Novel amides and Schiff's bases derived from 1,3,4-oxadiazole derivatives: synthesis and mesomorphic behaviour

The synthesis and liquid crystalline properties of novel achiral amides (Ia–g, IIa–g and IVa,b), achiral Schiff's bases (IIIa–g and Va–g), chiral amides (VI, VII) and chiral Schiff's bases (VIII–XI) incorporating a 1,3,4-oxadiazole ring are reported. All amides of the series I and II display an enantiotropic smectic A phase. The amide IVa,b did not show mesomorphic properties. Amides of the series Ia–g and IIa–g contain a flexible n-tetradecylthio chain, the other terminal substituent is an n-alkoxy chain and n-alkyl chain, respectively (n?=?4–10) and the 1,3,4-oxadiazole is in the terminal rigid core. Amides Ia–g have broader mesomorphic range and higher thermal stability than the corresponding amides IIa–g. Amides IVa,d contain the 1,3,4-oxadiazole ring in the centre of the rigid core and two flexible alkoxy chains as flexible terminal substituents. Thus, the mesomorphic properties are favoured if 1,3,4-oxadiazole is shifted to a terminal position of the rigid core. Schiff's bases IIIa–g display an enantiotropic dimorphism smectic C–smectic A. Schiff's bases IIIa–g have a broader mesomorphic range than the analogous amides Ia–g. Schiff's bases Va–g exhibit a dimorphism smectic A–nematic, and in contrast to this the analogous amide IVa,b did not show mesomorphism. The chiral amides VI and VII and chiral Schiff's bases X and XI did not show mesomorphic properties and only the chiral Schiff's bases VIII and IX display a chiral smectic C phase in a short mesomorphic range. A density functional theory theoretical study at the B3LYP/6–311++G(d,p) level was performed in order to analyse the structural features that must be related with the mesomorphic behaviour of the reported compounds.     

A catalytic system with high efficiency and recyclability based on Suzuki and Heck reaction in aqueous admicellar medium

A recyclable and non-phosphine solid palladium (II) catalyst was prepared and characterized by HR-MS , FT-IR , XPS , EDS , TGA , SEM , TEM and ICP . The Pd-catalyst exhibited high-performance catalytic activity in Suzuki and Heck C-C coupling reactions in an environmentally benign water medium. Further, the Pd-catalyst ( Z ₄ ) can be reused for 15 times with little decrease of activity through simple and efficient recovery. In addition, the turn-over number (TON) of Pd- catalyst can reach 380 at room temperature. These results proved that the Pd-catalyst has a stable structure and can be recycled many times, making the process sustainable.     

Synthesis,Crystal Structure,and Spectral Properties of a Cobalt(II) Complex with N‐Salicylidene‐p‐Toluidine

The complex Co(C₁₄H₁₃NO)₂Cl₂ with the protonated N‐salicylidene‐p‐toluidine ligand was synthesized from an ethanolic solution of CoCl₂·6H₂O and N‐salicylidene‐p‐toluidine. The crystal structure was determined from X‐ray single crystal data (monoclinic, space group Cc, a = 1496.2(3) pm, b = 1257.4(4) pm, c = 1544.6(3) pm, β = 115.01(1)°, Z = 4). Co²⁺ adopts a distorted tetrahedral geometry. The UV‐Vis and IR spectra of the complex are discussed.     

一种四氢苯并吡喃及其衍生物的水相合成

制备了一种以三乙烯二胺(DABCO)为基础的离子液体;在水溶剂中,以该离子液体为催化剂催化三组分一锅法制备四氢苯并吡喃的反应,得到2-氨基-3-氰基-4-芳基-7,7-二甲基-5-氧代-4H-5,6,7,8-四氢苯并[b]吡喃;考察了反应时间、催化剂用量、催化剂加入时间、反应温度对反应收率的影响,确定了最优反应条件;由不同的芳香醛和活性亚甲基化合物制备了一系列四氢苯并吡喃衍生物,并讨论了可能的反应机理.结果表明,所选用的合成反应条件温和、时间短、收率高、后处理简单,且催化剂重复使用4次催化效果变化不大;就反应机理而言,所用催化剂具有双重催化活性.     

