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Sonocatalysis and Basic Clays. Michael Addition Between Imidazole and Ethyl Acrylate

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Abstract

Under ultrasound activation, imidazole was condensed with ethyl acrylate using two basic clays (Li+ and Cs+ montmorillonites). The clay catalysts were characterized by chemical analyses, nitrogen adsorption isotherms, and X-ray diffraction. Under sonochemical conditions N-substituted imidazole can be obtained with a high activity and selectivity. The conversion increases with the basicity of the clays and the ultrasonic exposition time. The yield presents a maximum for 0.1 g of Cs+ montmorillonite after 60 min of sonication.

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... Brønsted acidic basic sites. This effect involves the restoring of HTs/LDHs by the rehydration of their thermally decomposed precursors through contact with solution of appropriate ions (Debecker et al., 2009;Vankudotha et al., 2017;Komadel and Madejova, 2006;Benesi and Winquist, 1979;Martin-Aranda et al., 2002;Lambert and Poncelet, 1997;Moronta, 2004). The strength of basic sites possess by HTs/LDHs can be measured through the CO 2 -TPD (temperature programmed desorption), formic acid adsorption, while the acidic strength also measured by NH 3 -TPD, pyridine, heat of adsorption or desorption temperature methods (Vankudotha et al., 2017;Abdellattif and Mokhtar, 2018;Wang et al., 2017c). ...
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Background Nowadays people demand for healthy, convenient, and wholesome foods. Double emulsions have attracted widespread attention in the food industry owing to their capability of encapsulating the compounds, fabricating polymersomes, and acting as fat replacers or sweetness enhancers in different foods. Scope and approach In this review, properties and their importance in the fabrication of double emulsions along with their advantages and disadvantages are discussed. In the lateral part of the manuscript, the instability mechanism and the effect of different variables on the stability of the double emulsions are reviewed. Finally, this review provides a glimpse of the recent food application of W/O/W double emulsions. Key findings and conclusions Double emulsions have a better profile on the encapsulation of nutrients along with maintenance of the organoleptic quality of the food. The conventional emulsification techniques result in low encapsulation efficiency and poor monodispersity. With recent developments, different novel methods for the fabrication of double-emulsions have been developed such as glass capillary microfluidic devices, membrane emulsification, phase inversion techniques, etc. However, findings thus far indicate that the long-term stability of double emulsions remains a crucial issue that limits their wide application in food formulations. Therefore, further research should focus on finding innovative approaches to improve the stability of double emulsions.
... The interaction takes place through the intermediate phenomenon of acoustic cavitations. Three important factors have to be considered when an ultrasonic induced reaction is performed: the acoustic field, the bubbles field and the chemical system [8,9]. The chemical effects of ultrasounds have been attributed to implosive collapse of the cavitations period of the sound waves. ...
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In the present paper, we have executed the synthesis of substituted 5-(2-chloroquinolin-3-yl)-3-phenyl-4,5-dihydroisoxazolines via the reactions of substituted 3-(2-chloroquinolin-3-yl)-1-phenylprop-2-en-1-ones with hydroxylamine hydrochloride and sodium acetate in aqueous acetic acid solution in 72-90% yields at room temperature under ultrasound irradiation. This method provides several advantages such as operational simplicity, higher yield, safety and environment friendly protocol. The resulting substituted isoxazolines were characterized on the basis of (1)H NMR, (13)C NMR, IR, elemental analysis, and mass spectral data.
... Brønsted acidic basic sites. This effect involves the restoring of HTs/LDHs by the rehydration of their thermally decomposed precursors through contact with solution of appropriate ions (Debecker et al., 2009;Vankudotha et al., 2017;Komadel and Madejova, 2006;Benesi and Winquist, 1979;Martin-Aranda et al., 2002;Lambert and Poncelet, 1997;Moronta, 2004). The strength of basic sites possess by HTs/LDHs can be measured through the CO 2 -TPD (temperature programmed desorption), formic acid adsorption, while the acidic strength also measured by NH 3 -TPD, pyridine, heat of adsorption or desorption temperature methods (Vankudotha et al., 2017;Abdellattif and Mokhtar, 2018;Wang et al., 2017c). ...
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Hydrotalcite-like anionic clays (HTs) also known as Layered double hydroxides (LDHs) have been developed as multifunctional materials in numerous applications related to catalysis, adsorption, and ion-exchange processes. These materials constitute an important class of ionic lamellar solid clays of Brucite-like structure which comprise of consecutive layers of divalent and trivalent metal cations with charge balancing anions and water molecules in interlayer space. These materials have received increasing attention in research due to their interesting properties namely layered structure, ease of preparation, flexible tunability, ability to intercalate different types of anions, electronic properties, high thermal stability, high biocompatibility, and easy biodegradation. Moreover, HTs/LDHs have unique tailorable and tuneable characteristics such as both acidic and basic sites, anion exchange capability, surface area, basal spacing, memory effect, and also exhibit high exchange capacities, which makes them versatile materials for a wide range of applications and extended their horizons to diverse areas of science and technology. This study enlightens the various rational researches related to the synthetic methods and features focusing on synthesis and/or fabrication with other hybrids and their applications. The diverse applications (namely catalyst, adsorbent to toxic chemicals, agrochemicals management, non-toxic flame retardants, and recycling of plastics) of these multifunctional materials related to a clean and sustainable environment were also summarized.
