Salicylaldehyde Derivatives Research Articles

Schiff Base polymers: synthesis and characterization

The reaction between a carbonyl group (aldehyde or ketone) with amine in suitable condition, the Schiff base compounds with an amine group with the general structure R1R2C=NR3 (R3 ≠ H) was prepared [1, 2]. These compounds were first prepared by German scientist Hugo Schiff. The Schiff base compounds are widely used as a ligand in the coordination chemistry [3, 4]. The division of these compounds is diverse and depending on the various parameters, they are divided into symmetric, asymmetrical, anionic, neutral types and etc. But in most cases the division of these compounds is based on the number of atoms that are coordinated to the center ion. Accordingly, they are divided into mono-, bi- and multi-dentate ligands. Important groups of these compounds are chelated bi-and tetra-dentate ligands, which can be obtained from the reaction of salicylic aldehyde and amine derivatives [5, 6]. The simplicity of providing, having different colors, stabilizing metal complexes and diverse applications has led many research groups to work on these compounds [1, 2, 5, 6]. The most important properties of these compounds are anion sensor [6–8] and avoid steel corrosion [9, 10]. In recent years the innovation of novel Schiff base polymers as thermally stable polymers play a vital role in many areas, among that the most important factor of thermally stable polymers for different industry. Because of that, these advances are interested in improvement of heat and thermal stability and safety. Day to day in this globalization, thermal stable polymers requires a long shelf life, along with monitoring the safety and quality based upon international standards. In this chapter it inculcates, thermally stable polymers such as PA, PI and PES and its stability, long life, mechanical and thermal properties for different applications.

Coordination modes of salicylaldehyde derivatives in the ruthenium(II) nitrosyl and bis(2,2′-bipyridine) ruthenium(II) complexes

Treatment of [Ru(NO)Cl3(PPh3)2] with one equivalent of 3,5-dibromosalicylaldehyde in the presence of triethylamine gave the ruthenium(II) nitrosyl complex [Ru(NO)(κ2-C,O-salBr2)Cl(PPh3)2] (1). Interaction of [Ru(bpy)2Cl2]·2H2O with one equivalent of 5-chlorosalicylaldehyde in ethanol/N,N′-dimethylformamide afforded the bis(2,2′-bipyridine)ruthenium(II) complex [Ru(bpy)2(κ2-O,O-salCl)](PF6) (2). Complexes 1 and 2 were well characterized by infrared, proton nuclear magnetic resonance spectroscopies along with microanalyses and their molecular structures were determined by single-crystal X-ray diffraction.

Synthesis, characterization and antibacterial effect of diarylmethylamine-based imines

Firstly, starting from benzoic acid the diarylmethanone compound was synthesized. The diarylmethanone was converted to the corresponding oxime and then reduced to the diarylmethylamine compound. Four different imine compounds were obtained from the condensation of the diarylmethylamine compound with four different salicylaldehyde derivatives. Antimicrobial activities against Gram (+) and Gram (−) microorganisms (Staphylococcus aureus, Bacillus cereus as the Gram (+); Escherichia coli and Salmonella typhimurium as the Gram (−); and Candida albicans as the fungi) were investigated.

Modulation of imine chemistry with intramolecular hydrogen bonding: Effects from ortho-OH to NH

Salicylaldehyde derivatives and their imines are important building blocks in organic and supramolecular chemistry. In an effort to expand structural diversity in the current work we changed ortho-OH in salicylaldehyde to NH of amide/sulfonamide and investigated the effect of resulting intramolecular hydrogen bonds on imine dynamic covalent chemistry (DCC). A suite of ortho-aminobenzaldehydes were readily synthesized, and X-ray and NMR data validated the existence of NH⋯O intramolecular hydrogen bonds. The formation and exchange of imines were then studied in acetonitrile, and the acidity of OH/NH significantly influenced the thermodynamics and kinetics of imine reactions. Furthermore, the role of OH/NH⋯N hydrogen bonds on imines was elucidated by the shift of aldehyde exchange equilibrium. Finally, the formation of imines was achieved in aqueous solutions. The mechanistic insights could pave the way for future applications in assembly and labelling.

Synthesis, spectral and structural characterization and biological activity of Cu(II) complexes with 4-(diethylamino)salicylaldehyde and α-diimines

In this article, synthesis, spectral and X-ray structure characterization, antimicrobial activity and Brine shrimp test of two new Cu(II) complexes with a salicylaldehyde derivative have been reported. Complexes [Cu(L)(bipy)]BF4·0.5H2O and [Cu2(L)2(phen)2](BF4)2 were obtained in the reaction of Cu(BF4)2·6H2O, deprotonated 4-(diethylamino)−2-hydroxybenzaldehyde ligand (L) and α-diimine (2,2’-bipyridine or 1,10-phenanthroline). The complex with bipyridine is mononuclear, containing one L and one bipyridine ligand in a distorted square-planar cation with a BF4− anion and lattice water molecule, whereas the complex with phenanthroline is a dinuclear centrosymmetric dimeric cation, containing two L ligands along with two phenanthroline ligands and BF4− anions. The coordination geometry of each Cu(II) ion can be described as an elongated square pyramid. MS-ESI spectroscopy indicated that [Cu2(L)2(phen)2](BF4)2 is mononuclear in DMSO solution. In vitro antibacterial and antifungal activity was tested against four Gram-positive, four Gram-negative bacteria and three fungal strains. Complexes showed significantly stronger antibacterial activities than parent ligands. The mononuclear phenanthroline complex in solution showed very good antimicrobial activity, which is comparable to the activity of the standard antibiotic amikacin against all tested bacterial strains. The same complex has better antifungal activity than fluconazole, which was used as a standard. Results of the brine shrimp test indicate that both complexes have good toxicity against Artemia nauplii.

