Synthesis of biologically active iminosugars using unconventional methods - microwave and ultrasonic irradiation
Microwave heating in the laboratory can be traced back to the 1950’s.
Microwaves have wavelength in the range of 1mm to 1 m, corresponding to frequencies between 30 and 3 GHz. Telecommunications and microwave radar equipments occupy many of the band frequencies in this region. Hence, the microwave frequencies for industrial and scientific purposes are imposed by international convention the most routinely used being 2.45 GHz (wavelength of 12.2 cm).
Typically, some reactions that do not occur by classical heating, or that lead to very low yields can be performed in good yields under microwave irradiation. Some authors suggest the existence of a specific effect derived from the microwave field, recognized as “microwave effect”, and not from the rapid heating.
The benefits of microwave over conventional heating are acceleration of reaction rate, milder reaction conditions, higher chemical yield, lower energy usage, different selectivities.
Microwave activation under controlled conditions has been shown to be an invaluable technology for medicinal chemistry and drug discovery applications since it often reduces dramatically the reaction time (from days to minutes). This can also have a positive effect on the yield and selectivity especially in the conversion of carbohydrates in which long reaction times of the classical methods lead to degradations of the starting material.