The production of fine chemicals requires efficient synthetic protocols characterized by high regio-, chemo- and stereoselectivity, the activation of poorly reactive substrates and side products formation to be kept to a minimum. A reduction of catalyst loading is also mandatory to avoid the risk of metal or ligand contamination in the final product. A way to achieve this goal is to resort to heterogeneous catalysis using solid or supported catalysts (1), and so minimize the amounts of transition metal that are present in solution. To this end high-intensity ultrasound (US) can play a fundamental role owing to its ability to activate catalysts and disperse them in the system. In the last few years the development of synthetic protocols employing microwave (MW) (2) and US (3) has determined an epoch-making change in organic synthesis. These techniques can dramatically speed up organic reactions and activate poorly reactive substrates. Both are providing new answers to the stringent imperative to decrease the output of industrial waste and to develop clean technologies, e.g. the possibility of carrying out reactions without solvents under MW or in heterogeneous systems under US (4). In these ways they can greatly contribute to a program of sustainable chemistry through the use of less toxic solvents and reagents, the gains in selectivity and energy savings. This program overlaps the application domain of the most versatile among green solvents, namely the room-temperature ionic liquids (RTILs), whose synthesis itself can be efficiently promoted under US (5) and/or MW irradiation (6). Combined irradiation with US and MW is a very promising innovation. Especially in heterogeneous catalysis, additional effects are to be expected when the large amount of energy released by cavitational collapse (causing particle fragmentation and molecular excitation) is associated with MW dielectric volumetric heating. This combination of energy sources can promote or improve a number of chemical processes such as synthesitic reactions, extraction of natural matrices and sample preparation for chemical analysis. Because of technical hurdles it has not been systematically investigated as yet (7). In the synthesis of fine chemicals we can exploit US or MW alone in "relay race", choosing the appropriate technique for each single step; or use both of them in "tandem" in combined reactors (Fig 1). Results, type of collaboration and synergy within the working group will be discussed.

References

1. W. Bonrath, Ultrasonics Sonochem. 2005, 12(1-2), 103-6.

2. A. Loupy, Microwaves in Organic Synthesis, Wiley-VCH, 2002.

3. G. Cravotto, P. Cintas, Chem. Soc. Rev. 2006, 35, 117-200.

4. T. Thiemann, et al. New J. Chem. 2006, 30(3), 359-69.

5. J.M. Leveque, et al. 2006, 13, 189-93.

6. A. Loupy, et al. Eur. J. Org. Chem., 2004, 1112-16.

7. G. Cravotto, et al. Tetrahedron Lett. 2005, 46, 2267-70.

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