c green Chemistry - used as microwave

1. Microwave Induced
Green Synthesis

2. • are used for heating purposes
• microwave reactions involve selective absorption
of electromagnetic waves by polar molecules,
non-polar molecules being inert to microwaves
• as a more efficient source of heating than
conventional steam (or oil heated vessels), since
the energy is directly imparted to the reaction
medium rather than through the walls of a
reaction vessel

3. Microwave-Assisted Organic Reactions
Microwave assisted organic reactions are useful in
the synthesis of active pharmaceutical ingredients
(APIs), drug intermediate and other compounds with
chemical and medicinal importance (analytical,
diagnostic, research). This technology improves the
chemical process and reduces the pollution (solvent
free methods). Microwave-assisted reactions
maximisestheefficientuseofsaferraw materials and
reduces the waste (toxic material) generation.

4. Speed
• Microwave reactions can be
completed in minutes. Some
chemical reactions complete in
seconds. In many cases, it reduces
the reaction time from hours to
minutes to seconds

5. Economy
• Microwave reactions utilize no or low volume
of solvents
• Microwave reactions reduce the cost per
microwave reactions mainly through
increasing the reaction rate there by yields
Cost effective

6. Simplicity
• The products of microwave reactions can be
isolated very easily and requires no
purification (recrystallization) in most cases
• Microwave reactions are reproducible
Consistency

7. Rapid optimization
• Microwave reactions complete very fast.
Hence, the organic reaction optimization can
be achieved faster than the conventional
synthesis
• Microwave reactions offer enhanced reaction
conditions.
Energy efficient reaction

8. Higher yield
• The rapid-efficient reaction inhibits the
byproducts formation and hence offers higher
yields of the products.
• The rapid-efficient reaction inhibits the
byproducts formation and hence offers highly
pure compounds
High purity

9. Superheating
• It takes the reaction environment to very high
temperature (super heating). It is very essential
for the several reactions such as substitution and
coupling reactions.
• The microwave heating can be utilized for all kinds of
organic reactions. It includes substitution, coupling,
rearrangement, oxidation and reduction, etc
Versatility

10. Theory of microwave heating
• The rotational states of the molecules
undergo excitation with electromagnetic
radiation
• The microwave irradiation, when absorbed by
organic molecules induces the rotational
changes
• The frequency of molecular rotation is similar
to the frequency of microwave radiation

11. • The molecule continually attempts to realign
itself with the applied electric field and
absorbs the energy. This effect is utilized in
microwave ovens to heat food materials

12. Microwave oven contains microwave generator
called as magnetron (inside the string metal box). It
receives electricity and converts them into high-
energy radio waves.
Microwave guide (channel) introduces microwave
heat energy (radiation) into the heat compartment.
The microwaves bounce back and forth off the
reflective metal walls of the heat compartment.
The microwaves penetrate the material to be
heated (reaction vessel) and vibrate them to cause
molecular friction. The rate of vibration decides the
heating and initiates the reaction.

13. Principles
• Microwave ovens more efficiently channel
heat energy into the molecules. In the
microwave heating process energy transfer
occurs by three mechanisms namely dipole
rotation, ionic conduction and interfacial
polarization

14. • Microwave ovens inject the energy directly
into the molecules, rather than warming the
outside walls of a reaction vessel to spread
heat by convection and conduction. High
frequency electromagnetic radiations (electric
fields) exert a force on charged particles of
molecules and that causes molecular friction
to generate super heat.

15. Ionic conduction
• Ionic conduction is the electrophoretic
migration of ions, when an electromagnetic
field is applied. The oscillating
electromagnetic field generates an oscillation
of electrons in a conduction and results
electric current
• The conduction mechanism generates heat
through resistance friction to the electric
current

16. Dipole rotation
• Rearrangement of dipoles with the applied
field
• Polar molecules are the ideal material for
dipolar polarization. Dipole polarization
depends on the dipole moment of a molecule
• The difference in the electro negativity of the
atoms and molecular symmetry is responsible
for this effect

17. • The alignment of polar molecules with an
oscillating electromagnetic field results
random motion of particles.
• This random motion effect generates heat.
The dielectric polarization provides the energy
to the molecules to rotate into alignment.
• The polarizations (Maxwell-Wagner effect)
contribute heating effect

18. Interfacial polarization
• A combination of the conduction and dipole
polarization mechanism

19. Applications
• It is possible to carry out a number of
microwave organic synthesis. These syntheses
are grouped in the following three categories
 Microwave-assisted reactions in water.
 Microwave-assisted reactions in organic solvents.
 Microwave solvent-free reactions (solid state
reactions).

20. Microwave Assisted Reactions in
Water

21. Hofmann Elimination
• microwave irradiation has led to high-yielding
synthesis of a thermally unstable Hofmann
elimination product. In this water-chloroform
system is used

22. Hydrolysis
• Hydrolysis of Benzyl Chloride
Hydrolysis of benzyl chloride with water in
microwave oven gives 97% yield of benzyl
alcohol in 3 min (Scheme 2). The usual
hydrolysis in normal way takes about 35 min.

23. Oxidation of Toluene
• Oxidation of toluene with KMn04 under
normal conditions of refluxing takes 10-12 hr
compared to reaction in microwave
conditions, which takes only 5 min and the
yield is 40%

24. Oxidation 0f Alcohols
• A number of primary alcohols can be oxidised
to the corresponding carboxylic acid using
sodium tungstate as catalyst in 30% aqueous
hydrogen peroxide.

25. • Thiols have been oxidised to disulphides on
mineral supports like silica, celite, florisel,
alumina

26. Microwave-Assisted Reactions in
Organic Solvents
• Esterification: Reaction of Carboxylic Acid and
Alcohol
A mixture of benzoic acid and n-propanol on
heating in a microwave oven for 6 min in
presence of catalytic amount of cone.
sulphuric acid gives propylbenzoate

27. Orthoester Claisen Rearrangement
• A mixture of allyl alcohol, triethyl orthoacetate
and propanoic acid is heated in a sealed tube
for 48 hr. However, under microwave
conditionslO a mixture of allyl alcohol, triethyl
orthoacetate and propanoic acid in dry
dimethylformamide is heated in microwave
oven for 10 min. The product is obtained in
83% yield

29. Fries Rearrangement
• a mixture of p-cresyl acetate and anhydrous
aluminium chloride are heated in dry
chlorobenzene in a sealed tube in a
microwave oven for 2 min to give9 85% yield
of the product

31. Microwave Solvent Free Reactions
(Solid State Reactions)