Almost twenty years have passed since the first attempts to run organic syntheses in domestic multimode microwave ovens. Today the market offers a number of dedicated monomode instruments, which allow accurate MW focussing on the reaction vessel, power and temperature control, thus providing the highest degree of reproducibility of the experimental procedures.1 Nevertheless, modified domestic ovens are still very appealing for their low cost, especially for researchers who don’t use microwaves routinely in their synthetic work. Here an inexpensive homemade electronic controller, which can be easily interfaced with any microwave cooker, is described. With this device it is possible to produce microwave pulses of fixed power (depending on the magnetron characteristics) and variable length, according to a programmable “on/off” pattern. Temperature control can be accomplished through a Teflon-lined MW-shielded diode probe especially designed for this purpose, which can be dipped in the reaction medium and, differently from bulky shielded thermocouples, can fit also small reaction vessels. The controller allows temperature monitoring during the “off” periods and can be programmed to block any further MW emission after a certain temperature has been reached, and until it has not dropped under a given value. It should be clear that this system is not supposed to compete with the commercial laboratory ovens equipped with fibre-optic sensors in terms of accuracy of temperature monitoring and thermostatization; it rather represents an interesting tool for those who are looking for an economically convenient way to improve the reproducibility of their syntheses with respect to a common domestic MW cooker.
A simple controller for domestic microwave ovens
TOSCO, Paolo
2005-01-01
Abstract
Almost twenty years have passed since the first attempts to run organic syntheses in domestic multimode microwave ovens. Today the market offers a number of dedicated monomode instruments, which allow accurate MW focussing on the reaction vessel, power and temperature control, thus providing the highest degree of reproducibility of the experimental procedures.1 Nevertheless, modified domestic ovens are still very appealing for their low cost, especially for researchers who don’t use microwaves routinely in their synthetic work. Here an inexpensive homemade electronic controller, which can be easily interfaced with any microwave cooker, is described. With this device it is possible to produce microwave pulses of fixed power (depending on the magnetron characteristics) and variable length, according to a programmable “on/off” pattern. Temperature control can be accomplished through a Teflon-lined MW-shielded diode probe especially designed for this purpose, which can be dipped in the reaction medium and, differently from bulky shielded thermocouples, can fit also small reaction vessels. The controller allows temperature monitoring during the “off” periods and can be programmed to block any further MW emission after a certain temperature has been reached, and until it has not dropped under a given value. It should be clear that this system is not supposed to compete with the commercial laboratory ovens equipped with fibre-optic sensors in terms of accuracy of temperature monitoring and thermostatization; it rather represents an interesting tool for those who are looking for an economically convenient way to improve the reproducibility of their syntheses with respect to a common domestic MW cooker.
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