Ultrasound in synthetic organic chemistry

An Organocatalyzed and Ultrasound Accelerated Expeditious Synthetic Route to 1,5-Benzodiazepines under Solvent-Free Conditions

“…The creation of the so-called hot spots in the reaction mixture produces intense local temperatures and high pressures generated inside the cavitation bubble and its interfaces when it collapses. [4][5][6][7] The collapse of cavitation bubbles result in the formation very reactive chemical species having short lifetime which facilitates the rapid synthesis of 1,5-benzodiazepines.…”

“…One of the most promising features of this technique is that the assistance of ultrasonic irradiation efficiently shortens the reaction times and the driving force behind this is the phenomenon of acoustic cavitation. 4 Ultrasound irradiations also keep the potential to facilitate organic transformations at ambient conditions by eliminating the need of drastic conditions such as temperature, pressure and concentrations. 5 Furthermore, considering the basic green chemistry concepts, ultrasound is proving to be more efficient for improving the traditional reactions that require expensive reagents, strong acidic conditions, longer reaction time, high temperatures, unsatisfactory yields and incompatibility with other functional groups.…”

A one-pot three-component synthesis of 4,6-diarylpyrimidin-2(1H)-ones (DAPMs) using atomized sodium in THF under sonic condition

“…The reactions carried out under the influence of ultrasound are considered to be clean and the method is green as it involves use of an energy efficient technique [30,31]. The present reaction is an example of a three-phase system: the liquid phase (reagents in solvents), solid phase (atomized sodium and solid substrates), and the gas phase (dissolved gases in the liquids and gases on the inner-surface of the vessel) [31].…”

“…When sound waves pass through liquid medium, they induce vibrational motion to the medium, the solvent molecules then compress, stretch and oscillate around their mean position due to time-varying pressure, at a point when the intensity of the sonic waves is higher enough to break the intermolecular forces existing between the solvent molecules it breaks down and a cavity is formed. The process of generating cavitational bubble is called acoustic cavitation [30,32]; and the bubble collapse then becomes non-spherical near the solid surface i.e., near the surface of the solid atomized sodium and the surface of the vessel, which drags the liquid high-speed jets near the surface creating shockwaves which can activate the surface of the metal. The formation of the micro-jets and shockwaves create the localized erosion responsible for most of the sonochemical effects in the present heterogeneous reaction.…”

Effects of Ultrasound and Microwaves on Selective Reduction: Catalyst Preparation and Reactions

“…For heterogeneous systems proceeding via ionic intermediates, the reaction is influenced primarily through the mechanical effects of cavitation such as surface cleaning, particle size reduction and improved mass transfer. [40,97,98] Here the role of US should be more or less similar to that of high-speed stirrers. [16] The mechanical effect originates from the asymmetric collapse of cavitation bubbles near the liquid-solid phase boundary disrupting the interface and impelling jets of liquid into the catalyst surface (liquid jet impingement), [21,99] leading to the grinding of solid catalysts to become smaller particles, revealing new, previously unexposed surface and therefore, resulting in a dramatic increase in surface area, dispersion and BET surface area.…”