Advantages and disadvantages of solvent-free methods

The following benefits have been reported for microwave-heated reactions under solvent-free conditions7,10  

Deficiencies include a low ratio of organic reactants to solid support and typically a lack of facilities for mixing reactions and for measuring temperature. If the reaction temperature is not known and/or not uniform throughout the sample, reactions may not be reproducible between microwave systems. With variability in operation and performance of domestic microwave ovens, few specific, literature syntheses have been reproduced by others and occasionally such attempts have resulted in alternative outcomes or failure84,85. Some of these deficiencies have been recognised and addressed through the development of specific equipment. 

It is not always acknowledged that solvents are used for dry media reactions, both to load the reactants onto the support and to elute the products after reaction. If the supports are polar materials such as alumina or silica gel, which are commonly used in liquid chromatography, substantial quantities of solvent may be required to remove the organics. For clean processing, recycling of the solvent and the support would be essential. The latter does not appear to have been demonstrated and may prove difficult 

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