A presentation on green chemistry by Harsh Shukla, M.Pharm., 2nd year

1. GREEN CHEMISTRY &
MICROWAVE ASSISTED
REACTIONS
SUBMITTED TO: SUBMITTED BY:
PROFESSOR DR. SHOBHIT SRIVASTAVA HARSH SHUKLA
M.PHARM 1st YEAR 2nd SEM
(PHARMACEUTICAL CHEMISTRY)
ROLL NO: 2203030576002
Dr. M.C. Saxena college of pharmacy

2. GREEN CHEMISTRY
 Green chemistry is the process of designing of various chemical products and
processes that reduce the generation of any of the hazardous substances.
 The practice of chemistry in a manner that maximizes its benefits while
eliminating or at least greatly reducing its adverse impacts on environment has
come to be known as green chemistry.
 It deals to develop a way of carrying out the chemical activities leading to the
safer products. Sometimes also corrected with the term Sustainable chemistry.

3. How green chemistry works:
• Waste minimization
• Use of catalyst in place of reagents.
• Using non toxic reagents.
• Use of renewable resources.
• Use of solvent free or recyclable environmentally benign
solvent systems.

4. PRINCIPLES OF GREEN CHEMISTRY
In 1998 Paul T. Anastas and Warner formulated the twelve principles of green
chemistry which serve as guidelines for the chemists to seek to lower hazardous
processes.

5. 1. Waste prevention
As the text simply states that chemical process used for manufacturing should be
optimized to produce minimum amount of waste possible.
A metric known as E-factor was developed to measure the amount of waste a process
created.
product
desired
the
of
Weight
product
by
or
waste
of
Weight
Factor
E 

SOLUTIONS:
Solvent less chemistry like use of microwave assisted reactions.
Process design.
Reaction choice
Recycling

6.  It is a measure of amount of atoms from the starting material that are present in the useful
products at the end of the process. Atom economy is a better measure of efficiency than the
yield of the reaction as the yield compares the amount of useful products obtained compared
to amount calculated theoretically.
The process that maximize the atom economy are preferred.
2. Atom economy
100
x
yield
l
Theoretica
yield
Actual
yield
Percentage 
100
x
product
by
product
desired
of
weight
Molecular
product
desired
of
weight
Molecular
economy
Atom
%


 More is the atom economy more is the reaction suitable for the green chemistry.

7. 3. Less hazardous chemical synthesis
Ideally we want chemicals we create for a purpose should not cause a health hazard
to humans. We also aim to make synthesis of chemicals as safe as possible, so the
aim is to avoid using hazardous substances or chemicals as a starting point if safer
alternatives are available.
 Whenever predictable synthetic methodologies should be used to generate
substances that possess little or no toxicity to human health and the environment.
Examples: Preparation of Adipic acid (Nylon 6,6) was done using
benzene but now glucose in presence of enzymes is used to generate
the Adipic acid.

8.  Chemical products should be designed to effect their desired function while
minimizing their toxicity. The design of safer chemical targets requires a
knowledge of how chemicals act in our bodies and in the environment. In some
cases, a degree of toxicity to animals or humans may be unavoidable, but
alternatives should be sought.
4. Designing the safer chemicals

9.  The use of auxiliaries substances (E.g: solvents, separating agents) should be made
unnecessary wherever possible and innocuous when used.
 They can also have a number of hazards associated with them, such as flammability
and volatility. Solvents might be unavoidable in most processes, but they should be
chosen to reduce the energy needed for the reaction, should have minimal toxicity,
and should be recycled if possible..
 E.g.: Water, supercritical carbon dioxide, Hydrogen peroxide, Polyethylene glycol.
5. Safer solvents and auxiliaries:

10.  Energy requirements of a chemical process should be recognized for their enviornmental
and economic impacts and should be minimized. If possible synthetic methods should be
conducted at the ambient temperature and pressure.
 Developing the alternatives for energy generation as well as continue the path toward the
energy efficiency with catalysis and products designed the forefront.
6.Design of energy efficiency:

11.  A renewable feedstock should be used . It should be renewable rather than
depleting whenever technically and economically practicable.
 Examples of the renewable feed stocks include:
Biodiesel (as an alternative fuel)
Bioplastics such as PLA manufactured from the corn and potato waste.
Use of agricultural and biological products.
7. Use of renewable feedstock

12. 8. Reduce derivatives
 Unnecessary derivatization should be avoided whenever possible, because such
steps require additional reagents and can generate waste.
 Unnecessary generation of derivatives such as the use of protecting groups should
be minimized or avoided if possible such steps require additional reagents and may
generate additional waste.

