Efficient and selective hydrocarbon oxidation with sodium periodate under ultrasonic irradiation catalyzed by polystyrene-bound Mn (TPyP)

Rapid, efficient and selective alkene epoxidation and alkane hydroxylation with sodium periodate catalyzed by Mn (TPyP) supported on chloromethylated polystyrene, [Mn(TPyP)-CMP], under ultrasonic irradiation were reported. This catalytic system showed high selectivity in epoxidation of stilbenes and R-(+)-limonene and exhibits a particular ability to epoxidize linear alkenes such as 1-heptene. This supported catalyst can catalyze the oxidation of very inert saturated hydrocarbons as well as alkylbenzene derivatives with NaIO4 under ultrasonic irradiation. Under mild reaction conditions, this catalyst was consecutive reused five times without detectable catalyst leaching and gave over 95% epoxide yield in the epoxidation of styrene.     

Intensification of heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction using ultrasound: Understanding effect of operating parameters

Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction is a significant reaction for obtaining industrially important products. The current research work deals with intensification of reaction of 4-bromoanisole and phenylboronic acid catalyzed with 5 wt% Pd/C (5% by weight Pd supported on C available as commercial catalyst) using ultrasound and more importantly, without use of any additional phase transfer catalyst. Heterogeneous catalyst has been selected in the present work so as to harness the benefits of easy separation and the possible limitations of heterogeneous operation are minimized by introducing ultrasonic irradiations. The effect of operating parameters such as ultrasound power, temperature, catalyst loading and molar ratio on the progress of reaction has been investigated. It has been observed that an optimum power, temperature and catalyst loading exist for maximum benefits whereas higher molar ratio was found to be favourable for the progress of the reaction. Also, the use of ultrasound reduced the reaction time from 70 min required in conventional approach to only 35 min under conditions of frequency of 22 kHz, power dissipation of 40 W and catalyst loading as 1.5 mol% (refers to total quantum of catalyst used in the work) in ethanol-water system under ambient conditions. The work also demonstrated successful results at ten times higher volume as compared to the normally used volumes in the case of simple ultrasonic horn. Overall, the work has successfully demonstrated process intensification benefits obtained due to the use of ultrasound for heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction.     

The application of poly(N, N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) and N, N, N′, N′-tetrabromobenzene-1,3-disulfonamide as catalysts for one-pot synthesis of 2-aryl-1-arylmethyl-1H-1,3-benzimidazoles and 1,5-benzodiazepines, and new reagents for synthesis of benzimidazoles

A new, facile, and efficient procedure for conjugate addition of indole and pyrrole with Michael acceptors have been developed for pulverization–activation reaction catalyzed by wet cyanuric chloride (2,4,6-trichloro-[1,3,5]-triazine or TCT) through grinding under solvent-free conditions at room temperature. Also, double-conjugate 1,4-addition of indoles to dibenzylidenacetones and conjugate addition of thiols with Michael acceptors using wet-TCT as catalyst is reported.     

Rapid esterification of fatty acid using dicationic acidic ionic liquid catalyst via ultrasonic-assisted method

Biodiesel production via esterification/transesterification reactions can be catalyzed by homogenous or heterogeneous catalysts. Development of heterogeneous catalysts for biodiesel production is highly advantageous due to the ease of product purification and of catalyst recyclability. In this current work, a novel acidic [DABCODBS][CF₃SO₃]₂ dicationic ionic liquid (DIL) was used as heterogeneous catalyst to produce biodiesel using oleic acid as model oil. The esterification was conducted under ultrasonic irradiation (20 kHz) using a 14 mm ultrasonic horn transducer operated at various duty cycles. It was observed that the duty cycle, amplitude, methanol to oil molar ratio, catalyst amount and reaction temperature were the major factors that greatly impact the necessary reaction time to lead to a high yield of biodiesel. The reaction conditions were optimized with the aid of Response Surface Methodology (RSM) designed according to the Quadratic model of the Box Behnken method. The optimum conditions were found to be at catalyst amount of 0.64 mol%, methanol to oil ratio of 14.3:1, temperature of 59 °C, reaction time of 83 min and amplitude of 60% in continuous mode. The results showed that the oleic acid was successfully converted into esters with conversion value of 93.20% together with significant reduction of reaction time from 7 h (using mechanical stirring) to 83 min (using ultrasonication). The results also showed that the acidic DIL catalyst we designed purposely was efficient to catalyze the ultrasonic-assisted esterification yielding high conversion of oleic acid to methyl oleate on short times. The DIL was also recycled and reused for at least five times without significant reduction in performance. Overall, the procedure offers advantages including short reaction time, good yield, operational simplicity and environmentally benign characteristics.     

