Ultrasonics Sonochemistry

Published by Elsevier
Print ISSN: 1350-4177
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Changes in the cavitation intensity of gases dissolved in water, including H2, N2, and Ar, have been established in studies of acoustic bubble growth rates under ultrasonic fields. Variations in the acoustic properties of dissolved gases in water affect the cavitation intensity at a high frequency (0.83MHz) due to changes in the rectified diffusion and bubble coalescence rate. It has been proposed that acoustic bubble growth rates rapidly increase when water contains a gas, such as hydrogen faster single bubble growth due to rectified diffusion, and a higher rate of coalescence under Bjerknes forces. The change of acoustic bubble growth rate in rectified diffusion has an effect on the damping constant and diffusivity of gas at the acoustic bubble and liquid interface. It has been suggested that the coalescence reaction of bubbles under Bjerknes forces is a reaction determined by the compressibility and density of dissolved gas in water associated with sound velocity and density in acoustic bubbles. High acoustic bubble growth rates also contribute to enhanced cavitation effects in terms of dissolved gas in water. On the other hand, when Ar gas dissolves into water under ultrasound field, cavitation behavior was reduced remarkably due to its lower acoustic bubble growth rate. It is shown that change of cavitation intensity in various dissolved gases were verified through cleaning experiments in the single type of cleaning tool such as particle removal and pattern damage based on numerically calculated acoustic bubble growth rates.
 
The combination of ultrasound and electrochemistry -sonoelectrochemistry can produce a variety of effects within an electrochemical system including enhanced mass transport, in situ cleaning of an electrode surface, diminution of the diffusion layer, and possible induction of new reactions by sonochemical enhancement of follow-up reactions post-electron transfer. Herein, we show that ultrasound provides a useful extra dimension to electrosynthesis via a switch in the sonoelectroorganic mechanism in which dimerisation is disfavoured by virtue of convective mixing promoted by insonation. Under 'normal' voltammetric conditions the reduction of 1-iodoadamantane at a silver cathode in tetrahydrofuran (THF) and acetonitrile (ACN) involves a single electron forming a mixture of monomeric and dimeric products; 58%/THF, 50%/ACN adamantane and 39%/THF, 50%/ACN 1,1'-biadamantane, respectively. However, under the conditions of insonation using a 10 kHz transducer, a single product is formed exclusively; 93%/THF, 96%/ACN adamantane. The effect of insonation upon the voltammetry at a silver macroelectrode is shown and compared to that under silent conditions. In addition, the previously observed characteristic series of oxidation and adsorption peaks following reduction of 1-iodoadamantane are reduced in magnitude under insonation. Overall, this work shows that the effect of insonation can switch the mechanism of follow-up chemical processes - favoring the formation of a monomer.
 
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Reaction of 4-chlorobenzylaldehyde and Ac 2 O in the presence of different amount of P(4-VPH)ClO 4 at room temperature under solvent free conditions. a
Poly(4-vinylpyridinium) hydrogen sulfate solid acid was found to be efficient catalyst for preparation of 1,1-diacetate using ultrasound irradiation at ambient temperature and neat condition. Deprotection of the resulting 1,1-diacetates were achieved using the same catalyst in methanol solvent under ultrasound irradiation at room temperature. This new method consistently has the advantage of excellent yields and short reaction times. Utilization of solvent free, simple reaction conditions, isolation, and purification makes this manipulation very interesting from an economic and environmental perspective. Further, the catalyst can be reused and recovered for several times.
 
1,1-Disubstituted-2,6-diarylcyclohexane-4-ones have been synthesized via double Michael addition of 1,5-diaryl-1,4-pentadien-3-one with various active methylene compounds such as dimethyl malonate, diethyl malonate, methyl cyanoacetate and ethyl cyanoacetate catalyzed by KF/basic alumina under ultrasound irradiation to give good yields within a short time.
 
Naphthols were selectively coupled under sonication using Fe(+3) impregnated pillared Montmorillonite K10 and TBHP as an oxidant. Considerable enhancement in the reaction rate was observed under sonication as compared to the reaction performed under silent condition. The activity of catalyst was compared with other Fe clay catalysts. Various parameters like solvent, catalyst and TBHP concentration has been studied. The heterogeneous active catalyst K10-FePLS120 was recycled without loss in activity and selectivity performance.
 