... The Michael reaction of chalcones as acceptors with various active methylene compounds such as diethyl malonate, nitromethane, cyclohexanone, ethyl acetoacetate and acetylacetone as donors catalyzed by KF/basic alumina results in adducts in high yield within a shorter time under ultrasound irradiation (Scheme 65) [101]. Under ultrasound activation, imidazole was condensed with ethyl acrylate using two basic clays (Li + and Cs + montmorillonites) [102] ...
... Martin-Aranda et al. [42] in 2002 took the advantage of sonication reaction and developed a novel methodology for the synthesis of N-substituted imidazole derivatives 21 by the Michael addition of imidazole 7 to ethylacrylate 20 catalysed by basic clays (Li + and Cs + montmorillonites). Alkaline clays are active and very selective catalyst under sonication and employs positive effect for Michael addition of imidazole to ethyl acrylate also enhances the formation of N-substituted imidazole derivatives in comparision to other conventional thermal heating reactions. ...
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Introduction Aza-Michael addition is an important reaction for carbon-nitrogen bond formation in synthetic organic chemistry. Expalantion Conjugate addition of imidazole to α,β -unsaturated carbonyl/cyano compounds provides significant numbers of the biologically and synthetically interesting products, such as β -amino acids and β -lactams, which have attracted great attention for their use as key intermediates of anticancer agents, antibiotics and other drugs. Conclusion This review addresses most significant method for the synthesis of N-substituted imidazole derivatives following Michael addition reaction of imidazole to α,β -unsaturated carbonyl/cyano compounds using ionic liquid/base/acid/enzyme as catalysts from year 2007-2017.
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... In case of aluminosilicates, low frequencies ultrasonic irradiation significantly shortens the time of nucleation and synthesis [6][7][8], enhances accessibility of internal pores of aluminosilicates, reduces time of adsorption equilibrium [9,10] as well as intensifies the intercalation processes [11,12], etc. Besides, short ultrasound irradiation is usually applied during purification of natural clay samples as promoting deagglomeration of clay minerals phases and non-clay admixtures [13,14]. Sometimes, a combined use of clays and ultrasonic irradiation may have a synergetic effect on reaction time and yield of products in several catalytic organic reactions [4,15,16]. However, depending on the choice of ultrasonic parameters (power, frequency, irradiation time, etc), the nature of a solvent or an electrolyte present in dispersion and the type of the structure of aluminosilicate itself, sonication may severely affect properties [17,18] and behavior of aluminosilicate dispersions [19][20][21]. ...
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... These improvements were attributed to the mechanical effects observed under ultrasound. Martín Aranda et al. (2002) did not explain the involved mechanisms but observed a clear improvement of the yield in the Michael addition between imidazole and ethyl acrylate in the presence of basic clays (Li + and Cs + montmorillonites) when the reaction was performed under 40 kHz (550 W, ultrasonic bath), compared to silent conditions. They also showed the efficient use of two other basic clay minerals (Li + and Cs +-exchanged saponites) in the Knoevenagel condensation of carbonylic compounds with malononitriles (synthesis of α,β-unsaturated nitriles) under ultrasonic irradiation (40 kHz, 550 W) to reduce the reaction time ( Martín-Aranda et al., 2005). ...
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Clays are widespread materials of natural origin, possessing various surface active sites, exchangeable and structural cations, as well as micro- and mesoporous structures that allow their application in ion-exchange, adsorption and catalytic processes. A recent trend has been to combine clays to ultrasound irradiations (sonochemistry) in a range of different applications and the results demonstrate significant and occasionally surprising synergetic effects. Indeed, ultrasound can lead to significant changes in the properties and behaviors of clays depending on the choice of ultrasonic parameters. Here, the advantages and limitations of the clay science/sonochemistry combination have been critically highlighted in different applications, to understand how, and in which respects, ultrasound could become an essential and efficient tool of clay chemistry in the future.
... The sonochemical phenomena originate from the interaction between a suitable field of acoustic waves and a potentially reacting chemical system; the interaction takes place through the intermediate phenomenon of acoustic cavitation. Three important factors have to be considered when an ultrasonic induced reaction is performed: the acoustic field, the bubbles field and the chemical system [13,14]. ...
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