Ultrasound Assisted Green Synthesis

The word ultrasound has become common knowledge due to the widespread use of ultrasound scanning equipments in medical applications. Ultrasound refers to sound waves having frequencies higher than those to which the human ear can respond (p, 16 KHz) (Hz = Hertz = cycles per second). High frequency ultrasound waves are used in medical equipments. The ultrasound frequencies of interest for chemical reactions (about 20-100 KHz) are much lower than those used for medical applications, but the power used is higher. 

The term sonochemistry is used to describe the effect of ultrasound waves on chemical reactivity. A number of reviews on the chemical applications of ultrasound have been published. 

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Goharshadi EK, Ding Y, Jorabchi MN, Nancarrow P (2009) Ultrasound-assisted green synthesis of nanocrystalline ZnO in the ionic liquid [hmim][NTf2]. Ultrason Sonochem 16 120-123... 

Eftekhari-Sis, B. and Vahdati-Khajeh, S. 2013. Ultrasound-assisted green synthesis of pyrroles and pyridazines in water via three-component condensation reactions of arylglyoxals. Curr. Chem. Lett. 2 85-92. 

Ultrasound Assisted Green Synthesis 85 is done in dioxane (Scheme 30). 

Zhang, Y., et ah, Green and controlled synthesis of Cu20-graphene hierarchical nanohybrids as high-performance anode materials for lithium-ion batteries via an ultrasound assisted approach. Dalton Transactions, 2012. 41(15) p. 4316-4319. 

Peng, Y., Song, G. Combined microwave and ultrasound assisted Williamson ether synthesis in the absence of phase-transfer catalysts. Green Chem. 2002, 4, 349-351. 

ZnO-CuO hybrid nanoparticles were used as a catalyst for cycloaddition reactions between azides (19) and aUcyne (20) under ultrasound-assisted conditions to afford substituted triazole derivatives (21) (Park et al. 2012) (Scheme 9.5). A green and efficient ZnO nanoparticle-catalyzed synthesis of (/w-isoquinolinones (26) from 3-substimted isocoumarins (24) and heptadiamines (25) is also reported in the literature (Scheme 9.6) (Krishnakumar et al. 2012). The 3-substituted isocoumarins (24) required were synthesized from homophthalic acid (22) and various acid chlorides (23). Khazaei et... 

Bandyopadhyay D, Mukheijee S, Granados JC, Short JD, Banik BK (2012) Ultrasound-assisted bismuth nitrate-indueed green synthesis of novel pyrrole derivatives and their biological evaluation as anticancer agents. Eur J Med Chem 50 209-215... 

H. Naeimi, Z.S. Nazifi, A facile one-pot ultrasound assisted synthesis of 1,8-dioxooctahydroxanthene derivatives catalyzed by Bronsted acidic ionic liquid (BAIL) under green conditions, J. Ind. Eng. Chem. 20 (2014) 1043-1049. 

Figure 5.1 Examples of traditional synthesis methods assisted by "green sources" (microwave and ultrasound) of energy in the synthesis of perovskite ABOj-type oxides.

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