1,1,1-Trichloroethane (TCA), labeled as a priority pollutant by the Environmental Protection Agency (EPA) of China, can be removed from groundwater by sonochemical oxidation. The sonochemical oxidation of TCA in the presence of persulfate (PS) showed a significant synergistic effect. The operational parameters, ultrasonic frequency, PS/TCA molar ratio, radical scavenger, inorganic anions (Cl(-), CO(3)(2-), HCO(3)(-) and NO(3)(-)) and humic acid (HA), were evaluated during the investigation of the sonochemical reaction. The results showed that the degradation of TCA followed pseudo-first-order kinetics, and the rate constant was found to increase with increasing ultrasonic frequency but to decrease with both an increasing PS/TCA molar ratio and an increasing concentration of inorganic anions. With a concentration of 4.46mg/L of HA in solution, an enhanced effect was observed. Further addition of HA retarded the degradation rate of TCA. TCA could be eliminated almost completely by sono-activated persulfate oxidation, with sulfate and hydroxyl radicals serving as the principal oxidants as confirmed by the addition of radical scavengers. Eleven chlorinated degradation intermediates were detected and quantified by purge and trap gas chromatography coupled with mass spectrometry (P&T-GC-MS) in the absence of pH buffer. Three TCA degradation pathways were therefore proposed. In conclusion, the sono-activated persulfate oxidation process appears to be a highly promising technique for the remediation of TCA-contaminated groundwater.
 
The new neutral binuclear lead(II) azido coordination compound, [Pb2(tmph)2(μ-N3)2(CH3COO)2] (1) [tmph=3,4,7,8-tetramethyl-1,10-phenanthroline], has been synthesized by a sonochemical method. Single crystal X-ray structure shows that the overall structure of 1 is binuclear unit. Complex 1 has a bridging azido pathway, end-to-end bridging azides between a pair of lead(II) centers. This is further extended into a one-dimensional (1D) and three-dimensional (3D) supramolecular structure by Pb⋯C and π-π weak directional intermolecular interactions. The coordination number of lead(II) ions is seven, PbN4O3, with two N-donor atoms from tmph ligands and three O-donors from acetate anions and two N-donors from two azide anions. It has a "stereo-chemically active" electron lone pair, and the coordination sphere is hemidirected. The PbO nanoparticles were obtained by thermolysis of 1 at 180°C with oleic acid as a surfactant. The morphology and size of the prepared PbO samples were further observed using scanning electron microscopy (SEM). Copyright © 2014 Elsevier B.V. All rights reserved.
 
NIR fluorescence spectra of PbS QDs in solution phase (blue-solid line) and in silica composite (red-dotted line). On the right is a picture of the vial containing the composite. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
(a-c) TEM images of PbS-A-SWNT where PbS-A are attached to SWNT by sonication (scale bar in (a) À50 nm, (b) and (c) À20 nm, (d) PbS-B-SWNT, where PbS-B are attached to SWNT by sonication (scale bar 20 nm).
(a) Quenching of PbS-A NIR fluorescence as a function of SWNT concentration. (b) Quenching of PbS-B NIR fluorescence as a function of SWNT concentration. The consecutive spectra show emission on addition (and subsequent sonication for 2 min) of 0, 10, 20 and 30 lL of SWNT suspension.
TEM image of PbS QDs synthesized in situ on the surface of single-walled carbon nanotubes. The scale bar is 50 nm.
Lead sulfide (PbS) quantum dots stabilized by 1,2-benzenedimethanethiol can be synthesized by mixing Pb(NO3)2 and Na2S solutions in ethanol under ultrasound irradiation. The PbS quantum dots (2.7 and 3.6nm in diameter) are characterized by their absorption and fluorescence spectra in the near infrared region and by other surface analytical techniques. With addition of single-walled carbon nanotubes (SWNT) to the system, this ultrasound-assisted procedure allows attachment of PbS nanoparticles to SWNT surface via π-π stacking, thus providing a simple one-pot method for preparation of SWNT-PbS nanoparticle composite materials. Using the ultrasound-assisted method for synthesizing silica composites containing PbS nanoparticles by a sol-gel process is also described.
 
The enantioselective hydrogenation of 1-phenyl-1,2-propanedione was carried out over Pt/Al2O3, Pt/SiO2, Pt/SF (silica fiber), Pt/C catalysts modified with cinchonidine under ultrasonic irradiation. The initial rate, regioselectivity and enantioselectivity were investigated for different catalyst pretreatments, solvents and ultrasonic powers. The ultrasound effects were very catalyst dependent. The sonication significantly enhanced enantioselectivity and activity of the Pt/SF (silica fiber) catalyst. For the other Pt supported catalysts the reaction rate, enantioselectivity and regioselectivity increased moderately. The choice of solvent influenced the impact of ultrasound effect, namely in mesitylene, which has the lowest vapor pressure, the highest ultrasound enhancement was observed. The effect of sonication on catalysts surface was studied by transmission electron microscopy and scanning electron microscopy (SEM). No significant change in the metal particle size distribution due to sonication was observed. However, in the case of the Pt/SF catalyst, acoustic irradiation induced morphological changes on the catalyst particle surface (SEM), which might be the cause for enhancement of the initial reaction rate and enantioselectivity.
 
