MICROWAVE INDUCED HETEROCYCLIC
COMPOUND SYNTHESISSUBHRADIP ROYCHOWDHURY* & SATARUPA BHATTACHARJEE**
*M.PHARM [PHARMACEUTICAL CHEMISTRY] DEPT. OF PHARM. SC.
BIRLA INSTITUTE OF TECHNOLOGY, MESRA-835215
** B.PHARM 4TH YEAR GURU NANAK INSTITUTE OF PHARMACEUTICAL SCIENCE AND TECHNOLOGY, KOLKATA-114
WHAT IS MICROWAVE
Microwave is an electro magnetic wave.
It has a wavelength of 10-3 m and a frequency of 1011 HZ.
The penetration power of microwave is poor.
It can generate heat in the applied field.
MICROWAVE INDUCED SYNTHESIS IS ADVANTAGEOUS OVER THE
CONVENTIONAL PROCESSES
Conventional methods : Longer heating time, elaborate and tedious procedures , excessive use of solvents hence higher cost and environmental pollution.
Pharmaceutical chemistry laboratories : Use of large quantities of toxic chemicals and solvents cause hazards.
Microwave assisted organic synthesis : Environmentally friendly processes known as GREEN CHEMISTRY.
GENERAL PRINCIPLE BEHIND THE MICROWAVE ASSISTED SYNTHSIS
Rate increase is a purely thermal/kinetic effect.
High reaction temperature is quickly attained due to irradiation of polar materials in a microwave field.
Microwave energy reduces the total reaction time by reducing both the heat-up and cool-down time.
Here reagents are pre-adsorbed either onto a essentially microwave transparent ( silica, alumina or clay) or strongly absorbing (graphite) inorganic support.
MECHANISMS OF MICROWAVE ASSISTED SYNTHESIS
DIPOLARIZATION
MICRO WAVE
FREQUENCY TO A CERTAIN
FIELD
POLARITY OF FILED
IS CHANGED
POLAR MOLECUL
ES CHANGE THEIR
POSITIONS TO KEEP
WITH CHANGIN
G POLARITY OF SAME FIELD
RANDOM MOTION OCCURS
GENERATION AND CHANGE
IN ENERGY DUE TO
COLLISIONS
OHMIC HEATING
INTERFACIAL POLARIZATIONMICROWAVE IS APPLIED
OVER METAL
PARTICLES DISPERSED
IN DELECTRIC SILICONE MATRICES
(INSULATING
MATERIAL)
SURFACES OF METALIC PARTICLES BECOME
POLARIZED
CONTACT WITH
DIELECTRIC MATRIX CAUSES
REDUCTION IN
POLARIZATION OF
PARTICLE
POLARIZATION OF FILED DOESN’T OCCUR
INSTATANEOUSLY & REMAINS
BEHIND APPLIED FILED
DISSIPATION OF FIELD
CAUSES HEATING
INFLUENCE OF APPLIED ELECTRIC (MICRO WAVE) FIELD
HEAT GENERATIO
N
CURRENT IS INDUCED THROUGH ELECTRIC (OHMIC)
RESISTANCE
POLARIZATION
CONDUCTIVITY
SPECIES,IONS,
ELECTRONS MOVE
THROUGH MATERIAL
BENZAMIDE SYNTHESIS:
It was the first reaction in synthetic chemistry that was studied under the influence of microwave radiation.
PYRROLE SYNTHESIS :
BENZIMIDAZOLE / OXAZOLE / THIAZOLE SYNTHESIS :
SELECTIVE ALKYLATION OF A HETEROCYCLE
(NUCLEOPHILIC SUBSTITUTION) :
Selectivity is achieved in the N-alkylation of 1,2,4-triazole under microwave as only N1-alkyl derivative was formed whereas conventional condition gives di-1,4-substituted compound.
CONCLUSION
Microwave can be used to synthesize mono and polynuclear heterocyclic moieties.
Saving of time and reagent ,hence a good future to the synthetic chemistry.
Less complicated,cost effective and cheaper than other chemical methods.
REFERENCES
Rajasekhar K.K. et al; COMPARATIVE STUDY OF CONVENTIONAL AND MICROWAVE INDUCED SYNTHESIS OF SELECTED HETEROCYCLIC MOLECULES; International Journal of Chetek Research; ISSN : 0974-4290;Vol.2, No.1, pp 592-597, Jan-Mar 2010
Katritzky A.R., Singh S.K.; Microwave-assisted heterocylic synthesis , Center for Heterocyclic Compounds, Department of Chemistry,University of Florida, Gainesville, FL 32611-7200
Kingston, H. M.; Haswell S. J. (Eds.) Microwave- Enhanced Chemistry. Fundamentals, Sample preparation and Applications, American Chemical Society, Washington DC, 1997.
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