Ultrasound assisted enzyme catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate

The present work illustrates the transesterification of glycerol to glycerol carbonate (GlyC) from dimethyl carbonate (DMC) using commercial immobilized lipase (Novozym 435) under ultrasonic irradiation. The experiments were performed in a batch reactor placed in an ultrasonic water bath using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound power on the conversion of glycerol to GlyC. It has been found that ultrasound-assisted lipase-catalyzed transesterification of glycerol would be a potential alternative to conventional alkali-catalyzed method, as high conversion (99.75%) was obtained at mild operating conditions: molar ratio of DMC to glycerol 3:1, catalyst amount of 13% (w/w), lower power input (100 W), duty cycle 50% and temperature (60 °C) in a relatively short reaction time (4 h) using Novozym 435 as catalyst. Ultrasound reduces the reaction time up to 4 h as compared to conventional stirring method (14 h) catalyzed by Novozym 435. The repeated use of the catalyst under the optimum experimental condition resulted in decay in both enzyme activity and product conversion.     

Simultaneous sonication assistance for the synthesis of tetrahydropyridines and its efficient catalyst ZrP2O7 nanoparticles

In this research, a general synthetic method for the synthesis of tetrahydropyridines were developed using ZrP₂O₇ nanoparticles under ultrasonic irradiations. Firstly by a simple and green process, nano zirconium pyrophosphate was prepared via sonication. Subsequently, this nanoparticle was used as an efficient catalyst for the synthesis of highly functionalized tetrahydropyridines via five-component reaction of aromatic aldehyde, amine and ethyl acetoacetate in ethanol under ultrasound irradiation. The present approach offers several advantages such as high yields, environmentally benign, simple work-up, excellent yield of products, short reaction times as well as recoverability and reusability of the catalyst.     

VCl3 catalyzed imine-based multicomponent reactions for the facile access of functionalized tetrahydropyridines and β-amino carbonyls

Abstract  

A simple, mild, and highly efficient method has been developed for the preparation of functionalized tetrahydropyridines and β-amino carbonyls from the multicomponent reactions involving in situ imines and vanadium (III) chloride as a Lewis acid. The multicomponent reaction of two equivalents of aromatic aldehyde, two equivalents of amine, and one equivalent β-keto ester in the presence of catalytic amount of VCl₃ provides highly atom economic five-component tetrahydropyridines in very good yields. The same catalyst was found useful for the efficient synthesis of a wide variety of β-amino ketones using direct-type Mannich reaction of aromatic aldehyde, amine, and aromatic ketones. The notable advantages of this method are simple procedure, short reaction time and good yields, and applicable to broad range of substrates.     

Rapid and efficient synthesis of 4(3H)-quinazolinones under ultra sonic irradiation using silica-supported Preyssler nano particles

A new synthesis of 4(3H)-quinazolinone from the reaction of 2-amino-benzamide, and acylchlorides in the presence of catalytic amounts of silica-supported Preyssler nano particles as green, reusable and efficient catalyst under ultra sonic irradiation is reported.     

Sono-photo-Fenton oxidation of bisphenol-A over a LaFeO3 perovskite catalyst

In this study, oxidation of bisphenol-A (IUPAC name – 2,2-(4,4-dihydroxyphenyl, BPA), which is an endocrine disrupting phenolic compound used in the polycarbonate plastic and epoxy resin industry, was investigated using sono-photo-Fenton process under visible light irradiation in the presence of an iron containing perovskite catalyst, LaFeO₃. The catalyst prepared by sol–gel method, calcined at 500 °C showed a catalytic activity in BPA oxidation using sono-photo-Fenton process with a degradation degree and a chemical oxygen demand (COD) reduction of 21.8% and 11.2%, respectively. Degradation of BPA was studied by using individual and combined advanced oxidation techniques including sonication, heterogeneous Fenton reaction and photo oxidation over this catalyst to understand the effect of each process on degradation of BPA. It was seen, the role of sonication was very important in hybrid sono-photo-Fenton process due to the pyrolysis and sonoluminescence effects caused by ultrasonic irradiation. The prepared LaFeO₃ perovskite catalyst was a good sonocatalyst rather than a photocatalyst. Sonication was not only the effective process to degrade BPA but also it was the cost effective process in terms of energy consumption. The studies show that the energy consumption is lower in the sono-Fenton process than those in the photo-Fenton and sono-photo- Fenton processes.     