Triethylamine was found to be an efficient catalyst for the synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones by one-pot reaction of phthalhydrazide, aromatic aldehydes, and malononitrile or ethyl cyanoacetate in ethanol under ultrasonic irradiation. The advantages of this method are the use of an inexpensive and readily available catalyst, easy workup, improved yields, and the use of ethanol as a solvent that is considered to be relatively environmentally benign.
 
A comparative study, ultrasound (US) versus microwave (MW) versus conventional thermal heating (TH), for synthesis of isoindolo-1,2-diazine is described. The reaction pathway is fast, efficient and straight applicable, involving a Huisgen [3+2] dipolar cycloaddition of cycloimmonium ylides to 1,4-naphthoquinone. A feasible reaction mechanism for the obtaining of the fully aromatized tetra- and penta- cyclic isoindolo-1,2-diazine is presented. Under US irradiation the yields are much higher (sometimes substantially, by almost double), the reaction time decreases substantially, the reaction conditions are milder. The use of a generator with a higher nominal power induces higher yields and short reaction times. Overall the use of US it proved to be more efficient than MW or TH. A feasible explication for US efficiency is presented.
 
Synthesis of aromatic 1,2-diketones through I 2 /SDS/water system.
We report a convenient, neutral, and facile methodology for the synthesis of aromatic 1,2-diketones from the corresponding oximinoketones in the presence of I2/SDS/water system under ultrasound-assisted conditions. Furthermore, a series of compounds were synthesized and characterized by melting point, IR, NMR, MS, and elemental analysis. Utilization of easy reaction conditions, very high to excellent yields, and short reaction times makes this manipulation potentially very useful.
 
A thorough study concerning O-alkylation and α-bromination of dihydroxyacetophenone (DA) and N-alkylation of 1,2-diazine, under ultrasound (US) and microwave (MW) irradiation as well as under conventional thermal heating (TH) is presented. Under US and MW irradiation the yields are higher, the amount of used solvent decreases substantially, the reaction time decreases considerable (from hours or days to minutes) and the consumed energy decreases, consequently the O-alkylation, α-bromination and N-alkylation methods could be considered environmentally friendly. A selective and efficient way to either bis-O-alkylation or mono-O-alkylation of DA has been found, the relative position of the two hydroxyl groups on the phenyl moiety being compulsory. A selective and efficient way for α-bromination in heterogeneous catalysis of DA derivatives under US irradiation is presented. The N-alkylation reaction of DA under US and MW irradiation proved to be the most convenient setup procedure for these types of reactions. Overall, the use of US proved to be more efficient than MW or TH.
 
Irradiation with ultrasound is found to facilitate the synthesis of 2-alkyl-2-alkoxy-1,2-di(furan-2-yl)ethanone in the presence of tetrabutylammonium bromide (TBAB) as solid-liquid phase transfer catalysis. A higher yields (>70%) and shorter reaction time (<15 min) give this method obvious advantages over the conventional ones.
 
ZnO nanorods have been successfully used as an efficient, economic, and reusable catalyst for the synthesis of imidazo[1,2-a]azine under ultrasonic irradiation. This procedure offers advantages in terms of higher yields, short reaction times and mild reaction conditions.
 
The 1,3-dipolar cycloaddition reaction between 7-(3-azidopropoxy)-5-hydroxyflavone and phenylacetylene was carried out to investigate the synthesis of 7-(3-(4-phenyl-1,2,3-triazol-1-yl)propoxy)- 5-hydroxyflavone in presence of ultrasound (sono-synthesis) and absence of ultrasound (conventional method) under relatively optimized solvent and catalyst conditions. The reaction rate was notably accelerated with the help of ultrasound irradiation. An experiment was especially carried out for investigating the acceleration mechanism of ultrasound on the cycloaddition. A novel series of chrysin derivatives linked with 1,2,3-triazoles were obtained by the copper(I)-catalyzed 1,3-dipolar Huisgen cycloaddition reaction using t-BuOH/H(2)O (1:1 v/v) as reaction solvents and CuSO(4)·5H(2)O/sodium ascorbate as the catalyst at room temperature in the presence of ultrasound irradiation. Their structures are elucidated by NMR, ESI MS, IR and Elemental analysis.
 
