Ultrasound promoted regioselective nitration of phenols using dilute nitric acid in the presence of phase transfer catalyst

Phenols are selectively nitrated to o-nitrophenol along with rate enhancement using dilute nitric acid (6 wt%)/tetra butyl ammonium bromide (TBAB) under sonication. The selectivity can also be reversed to p-nitrophenol using NaBr as a catalyst. Kinetic analysis of nitration of phenol both with and without sonication has been investigated by variation of reaction parameters such as catalyst, nitric acid and substrate concentration.     

Ultrasonically promoted nitrolysis of DAPT to HMX in ionic liquid

The present work aims at developing a new process to synthesize HMX from DAPT using ultrasound in ionic liquid. Reaction has been carried out in ultrasonic bath, effect of various parameters such as presence and absence of ultrasound, volume and type of solvent, temperature, concentration of nitrating agent has been investigated with an aim of obtaining the optimum conditions for the synthesis of HMX. It was observed that ultrasonically promoted nitroylsis of DAPT to HMX has exhibited significant enhancement in yield at ambient condition.     

Ultrasound promoted synthesis of Nile Blue derivatives

Ultrasound irradiation was used for the first time towards the synthesis of new Nile Blue related benzo[a]phenoxazinium chlorides possessing isopentylamino, (2-cyclohexylethyl)amino and phenethylamino groups at 5-position of the heterocyclic system. The efficacy of sonochemistry was investigated with some of our earlier reported synthesis of benzo[a]phenoxazinium chlorides. This newer protocol proved competent in terms of reaction times and enhanced yields. Photophysical studies carried out in ethanol, water and simulated physiological conditions, revealed that emission maxima occurred in the range 644–656 nm, with high fluorescent quantum yields. Other attractive feature exhibited by these materials includes good thermal stability. These properties might be useful in the development of fluorescent probes for biotechnology.     

Ultrasound promoted synthesis of some novel fused pyrans

Novel fused pyrans were synthesized from the reaction of the tetrahydropyran-4-one with arylidine malononitriles. Different fused pyran derivatives were obtained from the mentioned reaction depending on type of catalyst used and type of energy used. Reactions were carried out under silent and ultrasonic conditions. In general, it was found that sometimes ultrasound irradiations change the reaction path in comparing with silent condition. In addition to improvement in reaction times, the products were obtained in high yields and their structures were determined by elemental analyses, spectral data.     

Ultrasound and ionic liquid: an efficient combination to tune the mechanism of alkenes epoxidation

In this proof of concept study, the advantageous properties of both H₂O₂/NaHCO₃/imidazole/Mn(TPP)OAc oxidation system and MOPyrroNTf₂ ionic liquid have been combined under ultrasonic irradiation to give an exceptionally favorable environment for Mn(TPP)OAc catalyzed olefin oxidations. The results reveal the crucial role played by the ultrasonic irradiations that influence drastically the oxidation process. In MOPyrroNTf₂ and under ultrasonic irradiation, the mechanism probably involves an oxo-manganyl intermediate at the expense of the classical bicarbonate-activated peroxide route.     

Ultrasound promoted facile synthesis of arylhydrazones at ambient conditions

Arylhydrazones have been synthesized in excellent yields in short reaction times at ambient temperature conditions in the absence of any added catalyst by the reaction of phenylhydrazines with carbonyl compounds under ultrasonic irradiation.     

Ultrasound promoted Wurtz coupling of alkyl bromides and dibromides

Sonochemically enhanced Wurtz coupling using lithium metal has been investigated for a number of isomeric alkyl bromides under a variety conditions. The products result from direct coupling of short lived radicals formed at the metal surface rather than the secondary radicals which can be formed during coupling of aromatic halides and thus give rise to a single major product. Coupling has been extended to dibrominated aryl and alkyl compounds as well as showing that aryl-alkyl coupling is possible. Dibrominated alkyls were found to give low molecular weight oligomers although no reaction occurred for 1,2-isomers. The growth of oligomers in THF may be solubility limited. A simple model is proposed to explain these findings.     

Ultrasound absorption in liquid metals

The excess longitudinal ultrasonic absorption over and above the classical value has been attributed to the solid-like mechanisms of the interaction of sound waves with the conduction electrons and the thermal phonons in liquid metals, both exhibiting a quadratic dependence on the sound frequency.     

Ultrasound promoted regioselective synthesis of beta-iodoethers from olefin-I2-alcohol

Regioselective synthesis of β-iodoethers in high yields by sonicating alkene and alcohol in the presence of iodine in a bath at 35 kHz is reported.     

An efficient synthesis of 1,8-dioxo-octahydro-xanthene derivatives promoted by a room temperature ionic liquid at ambient conditions under ultrasound irradiation

The condensation reaction involving an aldehyde and diketone was efficiently promoted by the Ionic liquid, [Hbim]BF(4) (IL) as a reaction medium with methanol as co-solvent at ambient temperature under ultrasonic irradiation to afford the corresponding 1,8-dioxo-octahydro-xanthene (xanthene) derivatives in excellent yields. The advantages of this method include among others the use of a recyclable, non-volatile ionic liquid, which promotes this protocol under ambient temperature without the requirement of any added catalyst. The reaction times and yields are compared with p-TSA catalyzed synthesis of xanthenes under thermal conditions, which is also reported for the first time under our reaction conditions.     