Sonication effect on the reaction of 4-bromo-1-methylbenzene with sodium sulfide in liquid–liquid multi-site phase-transfer catalysis condition – Kinetic study

The synthesis of di-p-tolylsulfane from the reaction of 4-bromo-1-methylbenzene (BMB) with sodium sulfide was carried out using a multi-site phase-transfer catalyst (MPTC) viz., 1,4-dihexyl-1,4-diazoniabicyclo[2.2.2]octanium dibromide and ultrasonic irradiation in a liquid–liquid reaction condition. The overall reaction rate is greatly enhanced when catalyzed by multi-site phase-transfer catalyst (MPTC) combined with sonication (40 kHz, 300 W) in a batch reactor than catalyzed by MPTC without sonication. Effects on the reaction due to various operating conditions, such as agitation speed, different ultrasound frequencies, different phase-transfer catalysts, different organic solvents, the amount of MPTC, temperature, amount of sodium sulfide, effect of sodium hydroxide, volume of n-hexane and the concentration of 4-bromo-1-methylbenzene. The reaction obeys a pseudo first-order rate law and a suitable mechanism was proposed based on the experimental observation.     

Mechanistic insights into N‐heterocyclic carbene (NHC)‐catalyzed N‐acylation of N‐sulfonylcarboxamides with aldehydes

In the current work, density functional theory calculations were performed to elucidate the detailed reaction mechanism for N‐heterocyclic carbene (NHC)‐catalyzed oxidative N‐acylation reaction of amides with aldehydes affording imide products. According to the calculated results, the reaction is initiated by the nucleophilic attack of NHC to aldehydes forming zwitterionic intermediate, which can then form Breslow intermediate via proton transfer. The Breslow intermediate can then be oxidized affording the oxidative intermediate, which can then go through 1,2‐addition with the deprotonated N‐sulfonylcarboxamides. Subsequently, elimination of NHC catalyst produces the final imide product. Our results reveal that the proton in N‐sulfonylcarboxamides is probably abstracted by base t‐BuOK or DPQH, and the deprotonation process is barrier‐less. Moreover, for the second step, ie, the formation of Breslow intermediate, direct proton transfer is impossible to occur. On the contrary, the results reveal that t‐BuOH can mediate the proton transfer in this step and significantly lower the energy barrier to 24.1 kcal/mol, which is also the highest energy barrier for the whole reaction. The work provides not only valuable clues for elucidating the detailed reaction mechanism for the invaluable NHC‐catalyzed oxidative reactions but also mechanistic insights for the rational design of novel NHC‐catalyzed oxidative reactions in the future.     

Ultrasonically-promoted synthesis of mandelic acid by phase transfer catalysis in an ionic liquid

An efficient and facile process to synthesize mandelic acid through phase transfer catalysis (PTC; also phase transfer catalyst) using ultrasound in an ionic liquid has been developed. Mandelic acid was synthesized from benzaldehyde with chloroform in an 89.6% yield at 60°C for 2h by using tetrabutyl ammonium bromide (TBAB) as a phase transfer catalyst. Effects of different factors, such as frequency of ultrasound, reaction temperature, kinds of PTC and solvents had been investigated to obtain the optimum condition. It was observed that the ultrasonically promoted synthesis of mandelic acid by PTC in the ionic liquid exhibited significant enhancement in reaction yields under ambient conditions.     

An efficient Bi(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> · 5H<Subscript>2</Subscript>O catalyzed multi component one-pot synthesis of novel Naphthyridines

An efficient and environmentally friendly multicomponent synthesis of substituted 1,8-naphthyridines catalyzed by bismuth(III) nitrate pentahydrate [Bi(NO(3))(3) . 5H(2)O] under solvent-free microwave irradiation is described. This procedure has such advantages as short reaction time, high yields, and simple workup. The catalyst could be reused several times, keeping its initial activity recycled reactions.     

A suitable preparation of <Emphasis Type="Italic">N</Emphasis>-sulfonyl-1,2,3,4-tetrahydroisoquinolines and their ring homologs with a reusable Preyssler heteropolyacid as catalyst

The preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines, N-sulfonyl-2,3,4,5-tetrahydro-1H-2-benzazepines and N-sulfonyl-1,2,3,4,5,6-hexahydrobenzazocine was catalyzed by a Preyssler heteropolyacid, H₁₄[NaP₅W₃₀O₁₁₀], (PA), supported on silica (PASiO₂40) with excellent yields by means of the Pictet–Spengler reaction of N-aralkylsulfonamides with s-trioxane. The reactions proceed with 0.5 mol% of silica-supported catalyst in toluene at 70°C. The catalyst can be recycled without appreciable loss of the catalytic activity.     