Cyanoacetamides 3 were prepared via reacting ethyl cyanoacetate with benzylamine. Yields and reaction times needed for reaction completion at room temperature, by microwaves (muomega) heating and under ultrasound (US) irradiations are compared. The formed cyanoacetamides were coupled with aromatic diazonium salts and the formed arylhydrazones were used as precursors to title triazoles and pyrazoles via reacting the former with hydroxylamine and chloroacetonitrile. Yields of products formed via conventional heating are compared with those of muomega and US irradiation.
 
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The effect of catalysts and ultrasound in the acetylation reaction.
The effect of catalysts and ultrasound in the azidation reaction.
Generalization of the one-pot three-step procedure under ultrasound irradiation.
Cell viability, CML K562 cell line (% inhibition at 0.5 mM, XTT assays).
A simple and efficient synthesis of modified 1,2,3-triazole nucleosides was developed. The strategy involved sequential one-pot acetylation-azidation-cycloaddition procedure and was found to be highly effective under a cooperative effect of ultrasound activation and iron/copper catalysis. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with conventional conditions. This one-pot procedure provides several advantages such as operational simplicity, high yield, safety and environment friendly protocol. The resulting substituted nucleosides were evaluated for their anticancer activity against K562 chronic myelogenous leukemia (CML) cell line.
 
Sonication of aromatic aldehydes, urea and ethyl acetoacetate in presence of solvent (ethyl alcohol) or solvent-less dry media (bentonite clay) supported-zirconium (IV) chloride (ZrCl(4)) as catalyst at 35 kHz gives 6-methyl-4-substitutedphenyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylic acid ethyl esters proficiently in high yields.
 
Dehydrogenation of various 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides (THPMs) to 2-oxo-1,2-dihydropyrimidine-5-carboxamides (DHPMs) using tetrabutylammonium peroxydisulfate (TBAPS) as an efficient oxidizing agent under thermal and sono-thermal conditions has been investigated. In contrast to the thermal reaction, a decrease of the amount of oxidant and an increase of the rate of reaction are observed by simultaneously applying heat and ultrasound. The nature of both C-4 and C-5 substituents on the heterocyclic ring influences the rate of reaction under both conditions. The proposed electron-transfer-induced dehydrogenation in this study is supported by conductometric studies.
 
The alternative synthesis of 12 1,2,4-oxadiazoles using ultrasound irradiation from trichloroacetoamidoxime and acyl chlorides is reported. Seven of them are novel compounds. The 3-trichloromethyl-5alkyl(aryl)-1,2,4-oxadiazoles have been synthesised in better yields and shorter reaction times compared to the conventional method. This protocol can be applicable for preparation of 1,2,4-oxadiazoles containing aryl or alkyl groups attached at their C-5 side-chain.
 
Optimization reactions for obtaining compound 3a.
Synthesis of compounds 3a-h.
Optimization reaction for compound 5a.
Synthesis of compounds 5a-l.
Ultrasonic irradiation was used in the synthesis of a series of novel 1,2,4-triazolo[1,5-a]pyrimidines. The products were synthetized from the cyclocondensation reaction of 1,1,1-trifluoro-4-metoxy-3-alken-2-one [CF3C(O)CHC(R)OMe, where R=Ph, 4-F-C6H4, 4-Br-C6H4, 4-I-C6H4, 4-CH3-C6H4, 4-CH3O-C6H4, Thien-2-yl, Biphen-4-yl] or β-enaminones [RC(O)CHCHNMe2, where R=Ph, 4-F-C6H4, 4-Br-C6H4, 4-I-C6H4, 4-CH3-C6H4, 4-CH3O-C6H4, 4-NO2-C6H4, Thien-2-yl, Biphen-4-yl, Naphth-2-yl, Pyrrol-2-yl, CCl3] with 5-amino-1,2,4-triazole in acetic acid at 99°C with 5-17min of ultrasound irradiation. This methodology has shown several advantages, such as shorter reaction times, mild conditions, high regioselectivity, and excellent yields, when compared with conventional thermal heating (oil bath).
 
