Solvent-free Phase Transfer Catalysis Research Articles

A Conventional and Green Synthesis of 3,3`-([1,1`-biphenyl]-4,4`-diylbis(azanylylidene))bis(indolin-2-one) Derivatives, Potential Monomers for Schiff base Polymers, Using an Ionic Liquid Catalyst

A number of 3,3`-([1,1`-Biphenyl]-4,4`-diylbis(azanylylidene))bis(indolin-2-ones) were synthesized by the conventional method and by a green method involving solvent-free phase transfer catalysis. The catalyst used is a quaternary ammonium salt aliquat 336. Mechanisms of reaction are proposed for the both synthesis methods. The structures of the products were confirmed by spectroscopic measurements. Schiff base monomers are good candidates for obtaining new polymers.

Improvement and simplification of synthesis of 3-aryloxy-1,2-epoxypropanes using solvent-free conditions and microwave irradiations. Relation with medium effects and reaction mechanism

Some 3-aryloxy-1,2-epoxypropanes, interesting as potential synthons in β-adrenergic receptor antagonists preparation, were obtained in excellent yields (65–96% within 2–17 min) by microwave activation (monomode system) using solid–liquid solvent-free phase transfer catalysis (PTC). The best results for the O-alkylation of some phenols with epichlorohydrin were obtained using TBAB and NaOH/K 2CO 3 (1:4 mol/mol) as phase transfer catalyst and more acceptable basic system, respectively. These new procedure is compared with classical methods. Significant specific microwave effect (non-purely thermal) was evidenced in all cases. They were discussed in terms of reaction medium and mechanism, taking into account the variations in polarity of the systems.

Microwave-assisted organic synthesis: one hundred reaction procedures

1. Preface 2. Interaction of microwaves with different materials 3. Microwave effect vs. thermal effect 3.1. Thermal activation during microwave irradiation 3.2. Non-thermal activation during microwave irradiation 4. Microwave equipment 4.1. Microwave generators 4.2. Transmission lines (waveguides) 4.3. Microwave applicators (cavities) 4.4. Microwave reactors 4.5. Temperature monitoring 4.6. Reaction vessels and glassware 5. Techniques for conducting chemical reactions under microwave irradiation 6. Safety precautions on the application of microwaves in laboratory 7. Reactions under microwave conditions 7.1. Reactions in homogenous media 7.2. Reactions of reagents supported on mineral supports 7.3. Solid-liquid solvent-free phase transfer catalysis (PTC) reactions 7.4. Reactions of neat reagents 7.5. Polymerization reactions 8. Concluding remarks

Eco‐friendly methodologies for the synthesis of some aromatic esters, well‐known cosmetic ingredients

Solid-liquid solvent-free phase transfer catalysis (PTC) and acidic catalysis in dry media were applied, with noticeable improvement and simplification over classical procedures in a Green Chemistry context, to the synthesis of some aromatic esters useful as cosmetic ingredients: 3-methylbutyl 4-methoxycinnamate, 2-ethylhexyl 4-methoxycinnamate, 2-ethylhexyl 4-(dimethylamino)benzoate and 2-ethylhexyl salicylate, well-known ultraviolet B sunscreen filters; 4-isopropylbenzyl salicylate, UV absorber and cutaneous antilipoperoxidant; propyl 4-hydroxybenzoate and butyl 4-hydroxybenzoate (parabens), antimicrobial agents. The reactions were performed under microwave (MW) activation and conventional heating. The best results for the synthesis of cinnamic, salicylic and 4-(dimethylamino)benzoic esters were achieved by in situ preformed carboxylates alkylation with alkyl bromides using PTC. The 4-hydroxybenzoates were obtained in good yields by classical esterification of the acid with alcohols using a simple heterogeneous mixture of reagents with catalytic amounts of p-toluenesulfonic acid (PTSA). The comparisons of yields and thermal profiles under either MW or conventional heating were studied and reported.

Microwave‐Assisted Synthesis of Diaryl Ethers from Reactions of Phenols with Nitroaryl Fluorides under Solvent‐Free Conditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Selective and efficient fluorination of chlorodiazines under solvent-free phase transfer catalysis

3-Chloro-6-phenylpyridazine, 2,3-dichloroquinoxaline and 1,4-dichlorophthalazine were reacted with KF under solvent-free conditions in the presence of a phase transfer agent, with or without microwave irradiation. The chlorine–fluorine exchanges were obtained with enhanced yields and selectivities when compared with previous methods.

Microwave-assisted Synthesis of Diaryl Ethers from Reactions of Phenols with Nitroaryl Fluorides under Solvent-free Conditions