Nanoparticles decorated with a Schiff's base for the microextraction of Cd,Pb, Ni,and Co in environmental samples

In this paper, we report a new liquid–liquid microextraction procedure called “nanoparticles decorated with a Schiff's base for the microextraction of Cd, Pb, Ni, and Co in environmental samples”. The developed procedure was utilized for the extraction of Cd, Pb, Ni, and Co in environmental samples. The Schiff's base was formed by reacting salicylaldehyde with 3‐aminopropyltriethoxysilane‐functionalized iron oxide nanoparticles. Analyte extraction was conducted in a capillary column system loaded with modified nanoparticles and triton X‐114 as dispersion medium. 1‐Butyl‐3‐methylimidazolium hexafluorophosphate was employed as an extraction solvent. Acidified methanol in ultrasonic bath was used as desorption solvent, and elemental determination was carried out with flame atomic absorption spectrometer. Characterization of modified nanoparticles was performed with FTIR spectroscopy and transmission electron microscopy. Solution pH, nanoparticles amount, dispersant concentration, ionic liquid, and temperature were optimized for the extraction. Detection limits obtained for Cd, Pb, Ni, and Co were 0.183, 0.201, 0.241, and 0.192 μg L^?1, respectively, and enhancement factors were 79.1, 86.4, 95.7, and 82.0, respectively. The reproducibility of the developed procedure was in the range of 3.98–5.10%. Validation was checked by applying the developed procedure on certified reference water samples. The microextraction based on nanoparticles decorated with Schiff's base was successfully applied for the extraction of Cd, Pb, Ni, and Co in real environmental water samples.     

Synthesis and antioxidant activities of Schiff bases and their complexes: a review

Schiff bases, named after Hugo Schiff , are aldehyde‐ or ketone‐like compounds in which the carbonyl group is replaced by imine or azomethine group. They are widely used for industrial purposes and also have a broad range of applications as antioxidants. An overview of antioxidant applications of Schiff bases and their complexes is discussed in this review. A brief history of the synthesis and reactivity of Schiff bases and their complexes is presented. Factors of antioxidants are illustrated and discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Eco‐friendly,ultrasound‐assisted,and facile synthesis of one‐pot multicomponent reaction of acridine‐1,8(2H,5H)‐diones in an aqueous solvent

A one‐pot, multistep synthesis of acridine‐1,8(2H,5H)‐diones ( 4a–m ) was achieved by three‐component reaction of dimedone ( 1 ) with an aromatic aldehyde ( 2a–m ) and an ammonium acetate ( 3 ) using water as a green solvent without any catalyst and a simple, easily handled, and ultrasonic technique as well as conventional method.     

Clean Synthesis in Water：Darzens Condensation Reaction of Aromatic Aldehydes with Phenacyl Chloride

The Darzens condensation reaction of aromatic aldehydes with phenacyl chloride proceeded very efficiently in a water suspension medium in the presence of triethylbenzylammonium chloride and only trans-2,3-epoxy-1,3-diaryl-1-propanones were formed which can be isolated simply by filtration.The structures of these compounds were confirmed by elemental analysis,IR and ^1H NMR spectra.Therir configurations are in agreement with that of the same compounds reported in the literature.Compared to the classical Darzens condensation,this new method has the advantages of good yields,high stereoselectivity,low running cost inexpensive and environmentally benign procedure.     

Electrochemical synthesis of polyhydroxylated aromatic derivatives substituted with mono- and dipyrimidinyl thioethers in aqueous medium

Polyhydroxylated aromatic pyrimidinyl thioethers are important compounds due to their potential anti-HIV integrase activity. The present work describes an electrochemical synthetic strategy and environmentally benign approach for the synthesis of these compounds, superior to conventional chemical reactions. Thus, the electrochemical oxidation of 4-substituted catechols and caffeic acid, in the presence of 2-mercaptopyrimidine derivatives 2, generates monopyrimidinylthio-substituted polyhydroxylated aromatics 3a–f in moderate yields. In the case of catechol itself and 3-substituted catechols, both mono- (3g–l) and dipyrimidinylthio-substituted derivatives (4g–l) were produced. Apparently, the anodic oxidation of catechol derivatives leads to nucleophilic addition products of types 3 and 4, which are different from the traditional nucleophilic substitution reaction of aryl halides and thiols. The electrochemically induced reaction mechanism is also discussed.     

