Study type: Medical/biological study (experimental study)

Nonthermal microwave effects revisited: on the importance of internal temperature monitoring and agitation in microwave chemistry. med./bio.

Published in: J Org Chem 2008; 73 (1): 36-47

Aim of study (acc. to author)

In order to study the existence of nonthermal effects of microwaves, four synthetic transformations (Diels-Alder cycloaddition, alkylation of triphenylphosphine and 1,2,4-triazole, direct amide bond formation) were reevaluated under both microwave dielectric heating and conventional thermal heating.

Background/further details

In all four transformations, previous studies (see "related articles", especially Loupy 2004, Cvengros 2004, Loupy 2001, and Iannelli 2005) have claimed the existence of nonthermal effects of microwaves in these reactions, i.e. significant differences in conversion and/or product distribution were found comparing the conventionally and microwave-heated experiments performed at the same measured reaction temperature.
A specialized fiber-optic temperature probe was used that allowed simultaneous temperature detection at different positions of the reaction mixture.
Description of general experimental procedures, images, and heating profiles for reactions is available free of charge at http://pubs.acs.org.

Endpoint

Exposure

No exposure details are available.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • during exposure

Main outcome of study (acc. to author)

The critical reevaluation of all four reactions has provided no evidence for the existence of nonthermal effects of microwaves. Ensuring efficient agitation of the reaction mixture via magnetic stirring, no significant differences in terms of conversion and selectivity between experiments performed under microwave or oil bath conditions at the same internally measured reaction temperatures were found. The observed effects were purely thermal and not related to the microwave field.

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