13. 9.Catalysis
 The use of catalyst can enable reactions with higher atom efficiency or economy.
These catalyst can be recycled many times over and don’t contribute to the waste.
 They also allow the reaction processes that are not favorable under normal
conditions.

14. 10. Design for degradation
 Organic pollutants do not decompose and can accumulate in the environment for
example halogenated compounds (DDT). Where possible, these chemicals should
be replaced with chemicals that are more easily decomposed by water, UV light, or
micro-organisms.
 Chemical products should be designed so that at the end of their function they
decompose into harmless degradation products and don’t have adverse impacts on
the environment.
 Compounds should be designed so that at end they can be easily degraded by the
microorganisms.

15. 11.Real time pollution prevention
 Monitoring a chemical reaction as it is occurring can help prevent release of
hazardous and polluting substances due to accidents or unexpected
reactions. With real time monitoring, warning signs can be spotted, and the
reaction can be stopped or managed before such an event occurs

16. 12.Safer chemistry for accident prevention
 Working with chemicals always carries a degree of risk. However, if hazards
are managed well, the risk can be minimized. This principle clearly links with a
number of the other principles that discuss hazardous products or reagents.
Where possible, exposure to hazards should be eliminated from processes, and
should be designed to minimize the risks where elimination is not possible.

17. EXAMPLES:
 Carbon dioxide as blowing agent:
 Polystyrene foam is a common material used in packing and food transportation.
Traditionally, CFC and other ozone-depleting chemicals were used in the production
process of the foam sheets, presenting a serious environmental hazard. Flammable,
explosive, and, in some cases toxic hydrocarbons have also been used as CFC
replacements, but they present their own problems.
 Dow Chemical discovered that supercritical carbon dioxide works equally as well as a
blowing agent, without the need for hazardous substances, allowing the polystyrene to
be more easily recycled. The CO2 used in the process is reused from other industries,
so the net carbon released from the process is zero.

18.  Hydrazine:
 Addressing principle 2 the peroxide process for producing hydrazine without cogenerating
salt. Hydrazine is traditionally produced by the olin rashig’s process from sodium
hypochlorite (the active ingredient in many bleaches) and ammonia.
 The net reaction produces one equivalent of sodium chloride for every equivalent of the
targeted product hydrazine:
NaOCl + 2 NH3 → H2N-NH2 + NaCl + H2O
 In the greener peroxide process hydrogen peroxide is employed as the oxidant and the side
product is water. The net conversion follows:
2 NH3 + H2O2 → H2N-NH2 + 2 H2O
 Addressing principle 4, this process does not require auxiliary extracting solvents. Methyl
ethyl ketone is used as a carrier for the hydrazine, the intermediate ketazine phase separates
from the reaction mixture, facilitating workup without the need of an extracting solvent.

19. 1,3-Propanediol:
Addressing principle 7 A green route to synthesise 1,3-propanediol, which is
traditionally generated from petrochemical precursors. It can be produced from
renewable precursors via the bio separation of 1,3-propanediol using a genetically
modified strain of E. coli.This diol is used to make new polyesters for the manufacture
of carpets.

20. Microwave Assisted Reactions
 Microwave assisted reactions are defined as the reactions that involve the
synthesis of materials using microwave energy or the microwave radiations.
 The microwave assisted reactions open up the new opportunities for a
chemist to setup the reactions that are not possible under conventional
heating as well as it is a less hazardous tool for organic synthesis.
 The microwave energy is used for the reactions as it is a non ionizing form of
energy that does not alter the molecular structure and only causes thermal
activation of the molecule.
 Molecules having high polar nature undergoes microwave heating whereas
the molecules having non polar nature, crystalline arrangement are less
susceptible to heating by these radiations.

21. What are microwaves…..?
 A microwave is a form of electromagnetic energy that falls at lower
frequency at the end of the electromagnetic spectrum.
 It is present between the infrared and radio wave region.
 Microwave uses the EMR that passes through material and cause
oscillation of molecules which produce heat.