Ultrasound-assisted one-pot, three-component synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones

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.     

DFT studies on the mechanism of Pd(II)‐catalyzed intermolecular 1,2‐diamination of conjugated dienes

The reaction mechanism of the palladium(II)‐catalyzed addition of urea to dienes to form 1,2‐diamine was studied using the B3LYP density functional theory (DFT) method. The results indicate that the first C? N σ‐bond formation is the rate‐determining step, and that the covalent bonds are formed favorably by the terminal carbon atoms of dienes and nitrogen atom. The Pd(NCMe)‐catalyst may significantly lower the energy barrier of the rate‐determining step from the nonligand Pd(II)‐catalyst counterpart. The results are in strong support of a recent experiment. Copyright © 2008 John Wiley & Sons, Ltd.     

Mössbauer spectroscopy and nuclear inelastic scattering studies on polynuclear oxo-bridged iron catalyst—first results

Polynuclear iron catalysts are interesting materials because of their novel properties. In the future they may help to replace high cost and hazardous heavy metal catalysts by efficient, non toxic and economic iron compounds. In this work, we present some preliminary results on a novel polynuclear oxo-bridged iron catalyst. The chemical environment of the metal species (Fe) was studied under Gif-type conditions (Fe catalyst/Zn/O₂ in pyridine/acetic acid) with cyclohexene as substrate. Such Gif-type catalysts are able to catalyse the selective oxidation of alkanes and alkenes. The characterization was done by Mössbauer spectroscopy and nuclear inelastic scattering. In order to identify the intermediate species during the reaction (selective oxidation using molecular O₂), a freeze-quench technique was used. This also helps to understand the kinetics of the chemical reaction.     

Zinc triflate: a highly efficient reusable catalyst in the synthesis of functionalized quinolines via Friedlander annulation

An environmentally friendly and highly efficient procedure for the preparation of quinolines and fused polycyclic quinolines has been developed by a simple Friedlander annulation reaction of 2-aminoaryl ketone with carbonyl compounds in presence of zinc triflate under microwave irradiation and solvent-free conditions. The reaction also proceeds effectively when In(OTf)₃ was used in lieu of Zn(OTf)₂ as the catalyst. The catalyst can be recovered after the reaction and reused efficiently in subsequent runs.     

One‐pot oxidation of aromatic and cyclic hydrocarbons using the Au (III) and Pd (II) catalyst under microwave irradiation

We report here in highly efficient one‐pot catalytic system which utilizes in situ generated sodium ferrate for the oxidation of aromatic and cyclic hydrocarbons in the presence of Au (III) and Pd (II) metal ions catalyst under ecofriendly green synthetic method. Results of these studies revealed that Au (III) catalytic system gave higher yield as compared with Pd (II) catalytic system because of the higher electrode potential of Au(III) than Pd(II). All compounds were characterized by infrared and NMR spectral analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

Ultrasound assisted intensification of biodiesel production using enzymatic interesterification

Ultrasound assisted intensification of synthesis of biodiesel from waste cooking oil using methyl acetate and immobilized lipase obtained from Thermomyces lanuginosus (Lipozyme TLIM) as a catalyst has been investigated in the present work. The reaction has also been investigated using the conventional approach based on stirring so as to establish the beneficial effects obtained due to the use of ultrasound. Effect of operating conditions such as reactant molar ratio (oil and methyl acetate), temperature and enzyme loading on the yield of biodiesel has been investigated. Optimum conditions for the conventional approach (without ultrasound) were established as reactant molar ratio of 1:12 (oil:methyl acetate), enzyme loading of 6% (w/v), temperature of 40 °C and reaction time of 24 h and under these conditions, 90.1% biodiesel yield was obtained. The optimum conditions for the ultrasound assisted approach were oil to methyl acetate molar ratio of 1:9, enzyme loading of 3% (w/v), and reaction time of 3 h and the biodiesel yield obtained under these conditions was 96.1%. Use of ultrasound resulted in significant reduction in the reaction time with higher yields and lower requirement of the enzyme loading. The obtained results have clearly established that ultrasound assisted interesterification was a fast and efficient approach for biodiesel production giving significant benefits, which can help in reducing the costs of production. Reusability studies for the enzyme were also performed but it was observed that reuse of the catalyst under the optimum experimental condition resulted in reduced enzyme activity and biodiesel yield.