An approach to green chemistry via microwave radiation. applications of microwave synthesis, microwave assisted organic reactions.

1. Microwave synthesis and
their applications
Presented by: Sheama Farheen Savanur

2. A green chemistry approach
 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.
 Out of the 12 principles of green chemistry, the following are
taken care through MW synthesis
 Prevention of waste
 Less hazardous chemical synthesis
 Design for energy efficiency
 Inherently safer chemistry for accident prevention

3. Introduction
Microwave chemical synthesis has become a method of choice for
chemists throughout so many industries. The technology allows
synthesis to be done faster and cleaner with reduced solvent
consumption as a “greener” process.
Microwave chemistry is the science of applying microwave
radiation to chemical reactions. Preparation of a desired
compound from available starting materials via some (multi-step)
procedure, involving microwave irradiation
The microwave region of the electromagnetic spectrum lies
between IR and radio-frequency corresponding to wavelength 1
cm to 1 m (frequencies 30 GHz to 300GHz)

5. Principle ( Fundamental Theory)5
Microwave radiation
Dipolar polarization Ionic conduction
Electric component

6. Dipolar Polarization6
• Loss Tangent (Energy Dissipation Factor) –
a measure of the ability to absorb microwave energy and
convert it into thermal energy (heat)
• Derived from Maxwell’s equation
tanδ = ε”/ε’
• δ = dissipiation factor
• ε” = loss factor
• ε’ = dielectric constant
• Reaction medium with high tanδ value
efficient absorption
rapid heating

7. According to Arrhenius equation:
7
-Ea/RT
Rule of Thumb: for every 10°C increase in temperature the
rate of reaction becomes twice
80 °C 90 °C 100 °C 110 °C 120 °C 130 °C 140 °C 150 °C 160 °C
8 hr 4 h 2 hr 1 hr 30 min 15 min 8 min 4 min 2 min
Increasing temperature
Decreasing reaction time
Ionic conduction
• Due to translational motion of electric charges when an electric field is
applied
• Ions cause increased collision rate and convert kinetic energy to heat.
k =A*e

8. Microwave heating and Conventional
heating
Microwave heating can be divided into two kinds:
Thermal effects Non-thermal effects
Caused by different
temperature regime
which can be created
due to microwave
dielectric heating
Caused by effects specifically
inherent to the microwaves
and are not caused by
different temperature regime

9. In case of conventional heating the heat gradient is from the
heating device to the medium and the heat transfer depends
on thermal conductivity, on the temperature difference across
the material and on convection currents, therefore
temperature increase is often rather slow.
While in case of microwave heating the heat is dissipated
inside the irradiated medium(mass heating) and heat transfers
from the medium to outside. Due to mass heating effect much
faster temperature increase can be obtained depending
upon microwave power and loss factor of material being
irradiated.

10. Microwave assisted organic reaction
 Organic synthesis is an area which can benefit significantly from MW
irradiation. Microwave assisted organic reaction is a fast developing area in
synthetic organic chemistry. The basis being the observation that some
organic reactions proceed much faster and with nhigher yields under
microwave irradiation as compared with conventionl heating.
 To demonstrate the versatility of more chemistry, a variety of organic
reactions are discussed.
1. Catalytic Transfer Hydrogenation.
2. Preparation Of Oximes.
3. Condensation.
4. Nitrations.

11. 1. Catalytic Transfer Hydrogenation.
Hydrogenation of benzaldehyde has been carried out using
RuHCl(CO)PPh3)3.
It has been found that with constant microwave irradiation
the reaction was completed in 7 minutes as compared with
4 hours under standard reflux.

12. 2. Preparation Of Oximes.
Puciova and Toma have shown that in the preparation of
ferrocenyl oxime, in contrast to conventional heated
reactions, the microwave assisted reactions gave only the
thermodynamically stable isomer.

13. 3. Condensation.
Quinoxalines are effectively synthesized in a few minutes
by condensation reaction of o-phenylen diamine with
α-dicarbonyl compounds in ethanol under MWI

14. 4. Nitrations.
Nitrations of selected heterocyclic compound is carried out
by using Cu(NO3)2, Pb(NO3)2, KNO3 and NaNO3 in glacial
acetic acid under MWI.
The comparative study shows that Cu(NO3)2 in
glacial acetic acid is superior reagent than others. The
products were obtained in fairly good yields enhanced
rate of reaction using microwave irradiation.

15. Applications Of Microwave Heating
 In Material Chemistry- SiC is a large volume ceramic used in industries for
grinding wheels & in manufacturing of abrasion tools.
 In Catalyst Preparations- Synthesis of a high permeance NaA zeolite from
aluminate & silicate soln, Synthesis & study of vanadium dioxide & synthesis
of 1D manganese dioxide catalyst(OMS-1).
 In Nanotechnology- MW heating is used for the fabrication of nanoscale
objects, so as to give definite structures in much shorter time.
 In Polymer Synthesis- Faster heating rates with high quality/better yields
can be attained in polymer synthesis by MW heating. Polyacrylamide(PAM)
is used as a flocculating agent in waste water treatment was studied by
MW heating.
 In Waste Management- Handling of domestic & hazardous industrial waste
& nuclear waste can be done by MW heating. MW technology can be
applied for control of CFC, Methane, Greenhouse gases via microwave
catalysis reactions.

16. THANK YOU