starting materials.
15. 8. Reduce
Derivatives
“ Unnecessary derivatization such as blocking
groups, protection/deprotection, temporary
modification of physical or chemical processes
should be minimized or if possible, avoid.”
• This is necessarily important to overcome
such steps because they required additional
reagents and can generate waste.
• Overall yield and atom economy decrease.
• Instead, more selective and better
alternative synthetic sequences that
eliminate the need for functional group
protection should be adopted.
16. 9. Catalysis
“Catalytic reagents (as selective as possible) are superior to
stoichiometric reagents.”
Use of a catalyst facilitates transformation without the
catalyst being consumed in the reaction and without being
incorporated in the final product.
Advantages
1. Better yields H3C-CH=CH2 + H2 H3C-CH2-CH3
Propene Propane the hydrogenation of olefins is carried out
in presence of nickel.
2. The reaction becomes feasible in those cases where no
reaction is normally possible.
3. Better utilization of starting material and minimum
waste product formation.
17. 10. Design for Degradation
Chemical products should be designed so that at the end of
their function they do not persist in the environment and
break down into innocuous degradation products.”
For example
• Sulfonated detergents
• Long Alkylbenzene sulfonates – 1950’s & 60’s
• Foam in sewage plants, rivers and streams Persistence
was due to alkyl chain
• Introduction of alkene group into the chain increased
degradation
• Chlorofluorocarbons (CFCs)
• Do not break down, persist in atmosphere and contribute
to destruction of ozone layer
• Insecticides like DDT tend to bio-accumulate in many
plant and animal species and incorporate into the food
chain resulting in population decline of beneficial insects
and animals.
18. 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.”
Real time analysis for a chemist is the
process of “checking the progress of
chemical reactions as it happens.”
Knowing when your product is “done”
can save a lot of waste, time and
energy.
19. 12. Inherently Safer Chemistry for
Accident Prevention
“Substances and the form of a substance used in a chemical process should be
chosen to minimize potential for chemical accidents, including releases,
explosions, and fires.”
Design chemicals and their forms (solid, liquid, or gas) to minimize the potential
for chemical accidents including explosions, fires and releases to the
environment.
Example of such incident due to lack of such measures:-
December 3, 1984 – poison gas leaked from a Union Carbide factory, killing
thousands instantly and injuring many more (many of who died later of
exposure). Up to 20,000 people have died as a result of exposure (3-8,000
instantly). More than 120,000 still suffer from ailments caused by exposur
21. Merits of green synthesis
Green synthesis” of nanoparticles makes use
of environmentally friendly, non-toxic and
safe reagents.
• Nanoparticles synthesized using biological
techniques or green technology have diverse
natures, with greater stability and
appropriate dimensions since they are
synthesized using a one-step procedure.
22. Merits of green synthesis
An important concern about the synthesis of SNPs
is the formation of hazardous wastes, noxious by-
products and ruinous pollutants. The best
solution to mitigate and/or exclude these noxious
substances are plant mediated biosynthesis of SNPs.
Eco-benevolent SNPs from plant extracts have
been identified as precious nanomaterial in various
agricultural, biomedical and catalytic
applications including lithium-sulfur batteries,
pesticides, fungicides, carbon nanotube
modification, gas sensor and neutron capture in
cancer therapy because of their splendid
performance and selectivity
