Activation of Cycloolefin Metathesis by Ultrasonic Irradiation

Ultrasound, an efficient and virtually innocuous means of activation in synthetic chemistry, has been employed for decades with varied success. Not only can this high-energy input enhance mechanical effects in heterogeneous processes, but it is also known to induce new reactivities leading to the formation of unexpected chemical species. What makes sonochemistry unique is the remarkable phenomenon of cavitation, currently the subject of intense research which has already yielded thought-provoking results. This critical review is aimed at discussing the present status of cavitational chemistry and some of the underlying phenomena, and to highlight some recent applications and trends in organic sonochemistry, especially in combination with other sustainable technologies. (151 references.).

Ceramic hollow spheres of MoS2 and MoO3 were obtained by sonochemical synthesis of MoS2 and MoO3 templated on silica nanoparticles (diameters 50-500 nm) followed by acid etching to remove the silica core. The resulting hollow materials have been characterized by elemental analysis, XPS, SEM, TEM, optical absorption, and hydrodesulfurization (HDS) studies. The TEM studies on the hollow ceramic materials indicate the formation of dispersed free spheres with a hollow core. The hollow materials obtained from thermally treated MoS2/SiO2 (450-700 degrees C) show the formation of layered MoS2 (lattice fringes approximately 6.2 A) with a wall thickness of 6-8 layers. The MoS2 hollow spheres are extremely active catalysts for the HDS of thiophene. Hollow spheres of MoO3 are prepared in a similar fashion. Surprisingly, upon heating, hollow crystals of MoO3 with sharp-edged truncated cubes containing inner voids are formed from the initial spheres.