Synthesis,Characterization, and Thermogravimetric Studies of a Phosphorus-Containing Dendron Built from 1,5-Diaminonaphthalene at the Core

A facile divergent synthesis of a phosphorus-containing dendron containing 1,5-diaminonaphthalene is described. The phosphorus-containing dendron, functionalized with a 1,5-diaminonaphthalene unit at the core and phenolic OH groups grafted at the periphery, has been accomplished in a versatile, simple fashion, using Schiff's condensation and nucleophilic substitution reactions with POCl₃, 3-hydroxy-benzaldehyde, 4-hydroxy-benzaldehyde, and 3-amino-phenol iteratively. The structures of intermediate dendrons were characterized by infrared, NMR (¹H, ¹³C, and ³¹P), liquid chromatography–mass spectrometry, and C, H, N analysis. The structure of the final dendron (6) was confirmed by infrared, NMR (¹H, ¹³C, and ³¹P), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and C, H, N analysis. The thermal stability and degradation of the resulting final dendron was checked by thermal gravitometric analysis/differential thermal analysis.     

Greener approach for synthesis of monodispersed palladium nanoparticles using aqueous extract of green tea and their catalytic activity for the Suzuki–Miyaura coupling reaction and the reduction of nitroarenes

A facile and green route for the synthesis of palladium nanoparticles (NPs) was developed utilizing non‐toxic and renewable natural green tea extract as the reducing, stabilizing and capping agent. The as‐prepared Pd‐NPs@G.Tea extract was characterized using UV–visible spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The Pd‐NPs@G.Tea extract could be used as an efficient and heterogeneous catalyst for Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo, bromo and chloro moieties, and also for the reduction of nitroarenes using sodium borohydride in an environmentally friendly medium. Excellent yields of products were obtained with a wide range of substrates and the catalyst was recycled multiple times without any significant loss of its catalytic activity.     

Development of a new catalytic and sustainable methodology for the synthesis of benzodiazepine triazole scaffold using magnetically separable CuFe2O4@MIL-101(Cr) nano-catalyst in aqueous medium

Magnetically retrieval CuFe₂O₄@MIL-101(Cr) metal–organic framework was successfully prepared from easily available starting materials and characterized using various spectroscopic and analytical techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy, elemental mapping, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, vibrating sample magnetometer, and inductively coupled plasma optical emission spectroscopy. The catalyst was then used in the synthesis of benzodiazepines containing a triazole moiety in water. The advantages of this protocol include high yields, reusability of the catalyst, and gram-scale synthesis.     

Zn(ANA)2Cl2 complex as efficient catalyst for the synthesis of dihydropyrano[2,3-c]pyrazoles in aqueous medium via one-pot multicomponent reaction: a green approach

Abstract

The first example of recyclable Zn(ANA)₂Cl₂ catalyzed tandem one-pot three-component protocol reaction between aromatic aldehydes, malononitrile, and phenylmethylpyrazolone to furnish 4-substituted-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (4a–l) in a short reaction time (～10?min) in aqueous media at room temperature is described.     

Synthesis of pyridine bases: general methods and recent advances in gas phase synthesis over ZSM-5 zeolite

Pyridine bases are widely used in pharmaceuticals, insecticides, and herbicides due to their high bioactivity. In this paper, in addition to the conventional synthesis methods for pyridine bases, recent advances in the gas phase synthesis of pyridine bases over the shape selective catalysts (ZSM-5) are described.     