An efficient and facile nitration of phenols with nitric acid/zinc chloride under ultrasonic conditions

An efficient and facile nitration of phenols using nitric acid/zinc chloride under ultrasonic condition has exhibited significant chemo as well as regioselectivity. This study has been extended to other aromatic compounds like naphthalene and anthracene.     

Ultrasound promoted C-alkylation of benzyl cyanide--effect of reactor and ultrasound parameters

Phase transfer catalysis is used widely in the synthesis of various organic chemicals in both liquid-liquid and solid-liquid systems. The C-alkylation of benzyl cyanide by 2-bromopropane in the presence of sodium hydroxide was investigated. The reaction rate of the phase transfer reaction can be increased by ultrasound, but frequency and power of ultrasound and the geometry of the ultrasonic field inside the reactor influence the reaction strongly. The results demonstrate clearly, that to achieve a high efficiency of ultrasonic systems in chemical processes the ultrasonic parameters and geometry of the sonotrode had to be adopted.     

Ultrasound promoted synthesis of substituted pyrazoles and isoxazoles containing sulphone moiety

Novel pyrazoles and isoxazoles were synthesized from the reaction of the carbanions of 1-aryl-2-(phenylsulphonyl)-ethanone with different hydrazonyl halides and 1-aryl-2-bromo-2-hydroximinoethanone in ethanol, respectively. Reactions were carried out under silent and ultrasonic conditions. In general, it was found that ultrasound irradiations enable some reactions to occur which could not be carried out under silent condition in addition to improvement in reaction times. The products were obtained in high yields and their structures were determined by elemental analyses, spectral data and X-ray diffraction.     

Surface nanocrystallization of an ionic liquid

Surface crystallization at the vapor-liquid interface of the ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) is observed in synchrotron x-ray diffraction studies. Sharp Bragg reflections emerge in grazing-angle x-ray diffraction patterns 37?°C above the bulk melting temperature, indicating the presence of a long-range ordered phase at the surface in coexistence with the bulk parent liquid. The unique structure of the vapor-liquid interface where butyl chains attached to the cations are expelled to the vapor side facilitates interionic electrostatic interactions that lead to the crystallization. Our results demonstrate the complexity of ionic-liquid structure with their tendency to spontaneously phase separate into nanodomains with finite correlation lengths in coexistence with the liquid phase. By virtue of interfacial boundary conditions, these nanodomains grow laterally to form quasi-two-dimensional crystals.     

Ultrasound promoted N-alkylation of pyrrole using potassium superoxide as base in crown ether

Ultrasound accelerates the N-alkylation of pyrrole by alkylating reagents using potassium superoxide as base in the presence of 18-crown-6. A much lower yield of N-alkylated pyrrole was realized in the absence of ultrasound. N-alkylating reagents employed for pyrrole are methyl iodide, ethyl bromide, benzyl bromide, as well as acrylonitrile allyl cyanide and methyl acrylate. In an extension of this work, we have found that ultrasound was not necessary for the N-alkylation of indole and alkyl amine, such as diphenyl amine and piperidine with alkyl halides using our reagents. In all cases we observed that the 18-crown-6 catalyzed N-alkylation reaction gives higher yields of N-alkylated products than that without crown ether, when potassium superoxide was used as base. These observations are probably due to the potassium-crown complex which can be released when the reaction goes to completion.     

Effect of ionic liquid on chain segment motion and charge detrapping in poly(l-lactide)/ionic liquid composites

The effect of ionic liquid on the chain segment motion and charge detrapping in poly(l-lactide) (PLA)/ionic liquid (IL) composites has been investigated by means of thermally stimulated depolarization current (TSDC), scanning electron microscopy, and differential scanning calorimetry. There are four current peaks (namely, α, ρ₁, ρ₂, and ρ₃ peaks, respectively) in TSDC spectra of PLA and PLA/IL composites. The α peak corresponds to the glass transition, the ρ₁ peak is attributed to space charge trapped in the amorphous phase, the ρ₂ peak is originated from space charge trapped in the interphase that includes PLA/IL interface and crystalline/amorphous interface of PLA, and the ρ₃ peak is originated from space charge trapped in the crystalline phase. With the increase of IL content from 0 to 5phr, ρ₂ and ρ₃ peaks gradually merge into one single peak. By analyzing the characteristic parameters of these peaks, it is found that IL can accelerate the mobility of chain segments and increase structural defects in PLA/IL composites. In addition, IL decreases the stability of trapped charge in both amorphous and crystalline phases, but not affecting the stability of trapped charge in interphase.     

Ultrasound promoted clay catalyzed efficient and one pot synthesis of substituted oxindoles

A simple facile, one-pot synthesis of oxindoles in reasonable purity is reported via intramolecular Friedal-Craft cyclization. Clay KSF is an inexpensive, efficient and mild catalyst for the synthesis of substituted oxindoles by the reaction of chloroacetyl chloride and various anilines under the influence of ultrasonic irradiation under solvent-free conditions. The remarkable advantages of this method are the simple experimental procedures, short reaction times, high yields of products, suitability for a wide variety of substituents, and the green aspects through the avoidance of toxic catalyst and solvents.     

Ultrasound promoted synthesis of 2-aroyl-1,3,5-triaryl-4-carbethoxy-4-cyanocyclohexanols

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.     

Ultrasound promoted synthesis of thioesters from 2-mercaptobenzoxa(thia)zoles

An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields.