Microwave-enhanced tritiation reactions

The benefits of using ionic compounds in microwave-enhanced reactions led us to explore the possibility of using ionic solvents i.e. ionic liquids, as donors for both deuterium and tritium. Whilst D20 is now relatively inexpensive and available at high isotopic enrichment, tritiated water is usually employed, for safety reasons, at low isotopic incorporation (we typically use HTO at 5 or 50 Ci mLT1 specific activity corresponding to 0.2-2% isotopic incorporation). This is a serious limitation when there is a need to provide compounds at high specific activity. 

Ease of separation of tritiated products from a reaction medium is an important feature in the choice of labeling procedure. Sometime ago we used polymer-sup-ported acid and base catalysts [12, 13] to good effect and with the current interest in Green Chemistry one can expect to see more studies where the rate accelerations observed under microwave-enhanced conditions are combined with the use of solid catalysts such as Nafion, or zeolites. 

As of now no details of the synthesis of optically active tritiated compounds produced under microwave-enhanced conditions have been published. Another area of considerable interest would be the study of solvent effects on the hydrogenation of aromatic compounds using noble-metal catalysts as considerable data on the thermal reactions is available [52]. Comparison between the microwave and thermal results could then provide useful information on the role of the solvent, not readily available by other means. 

As previous examples have shown the development of microwave-enhanced labeling technology means more than accelerating reactions - it provides alternative opportunities. It follows therefore that some previously used methods now become much more attractive and this is the case for certain aromatic decarboxylations which can now be used for tritiations as well as in the treatment of tritiated waste. In previous studies [69] of the reaction the overriding feature was the harsh experimental conditions required. 

Recently microwaves have been used to greatly accelerate the rates of many of these reactions whilst the development of microwave-enhanced solid state tritiation procedures offers considerable potential. 

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