Nanoparticles of a two-dimensional coordination polymer, {[Pb(L)(μ(1,1)-NCS)(H(2)O)]}(n) (1), (L(-)=1H-1,2,4-triazole-3-carboxylate), have been synthesized by a sonochemical process and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. The thermal stability of compound 1 both its bulk and nano-size has been studied by thermal gravimetric (TG) and differential thermal (DTA) analyses and compared each other. Concentration of initial reagents effects and the role of power ultrasound irradiation on size and morphology of nano-structured compound 1, have been studied. Calcination of the single crystals and nano-sized compound 1 at 400 °C under air atmosphere yields mixture of PbS and Pb(2)(SO(4))O nanoparticles. Results show that the size and morphology of the PbS and Pb(2)(SO(4))O nanoparticles are dependent upon the particles size of compound 1. A decrease in the particles size of compound 1 leads to a decrease in the particles size of the PbS and Pb(2)(SO(4))O.
 
An aqueous mediated novel synthesis of substituted 2'amino-4'benzoyl-2'-methyl spiro[indole 3,5'-[1,3]oxathiolane]-2(1H)-ones (2a-f) was carried out from the reaction of spiro [indole-3,2'-oxiranes] (1a-f) with thioacetamide in the presence of LiBr as catalyst. The reaction was carried out under both microwaves and sonication and results were also compared with conventional method. In general, improvement in rate and yields observed when reaction was carried out under sonication as compared to microwave irradiation and conventional method.
 
Montmorillonite K-10 and KSF were found to be highly efficient, environmentally friendly and recyclable heterogeneous catalysts for the selective synthesis of a variety of 2-aryl-5,6-dihydro-4H-1,3-oxazines from arylnitriles and 3-amino-1-propanol under ultrasound irradiation. This new methodology provides excellent yields in short reaction times (10-25 min). The reaction work-up is very simple and the catalysts can be easily separated from the reaction mixture and reused several times in subsequent reactions. This catalytic system also exhibits excellent chemoselectivity in the synthesis of mono-oxazines from dinitriles.
 
A facile and efficient one-pot three-component procedure for synthesis of novel dispirooxindolecyclo[pyrrolo[1,2-c]thiazole-6,5'-thiazolidine] derivatives without any catalysts under ultrasonic condition has been developed. Combining with the advantages of sonochemistry, such as mild reaction conditions, good yield and short reaction times, we have made a progress on construction of novel disiproheterocyclic compounds via the 1,3-dipolar cycloaddition of azomethine ylides. Several experiments were especially carried out for investigating the acceleration mechanism of ultrasound on the cycloaddition.
 
A convenient and efficient one-pot synthesis of 2,3-epoxyl-1,3-diaryl-1-propanone directly from acetophenones and aromatic aldehydes under ultrasound irradiation at room temperature has been described. In comparison to two-step methods, the present procedure has the advantages of mild conditions, shorter reaction time, without isolation of any intermediate, saves energy and no requirement of toxic solvent.
 
The effects of sonochemical treatment of a NaK eutectic mixture as catalyst on the side-chain alkenylation of o-xylene with 1,3-butadiene were studied. The parameters studied include ultrasound frequency, insonation time, sonication power as well as the reaction temperature. In addition, the effect of N,N,N',N'-tetramethylethylenediamine (TMEDA) on the reaction was also studied. The results showed that sonochemical treatment of this NaK eutectic mixture catalyst resulted in excellent conversion (up to 83.16%) under mild conditions. The introduction of TMEDA further increased the conversion to 89.4%.
 
Model reaction, conditions, and yield. a
Synthesis of oxindoles 3.
A simple and efficient procedure for the synthesis of 2,2'-(2-oxoindoline-3,3-diyl)bis(1H-indene-1,3(2H)-dione) derivatives, 2,2'-(2-oxo-1,2-dihydroacenaphthylene-1,1-diyl)bis(1H-indene-1,3(2H)-dione) and 2,2'-(1,3-dioxo-2,3-dihydro-1H-indene-2,2-diyl)bis(1H-indene-1,3(2H)-dione) by the reaction of 1,3-indandione and isatins or acenaphthylene-1,2-dione or ninhydrine in ethanol under ultrasonic irradiation in the presence of p-TSA is reported. The advantages of this method are the use of an inexpensive and readily available catalyst, easy work-up, good yields, and the use of ethanol as a solvent that is considered to be relatively environmentally benign.
 
A convenient one-pot protocol was developed for the synthesis of 2-imino-1,3-thiazolidin-4-ones by the reaction of amines, isocyanates, aldehydes, and chloroform in the presence of sodium hydroxide under ultrasonic conditions in high yields (75-91%) and shorter reaction times (12-15 min).
 
