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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