Microwave Chemistry
Microwaves are 0.3 to 300 GHz electromagnetic radiation. To avoid interference with communication networks, all microwave heaters (domestic or scientific) are designed to work at either 2.45 GHz or 0.9 GHz, the former beingmore prevalent. According to Planck’s law, the energy at this wavelength is 0.3 cal/mol, and is therefore insufficient for molecular excitation. Thus most of the microwave energy heats the substrate rather than inducingany special reactions. This heating is different from conventional heating, in which heat is transferred by conduction, convection,or radiation. In microwave heating, electromagnetic energy is transformed into heat by ionic conduction and the friction due to rapid dipole reorientation. The larger the dipole moment of a molecule, the more vigorous is the oscillation in the microwave field, resulting in more heating. This type of heating is fast, has no inertia, and is in-situ without heating the surroundings.
Chemistry under microwave radiation is quite different, fast,and efficient (Gedye et al., Tetrahedron Lett., 27 (1986) 279; Giguere et al., Tetrahedron Lett., 27 (1986) 4945; Loupy et al., Chimie, 7 (2004) 103-112). It reduces the need for solvents and is eco-friendly. It has been used in hetero-cyclic, organometallic, and combinatorial chemistry. Advantages are rapid reactions under controlled temperature and pressure (especially in a closed system), achievement of higher-purity products owingto short residence times at higher temperatures, and better yields at even very short residence times. Another important factor is that during dipolar polarization under microwave radiation, the activation parameters are modified. For example, it has been reported by Lewis that during imidization of polyamic acid, the activation energy is reduced from 105 to 57 KJ/mol. (Lewis et al., J. Polym. Sci., 30A (1992) 1647)
Mitra and Iqbal, US Patent 7,754,054, (7/13/2010)
Microwave Assisted Grafting
Microwave assisted Polymerization
Reactions
Recent US Patents
Recent Journal Articles
Glycolysis of polycarbonate wastes with microwave irradiation
Polimery #5 (2011)
Nikje. Poland, glycolized polycarbonates from waste compact discs with ethylene glycol using microwave irradiation in the presence of sodium hydroxide as catalyst in order to obtain bisphenol A (BPA) as the sole product. (RDC 6/1/2011)
Modification of Rice Straw for Heavy Metal Ion Adsorbents by Microwave Heating
(pages 100–106) Macromolecular Symposia 296 #1 (2010)
Rungrodnimitchai of Thammasat University, Thailand modified the cellulose in rice straw by phosphorylation using conventional heating or microwave heating. This modified rice straw could remove 90% of Cd2+and Cr3+in 60 minutes and remove 99% of Pb2+after 30 min.
Factorial design to optimize microwave-assisted synthesis of FDU-1 silica with a new triblock copolymer
(1-9) Microporous and Mesoporous Materials 133. #1-2 (2010)
Cides da Silva et al formed silica with large cage-like mesopores prepared by heating a new triblock copolymer Vorasurf 504® (EO)38(BO)46(EO)38 in ethanol with microwaves resulting in an cubic mesoporous silica. (RDC 11/2/2010)