Synthesis of polymers in aqueous solutions: Esterification reaction of poly(methacrylic acid) with alkyl halides using DBU in aqueous solutions

A convenient esterification reaction of poly(methacrylic acid) (PMAA) with certain alkyl halides was performed using 1,8-diazabicyclo-[5.4.0]-7-undecene (DBU) as a base in aqueous solution or in water. The esterification reaction of PMAA with propargyl bromide (PB) proceeded very smoothly and quantitatively at 30°C to give corresponding poly(propargyl methacrylate), although the rate of the reaction decreased with increasing water. The reaction of PMAA with benzyl bromide, o-nitrobenzyl bromide, and p-nitrobenzyl bromide gave corresponding poly(methacrylic ester) using DBU under suitable reaction conditions in water. The esterification reactions of PMAA with PB were carried out using certain organic bases such as triethylamine, 4(N,N-dimethylamino)pyridine and pyridine. Inorganic bases such as sodium carbonate, sodium hydroxide, potassium carbonate, and potassium hydroxide were also tried under the same conditions as with DBU. However, the degrees of estrification with all these bases was much lower than that with DBU. © 1996 John Wiley & Sons, Inc.     

Biginelli reaction in aqueous medium: a greener and sustainable approach to substituted 3,4-dihydropyrimidin-2(1H)-ones

An environmentally benign aqueous Biginelli protocol for the synthesis of substituted 3,4-dihydropyrimidin-2(1H)-ones using polystyrenesulfonic acid (PSSA) as a catalyst has been achieved. These microwave-assisted reactions proceed efficiently in water in the absence of organic solvent, with simple filtration as the product isolation step.     

A green synthesis of a simple chemosensor that could instantly detect cyanide with high selectivity in aqueous solution

A novel and simple cyanide chemosensor 2-(naphthalen-1-ylmethylene)malononitrile(L) was designed and synthesized via a green chemistry method in water without using any catalyst.The chemosensor showed an excellent sensitivity and selectivity for CN in aqueous solution.The detection limit could be as low as 1.6×10~7 moI/L(0.16μmol/L),which is far lower than the WHO guideline of 1.9μmol/L cyanide for drink water.     

Catalyst-free regioselective synthesis of benzopyran-annulated thiopyrano[2,3-b]thiochromen-5-(4H)-one derivatives by domino-Knoevenagel-hetero-Diels-Alder reaction of terminal alkynes with 4-hydroxy dithiocoumarin in aqueous medium

The synthesis of novel pentacyclic benzopyran-annulated thiopyrano[2,3-b] thiochromen-5(4H)-ones has been described by domino-Knoevenagel-hetero-Diels-Alder reaction of 4-hydroxy dithiocoumarin and O-propargylated salicylaldehyde in aqueous medium and in the absence of any catalyst. The single step reaction is highly regioselective and provides polycyclic heterocycles in high yields.     

A simple and clean procedure for the synthesis of polyhydroacridine and quinoline derivatives: reaction of Schiff base with 1,3-dicarbonyl compounds in aqueous medium

A clean and simple synthesis of benzo[c]acridine, benzo[a]acridine, pyrido[2,3-c]acridine and benzo[f]quinoline derivatives was accomplished in good to excellent yields via the reaction of Schiff base with 1,3-dicarbonyl compounds in aqueous medium catalyzed by TEBA. The structures were characterized by ¹H NMR, IR and elemental analysis, and confirmed by X-ray diffraction study.     

Synthesis of polymers in aqueous solutions: Polyaddition of bis(oxazolines) with dithiol in aqueous solutions

Polyaddition of bis(4-mercaptophenyl) sulfide ( BMPS ) with m-phenylenebis(2-oxazoline) ( MPBO ) proceeded very smoothly in the mixtures of aprotic ploar solvents such as N-methyl-2-pyrrolidone ( NMP ) with water to produce the corresponding poly(amide–sulfide) with high molecular weights at 90°C under nitrogen. The reaction of BMPS with MPBO , p-phenylenebis(2-oxazoline), and 1,4-butylenebis(2-oxazoline) was also examined in water under the same conditions, and it was found that the reaction proceeds successfully to give the corresponding poly(amide–sulfide)s with high molecular weights. These results mean that water along as well as the mixed solvents of aprotic polar solvents such as NMP with water can be uses as suitable reaction media for the polyaddition of bis(oxazolines) with dithiol to synthesize poly(amide—sulfide)s with high molecular weights. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2711–2717, 1997