The synthesis of 5-aryl-1,3-diphenylpyrazole via the reactions of 3-aryl-2,3-epoxy-1-phenyl-1-propanone with phenylhydrazine was carried out in 69-99% yields at room temperature under ultrasound irradiation. This method provides several advantages such as operational simplicity, higher yield and environment friendly.
 
In the present work, kinetics of synthesis of 1,3-bis(allyloxy)benzene was successfully carried out by O-allylation of resorcinol with allyl bromide using aqueous potassium hydroxide and catalyzed by a new multi-site phase-transfer catalyst viz., 1,3,5,7-tetrabenzylhexamethylenetetraammonium tetrachloride, MPTC under ultrasonic (40kHz, 300W) assisted organic solvent condition. The pseudo first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (40kHz, 300W) in a batch reactor, it shows that the overall reaction rate can be greatly enhanced to seven fold faster with ultrasound irradiation than without ultrasound. The present study provides a method to synthesize ethers by ultrasound assisted liquid-liquid phase-transfer catalysis condition.
 
This paper presents a novel solvent free method of synthesis of trans-chalcones. The method was based on ultrasound irradiation of the reagents (aryl methyl ketones and aryl aldehydes) in presence of commercial acid-montmorillonites as catalysts. The trans-chalcones were synthesized in high yields (85-95%) and excellent selectivity in a short reaction time.
 
A task-specific ionic liquid (TSIL) has been introduced as a recyclable catalyst in Michael addition. A series of nitroalkenes and various C-based nucleophiles were reacted in the presence of 30mol% of recyclable basic-functionalized ionic liquid. Good to excellent yields were obtained in 30min under ultrasound irradiation.
 
Plot of the apparent rate constant versus various stirring speeds; propargylation of indene-1,3-dione under ultrasonic condition: 30 g of KOH, 40 mL of H 2 O, 0.0331 mol of propargyl bromide, 0.2 g of internal standard (biphenyl), 0.5 g of PTC, 30 mL of chlorobenzene, 45 °C; ultrasound conditions (40 kHz, 300 W).
Effect of the amount of PTC on the apparent rate constant: propargylation of indene-1,3-dione under ultrasonic condition: 30 g of KOH, 40 mL of H 2 O, 0.0331 mol of propargyl bromide, 0.2 g of internal standard (biphenyl), 30 mL of chlorobenzene, 600 rpm, 45 °C; ultrasound conditions (40 kHz, 300 W).
Arrhenius plot; propargylation of indene-1,3-dione under ultrasonic condition: 30 g of KOH, 40 mL of H 2 O, 0.0331 mol of propargyl bromide, 0.2 g of internal standard (biphenyl), 0.5 g of PTC, 30 mL of chlorobenzene, 600 rpm, ultrasound conditions (40 kHz, 300 W).
Effect of ultrasonic frequency.
Effect of organic solvents.
In the present study, kinetics of synthesis of 2,2-di(prop-2-ynyl)-1H-indene-1,3(2H)-dione was successfully carried out by propargylation of indene-1,3-dione with propargyl bromide using aqueous potassium hydroxide and catalyzed by a newly synthesized phase-transfer catalyst viz., N-benzyl-N-ethyl-N-isopropylpropan-2-ammonium bromide, PTC under ultrasonic (40kHz, 300W) assisted organic solvent condition. The pseudo first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (40kHz, 300W) in a batch reactor, it shows that the overall reaction rate can be greatly enhanced with ultrasound irradiation than without ultrasound.
 
The removal of nitroaromatics from polluted water is difficult due to their high stability to conventional treatment methods. This paper presents a method for the destruction of 1,3-dinitrobenzene and 2,4-dinitrotoluene in aqueous solutions. The compounds are shown to be stable to reaction with ozone, even under ultrasonic activation. The use of ultrasound enhances the rate of electrochemical reduction but the overall rate of reaction is still slow. However, the simultaneous application of ultrasound and ozonation to the electrochemical reaction allows virtually complete destruction of the compounds in short times. The effect is attributed to the ultrasonic enhancement of the electrochemical process giving intermediates that are susceptible to ozone oxidation. While further analytical work is needed to deduce the exact contributions of the various possible degradation mechanisms, the work demonstrates the synergies that can be gained by using combined techniques for the destruction of these difficult compounds.
 
Synthesis of 2,3-epoxyl-1,3-diaryl-1-propanone via epoxidation of chalcone with aqueous sodium hypochlorite was carried out in 62-92% yields using benzyldimethyltetradecyl ammonium chloride as phase transfer catalyst under ultrasound irradiation. Compared to the classical method, the advantages of this method are a safer oxidant, mild conditions, no toxic solvent and shorter reaction time.
 