22. Benefits of microwave assisted reactions
Better yield and higher purity.
Less energy requirement.
Uniform and selective heating.
Green synthesis.
Reproducibility.
Faster reaction

23. Heating Mechanism For Microwave Assisted Reactions
In microwave assisted reactions heating occurs by mechanisms which are:
a) Dipolar polarization
b) Conduction mechanism
a) Dipolar polarization mechanisms: Interaction of the electric field
component with the matrix is called dipolar mechanism.For a molecule to be
irradiated by a microwave the presence of dipole in a molecule is necessary.
Molecule irradiated with a microwave it aligns itself with the applied field
Rapidly changing electric field affects the orientation of dipoles which attempts to
align itself within the electric field of microwaves
Energy is generated due to collision between these molecules

24. CONDUCTION MECHNAISM
 If there are free ions or ionic species present in the substance being
heated. The electric field generates ionic motion as the molecules try to
orient themselves to the fats changing fields.
 During this the dissolved charged particles oscillate back and forth under
the influence of microwave which is ultimately responsible which causes
collision of charged particles with neighboring atoms or molecules which
created heat energy.

25. Conventional Heating Vs Microwave Heating
Conventional Heating
 Low reaction rates.
 Compound in the mixture are
heated equally
 More solvent is required
 Efficient external heating
 Heat flow: outside to inside.
Microwave Heating
 Increase in reaction rate.
 Specific material is heated.
 Less solvent
 Efficient internal heating
 Heat flow: inside to outside
 Specific temperature

26. Microwave Assisted Reactions In Green Chemistry
Microwave
assisted
drug
synthesis
Cycloaddition
Diels-Alder reaction
Heck reaction
Suzuki reaction
Mitsunobu Reactions
Epoxidation
Esterification
Coupling reactions
Glycosylation Reactions
Buchwald-HartwigReactions
Protection and
deprotection

27. HECK REACTION
Heck reaction involves the formation of C-C by using Pd(OAc)2, P(o-tolyl)3 as a
catalyst under microwave irradiation.It is a reaction of an unsaturated halide with
an alkene in presence of a base and a palladium catalyst to form a substituted
alkene.

28. Coupling reactions:
The coupling of thiophenols with aryl halides is carried out under microwave irradiation
using magnetite-Glu-Cu, providing diphenylsulphide having yield of 85–98%.

29. Esterification
Benzoic acid undergoes esterification with alcohol in presence of sulfuric acid under
microwave irradiation.

30. Mannich reactions
Mannich reaction is performed by the microwave-induced synthesis of β-amino ketones
(yield of 97%) via the three-component condensation of a substituted methyl ketone, an
aldehyde and an amine

31. Applications
a) Formation of β-lactam:
The formation of β-lactam involves the reaction between 2(benzyloxy)acetyl chloride and
N-benzylidenemethanamine in the presence of N-methyl morpholine and chlorobenzene
under microwave irradiation

32. b) Synthesis of Aspirin
The synthesis of aspirin is carried out by reacting salicylic acid with acetic anhydride under
microwave irradiation at 600W for three minutes, providing a yield of 85% whereas in
conventinal process it is around 72%.

33. c) Synthesis of Barbituric Acid
Barbituric acid is produced by the reaction between a malonic ester, urea and acetic anhydride
under microwave irradiation at 60°C for seven minutes.

34. ADVANTAGES
 Uniform heating occurs throughout
the material
 Process speed is increased
 Low operating cost
 Less by-product formation
 Reduction in heat loss from the
reaction vessel
 Less solvent used and more solvent-
free reactions achieved
DISADVANTAGES
 Heat force control is difficult
 The closed container is
dangerous because it may
explode.
 In situ monitoring.
 Water evaporation
 Expensive setup
 More maintenance cost

35. REFERENCES:
• Microwave-Assisted Green Chemistry Approach A Potential Tool for Drug
Synthesis in Medicinal Chemistry Biswa Mohan Sahoo, Bimal K. Banik,and
Jnyanaranjan Panda.
• https://www.sciencedoze.com/2021/01/microwave-assisted-reactions-in-
green.html#:~:text=Microwave%2Dassisted%20reactions%20in%20organic%2
0solvents&text=This%20reaction%20involves%201%2C4,reflux%20period%20
of%2090%20min.
• https://www.researchgate.net/publication/261872979_Microwave_assisted_
synthesis_a_green_chemistry_approach