Diaryl ethers are frequently found in substructures of many biologically important natural products. Diaryl ethers can be commonly synthesized via two general ways which include Ullmann ether synthesis and aromatic nucleophilic substitution (SNAr) based addition reactions. In general, classical Ullmann diaryl ether synthesis required high boiling solvents, stoichiometric amount of organocuprate catalyst, and long reaction times. In recent years, diaryl ether synthesis based on SNAr addition reactions have received considerable attention. For example, various diaryl ethers have been synthesized from the method utilizing the reaction of phenols with electron deficient aryl halides in the presence of potassium fluoride-alumina and 18-crown-6. However, in this method the reactions usually required longer reaction times ranged from hours to several days in refluxing acetonitrile which limit its practical utlilization. Recently, microwave-assisted organic synthesis in various solvents as well as under solvent-free conditions have received tremendous investigation. By applying microwave irradiation to certain organic reactions, it is often possible to reduce reaction times from many hours to a few minutes. In addition, recent large demand for environmentally-friendly and less hazardous chemical reaction processes have stimulated the development of clean reactions that avoid use of excess amount of toxic and volatile organic reaction solvents. In particular, microwave-assisted reactions coupled with solvent-free conditions that involve the exposure of neat reactants to microwaves received great attention. This ecofriendlier technique has many practical advantages over conventional methods in terms of rapid reaction, operational simplicity, cleaner reaction, and increased yield. A couple of methods for the preparation of diaryl ethers using refluxing solvents under microwave irradiation conditions are recently reported. However, to the best of our knowledge, the only previous example for the microwaveassisted synthesis of diaryl ethers via SNAr based reaction under solvent-free conditions was reported briefly by the reaction of 4-fluoronitrobenzene with phenol in the presence of potassium hydroxide. As part of our ongoing program for the development of microwave-assisted organic reactions, we need to develop an efficient and facile synthetic method for diaryl ethers in solvent-free conditions using microwaves. Herein, we report our preliminary results on the microwave promoted synthesis of diaryl ethers under solvent-free phase transfer catalysis (PTC) conditions. Treatment of phenols with nitroaryl fluorides, KF-alumina and Aliquat 336 under microwave irradiation in a domestic microwave oven provided the corresponding diaryl ethers in high yields. When the reactions were conducted in the absence of the PTC catalyst, the negligible amounts of the diaryl ethers were detected. After careful screening of several phase transfer catalysts (TBAB, 18-crown-6, and

Solvent-free reactions as green chemistry procedures for the synthesis of cosmetic fatty esters

Solid–liquid solvent-free phase transfer catalysis (PTC) and acidic catalysis in dry media were applied, as green chemistry procedures, to the synthesis under mild conditions of long chain aliphatic esters of interest in the cosmetic field. The reactions were performed under conventional heating and microwave activation, analysing the profiles of the temperature increases during the reactions and studying the yields at different reaction times. The selected esters were obtained with very good yields within short reaction times.Using Aliquat 336 as phase transfer agent, the results showed lower yields under classical heating for very short reaction times (5 min), but usually comparable to the yields obtained under microwave heating extending the reaction time up to 15 min.The simple heterogeneous mixture of reagents with catalytic amount of neat p-toluenesulfonic acid (PTSA) under classical heating leads to good results, similar to those obtained under microwave activation with regards to yields and reaction times (10 min for microwave activation/15 min for oil bath).

Microwave activation and solvent-free phase transfer catalysis for the synthesis of new benzylidene cineole derivatives as potential UV sunscreens

Microwave activation coupled with solvent-free phase transfer catalysis (PTC), as a green chemistry procedure, was applied to the synthesis of new benzylidene cineole derivatives as potential UVA filters. Considerable improvements over classical procedures are put into evidence when using KOH + K2CO3 as the base and TBAB as the phase transfer agent. Comparison with conventional heating in strictly the same conditions as under microwave revealed an important specific non-thermal microwave effect. Preliminary studies to evaluate the photochemical behaviour of these new derivatives were carried out.

Solvent-free phase transfer catalysis under microwaves in fullerene chemistry. A convenient preparation of N-alkylpyrrolidino[60]fullerenes

A facile synthesis of a series of N-alkylpyrrolidino[60]fullerenes by phase transfer catalysis without solvent under microwave irradiation is described.

Structural determination by NMR spectroscopy and molecular mechanics of the regio and diastereoisomers obtained in the addition of 2-phenylcyclohexanone to chalcone

The structure and stereochemistry of the six regio and stereoisomers obtained in the reaction of 2-Phenylcyclohexanone 1 with chalcone 2 by solvent-free phase transfer catalysis has been determined by a combination of NMR techniques and molecular mechanics calculations. The validity of the method has been confirmed by the X-ray structure determination of isomer 7.

Synthesis of long chain aromatic esters in a solvent-free procedure under microwaves

Alkylation with n-octyl bromide of several substituted benzoic acids was performed under solvent-free phase transfer catalysis with excellent yields (≥ 95%) within very short times (2–7 min). Terephthalate octylation was raised from 20% to 92% under microwave activation when compared to conventional heating thanks to intrinsec effects of the radiation.

Improvements in Methylation of Diospyrol by Solvent-Free Phase Transfer Catalysis

Abstract Permethylation of diospyrol was considerably improved in solvent-free PTC conditions. An excellent yield (92%) was obtained in 30 minutes using solid KOH + 5% Aliquat 336 and dimethyl sulfate, to be compared with 40% in acetone in 10 hours.

Coupling focused microwaves and solvent-free phase transfer catalysis: Application to the synthesis of new furanic diethers

A new family of furanic ethers was obtained by alkylation of 2,5-furandimethanol or furfuryl alcohol under microwave in phase transfer catalysis (PTC) conditions in the absence of solvent. Products were synthesized in good yields (> 80 %) within 10 min or less. Compounds were analysed by NMR, mass spectrometry and their thermal behaviours were studied by DSC. When compared to conventional heating, everything equal elsewhere, reaction times were improved under microwave conditions at a restitute power of 30 Watts when performed under stirring in a monomode reactor (Synthewave 402 Prolabo).

Selective Alkylations of 1,2,4-Triazole and Benzotriazole in the Absence of Solvent

Alkylation of 1,2,4-triazole and benzotriazole has been performed either in basic media under solvent free phase transfer catalysis conditions or in the absence of base by conventional and microwave heating. Several parameters affecting the selectivity have been studied. In the case of triazole alkylation, microwave irradiation produces specific (non thermal) effects both on reactivity and selectivity