Production of structured lipid 1,3-dioleoyl-2-palmitoylglycerol (OPO), from tripalmitin (PPP) and oleic acid (OA) using lipases and ultrasonic pretreatment was conducted. Factors influencing both the ultrasonic conditions and enzymatic reaction were investigated. Optimum conditions could be attained with 6min pretreatment time, 50% ultrasonic power, 3s/9s (work/pause) cycle of ultrasonic pulse, 1:8 PPP/OA molar ratio, 12% enzyme dosage and 50°C temperature of. At the optimum conditions, the OPO yield of 51.8% could be achieved in 4h. Studies showed that the OPO content increased to 35.9% in 1h with ultrasonic pretreatment, in comparison to 4h without ultrasonic pretreatment. Reuse of Lipozyme RM IM for 10 cycles under ultrasonic irradiation did not cause essential damage to its lipase activity. Reaction kinetic model fitted well with the proposed Ping-Pong mechanism. The apparent kinetic constant (Vm'/K2) of ultrasound pretreatment reaction was 2.52 times higher than the conventional mechanical stirring, indicating that ultrasound pretreatment enhanced the substrates affinity to the enzyme. This study confirmed that ultrasonic pretreatment was more efficient in OPO production than conventional mechanical agitation. Copyright © 2014 Elsevier B.V. All rights reserved.
 
Novel substituted 1,3,4-thiadiazole and bi(1,3,4-thiadiazole) were synthesized from reaction of 1-methyl-5-oxo-3-phenyl-2-pyrazolin-4-thiocarbox-anilide with a series of different hydrazonyl halides or N,N'-diphenyl-oxalodihydrazonoyl dichloride. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with classical condition. Structures of the products were established on analytical and spectral data.
 
Two-component synthesis of 2-aryl-1,3,4-oxadiazoles derivatives 5a-n (see Table 3 and text).
Synthesis of 2-phenyl-1,3,4-oxadiazole (5a) in different solvent systems under ultrasonic irradiation at room temperature.
Ultrasound promoted synthesis of 2-aryl-1,3,4-oxadiazoles at ambient temperature is reported. The remarkable features of the new procedure are shorter reaction time, excellent yields, cleaner reaction profile and simple experimental and workup procedure.
 
Synthesis of 2-aroyl-1,3,5-triaryl-4-carbethoxy-4-cyanocyclohexanols from chalcones with ethyl cyanoacetate is carried out in excellent yields with KF/basic alumina as catalyst under ultrasound irradiation.
 
The combination of ultrasound and photochemistry has been used for the oxidation of unsymmetrical 1,4-dihydropyridines to the pyridine derivatives. An ultrasonic probe of 24 kHz frequency and a Hg-lamp of 100 W have been used for this study. The effect of parameters such as ultrasonic intensity, the presence of oxygen and argon atmospheres and also the separate usage of one of these irradiation sources have been studied. Whereas sonication of these compounds alone did not result in the oxidation of them, the use of ultrasound increases the rate of photo-oxidation. The presence of oxygen decreases or increases the rate of reaction, depending on the type of excited state of 1,4-dihydropyridines involved in the reaction.
 
Scheme 1. Synthesis of 2-(1,5-diaryl-1,4-pentadien-3-ylidene)-hydrazinecarboximidamide hydrochloride.
Amidinohydrazone compounds are very important synthetic intermediates and can serve as versatile precursors in synthesis of many natural products and drug molecules. The use of ultrasound, p-dodecylbenzenesulfonic acid (DBSA) and water as solvent improved the synthesis of different 2-(1,5-diaryl-1,4-pentadien-3-ylidene)-hydrazinecarboximidamide hydrochlorides. The best reaction conditions for the condensation of 1,5-diphenyl-1,4-pentadien-3-one with aminoguanidine hydrochloride were as follows: 1,5-diphenyl-1,4-pentadiene-3-one (1, 1 mmol), aminoguanidine hydrochloride (1.1 mmol), DBSA (0.5 mmol), water 10 mL, reaction temperature 25-27°C, irradiation frequency 25 kHz. 2a was achieved in 94% yield within 2h. The other seven amidinohydrazones were obtained in 84-94% yield within 2-3h under the same conditions. Compared to the method involving catalysis by hydrochloric acid in refluxing EtOH, the advantages of present procedure are milder conditions, shorter reaction times, higher yields, and environmental friendly conditions, which make it a useful strategy for the synthesis of analogues.
 
The yields of 1,4-diazabutadienes under ultrasonic irradiation.
An ultrasound-assisted preparation of 1,4-diazabutadienes via smooth condensation of diketones with amines under solvent-free conditions is described. The generality of this method was examined by the synthesized N,N'-diaryl- and N,N'-dialkyl-1,4-diazabutadiene derivatives. In addition to experimental simplicity, the main advantages of the procedure are mild conditions, short reaction time (2-15 min) and high yields (71-98%).
 
The mass spectra of sonolytic products of ACTH18-39 (Mr. 2465.7) with 1,4-benzenedithiol addition and ultrasound irradiation for (a) 18 min and (b) 60 min. All noted peaks indicate sonolytic products. Asterisk indicates peaks originating from the matrix.
The change in signal-to-noise ratio (S/N) of a product ion peak at m/z 761 originated from the hydrolysis at peptide bond between tyrosine (Y6) and proline (P7) of ACTH18-39.
The mass spectrum of sonolytic products of glucagon (Mr. 3282.8) with added 1,4-BDT and 15 min ultrasound irradiation. All noted peaks indicate sonolytic hydrolysis fragments of glucagon. Asterisk represents peaks originating from the matrix.
Amino acid sequence and corresponding m/z values of protonated hydrolytic products of ACTH18-39 and glucagon.
Described here is the sonolytic hydrolysis of peptides achieved by treatment of aqueous solution to which the radical scavenger 1,4-benzenedithiol (1,4-BDT), which has hydrogen donating ability, has been added. Mass spectrometric analysis of the products of sonolytic hydrolysis gave information about amino acid sequence of the peptides without any byproducts. The additive 1,4-BDT improves the sonolytic hydrolysis of peptides in terms of the rate of hydrolysis reaction and the amount of additive required when compared to catechol, a previously reported additive. The sonolytic hydrolysis of peptides differs from both acid hydrolysis and hydrogen atom-induced dissociation named matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD), in characteristics. We propose a mechanistic reaction for the sonolytic hydrolysis of peptides, based on the mechanisms of both acid hydrolysis and MALDI-ISD processes. The sonolytic hydrolysis of peptides upon addition of hydrogen donating radical scavengers can be rationalized via the attachment of a hydrogen atom to the carbonyl oxygen with subsequent hydrolysis.
 
The condensation of aldehydes, ethyl acetoacetate and ammonium acetate result 1,4-dihydropyridines in 82-99% yields under ultrasound irradiation without solvent and catalyst at room temperature. Compared with conventional methods, the main advantages of the present procedure are milder conditions, shorter reaction time and higher yields.
 
1,5-Dinitroaryl-1,4-pentadien-3-ones were synthesized with ultrasound irradiation in the presence of K(2)CO(3) as catalyst. The reaction mechanism and the factors influencing the product were also discussed. The present procedure is more convenient with shorter reaction time and higher yields compared with conventional methods.
 
Irradiation of ultrasound accelerated the rate of the photochemical disappearance of 4,4'-dihalogenated benzils in 1,4-dioxane in the order of halogen = I, Br > Cl > F. 4,4'-dimethoxy and unsubstituted benzils did not show acceleration. Possible mechanisms of the acceleration are discussed.
 
Schematic illustration of sonoluminescence measurement.  
Effect of SiO 2 or TiO 2 addition on the destruction of 1,4-dioxane in aqueous systems.  
Sonoluminescence by sonication.  
Temperature change of water or suspension during sonolysis.  
Effect of reduced TiO 2 addition on the destruction of 1,4-dioxane in water.  
Effects of TiO(2) powder addition on sonochemical destruction of 1,4-dioxane in water were investigated through comparison of a SiO(2) powder that had similar specific surface area. Results show that addition of TiO(2) is more effective for decomposition of 1,4-dioxane in water than addition of SiO(2). The contribution of photocatalytic destruction through sonoluminescence is not a dominant mechanism for acceleration of sonochemical reactions by adding TiO(2). Sonication of TiO(2)-added water generated thermally excited holes in this case. Moreover, intrinsic oxygen vacancies in TiO(2) surface play an important role in achieving high decomposition efficiency by producing cavitation. The addition of reduced TiO(2) powder increases both the ultrasonication energy that is consumed in water and the destruction efficiency of 1,4-dioxane.
 
Top-cited authors
Timothy James Mason
  • Coventry University
Aniruddha Bhalchandra Pandit
  • Institute of Chemical Technology, Mumbai
Parag R Gogate
  • Institute of Chemical Technology, Mumbai
Mircea Vinatoru
  • Polytechnic University of Bucharest
Christian Pétrier
  • Sonochemistry network