Development of Coaxial Type flow microwave reactor and application to microwave reactions.

We have developed a flow microwave reactor with a coaxial cavity. It comprises a cylindrical cavity of 100 mm inside diameter, a metal rod along its center axis, and a spiral glass tube for flowing solvents and reactants, as shown in Fig.1. When the input port of microwave is placed at the end of the metal rod, the TEM mode is excited in the cylindrical chamber due to the presence of the metal rod. Simulations of the electric field and the magnetic field within the coaxial cavity are shown in Fig.2. This configuration was confirmed suitable for rapid and continuous microwave syntheses of various functional metal complexes. Experimental results are presented of Ir(Ⅲ) complexes for OLED dopants and Ru(Ⅱ) complexes for various sensors. The application to rapid and continuous microwave synthesis of various functional metal complexes were performed in success. In the similar manner as the coaxial reaction chamber of 2.45GHz, a coaxial reaction chamber for 5.8GHz IMS band, dimension of 51mm in diameter and 50mm in height, is designed The electric field distributions in the chamber and the temperature profiles of solvent are simulated using the commercial simulator (COMSOL Multiphysics) for 5.8 GHz, 5W microwave input. Using the simulation results appropriate dimensions of the chamber are determined for the 5.8 GHz operation. When water is used as a solvent the simulation shows that the temperature rises from20℃ to 95℃ after 300 seconds of the microwave irradiation.

Ultra-rapid microwave synthesis of Li3−x−yMxN (M = Co, Ni and Cu) nitridometallates

Phase-pure ternary lithium nitrides with demonstrable Li+ ion vacancy concentrations can be synthesised by low power microwave reactions in times reduced by orders of magnitude over conventional heating approaches; the electrochemical performance of the materials has been determined.

A New Route for the Synthesis of Quinazolinones

Quinazolinone derivatives are highly bioactive heterocyclic compounds with wider range of microbial activities such as anti-malarial, anti-cancer, anti-inflammatory, anti-hypertensive, anti-convulsant, anti-HIV, etc. Solid supported microwave synthesis of some 3-substituted-4-(2H)-quinazolinones has been carried out by the reaction of anthranilic acid, formaldehyde and primary aromatic amines. The usage of hazardous reagents and organic solvents has been avoided. The reactions were conducted in presence of acidic alumina where formaldehyde entered into cycloaddition to yield the quinazolinone derivatives. The reactions completed within 2-4 minutes with 82-94% of yields in microwave reactions while it took 5-7 hours for completion affording only 56-68% of the yields in conventional reactions. The synthesized quinazolinone derivatives showed moderate to promising antibacterial and antifungal activities.DOI: http://dx.doi.org/10.3126/njst.v12i0.6491 Nepal Journal of Science and Technology 12 (2011) 133-138

New Thermal Routes to ortho-Benzyne

There is experimental evidence that intermediate ortho-benzynes can be made by intramolecular [2 + 4] cycloaddition of a 1,3-diyne with an alkyne. Computations by several groups support a concerted mechanism for the cycloaddition of butadiyne with acetylene. High temperature benzyne cycloreversion has also been demonstrated experimentally; this may in fact be a common reaction in hydrocarbon fuel combustion. Following leads from earlier pyrolysis experiments, herein we predict that cycloaddition of benzyne with butadiyne can proceed by a stepwise mechanism to 2,3-naphthyne. However, a slightly lower energy path leads to a benzocyclobutadiene. ortho-Benzyne can be generated by solution-phase and solid-phase reaction in a microwave reactor. We have developed the method of microwave flash pyrolysis (MFP) for high temperature solid-phase microwave reactions. MFP reaction of phthalic anhydride, a classic benzyne precursor, results in a typical suite of products expected from a relatively high concentration of benzyne.