Hybridization of Triphenylamine and Salicylaldehyde: A Facile Strategy to Construct Aggregation‐Induced Emission Luminogens with Excited‐State Intramolecular Proton Transfer for Specific Lipid Droplets and Gram‐Positive Bacteria Imaging

AbstractAggregation‐induced emission luminogens (AIEgens) with excited‐state intramolecular proton transfer (ESIPT) process have attracted significant attention in bioimaging applications owing to their high solid‐state emission efficiencies and large Stokes shifts. Herein, a series of simple AIEgens with ESIPT process, referred to as triphenylamine salicylaldehyde (TS) derivatives, are designed and synthesized by a rational hybridization of triphenylamine and salicylaldehyde units as the intramolecular rotor and ESIPT generator, respectively. Owing to the AIE and ESIPT effects, TS derivatives exhibit intense emission and large Stokes shifts (>140 nm) in the aggregated state. By altering the substituents in the triphenylamine units, their solid‐state emission varies from 490 to 590 nm. Owing to their excellent biocompatibilities and suitable lipophilicities, the TS derivatives are able to specifically and rapidly (<5 min) stain the lipid droplets in the cells in a wash‐free manner and successfully image the lipid‐rich tissue in vivo. Moreover, owing to their suitable hydrophilicity, TS and methoxyl substituted TS (TS‐OMe) are shown to stain gram‐positive bacteria with high selectivity.

Copper(II) complexes of aroylhydrazones: Preparation and structural characterization

Structures of solid copper complexes with aroylhydrazones obtained from nicotinic acid hydrazide and salicylaldehyde derivatives differing in substituents on the benzene ring were analysed by means of infrared (IR) and Raman spectroscopy. Studied aromatic hydrazones acted as neutral, monoanionic or dianionic tridentate ligands, depending on the tautomer form adopted during the complexation process. Various additional substituents on the salicylaldehyde originated ring were not involved in metal coordination, thus carbonyl/enolic oxygen, azomethine nitrogen and oxygen of the phenolic hydroxyl group were proposed as the coordination sites for the copper(II) ion. In all applied synthesis conditions Cu(II) complexes were obtained in Cu(II)/hydrazone molar ratio of 1/1, except for a hydrazone with nitro group, which did not form a complex with Cu(II) regardless of the synthetic conditions. Vibrational spectra indicated that hydrazone having only ortho-hydroxyl group with respect to the double CN bond as well as a hydrazone with an additional OH group in para-position on the benzene ring, formed monomeric copper(II) complexes including water as a ligand, while hydrazones with meta-substituents (Cl, OCH3) formed binuclear copper complexes, in which two copper(II) ions bridge hydrazone molecules via phenolic oxygen atom. Thermal properties of prepared copper(II) complexes were investigated by means of thermogravimetric analysis.

Salicylaldehyde derivative of nano-chitosan as an efficient adsorbent for lead(II), copper(II), and cadmium(II) ions

In this study, a biodegradable natural polymer chitosan was modified with salicylaldehyde to prepare salicylaldehyde functionalized chitosan nanoparticles (N-Ch-Sal). The N-Ch-Sal was characterized by atomic force microscopy (AFM), scanning electron microscopy-energy-dispersive X-ray (SEM-EDX), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The salicylaldehyde functionalized chitosan nanoparticles (N-Ch-Sal) (~80 nm) were then used for the adsorption of three heavy metals viz., Cu(II), Cd(II) and Pb(II) ions. The above-mentioned techniques were also employed for evaluation of changes in N-Ch-Sal after metal adsorption. The parameters affecting the adsorption of metal ions including pH, contact time, amount of adsorbent, initial metal ion concentration and the effect of interfering ions, were studied thoroughly and optimized. The concentration of metal ions remaining in the aqueous system after adsorption experiments was analyzed by ICP-MS. At optimal conditions, sorption capacity of Pb(II) ion was found to be highest i.e., 123.67 followed by Cu(II) (84.60) and Cd(II) (63.71 mg/g). The adsorption process followed the pseudo-second-order kinetic model and fitted well with the Langmuir adsorption isotherm. The adsorption method was applied to a real tap water sample for the quantification and removal of Pb(II) ions. The concentration of Pb(II) ions in the tested sample was 4.88 ppb.

Chemo‐ and Diastereoselective Synthesis of Pyrazolo‐tetrahydropyridines via Multicomponent Sequential Aza‐Diels‐Alder Reactions in Water

AbstractIn this study, we report a novel and an efficient strategy for the synthesis of chemo‐ and diastereoselective synthesis of pyrazolo‐tetrahydropyridines via a one‐pot multi‐component intramolecular Aza‐Diels–Alder reactions (ADARs) from benzoylacetonitrile derivatives, phenylhydrazine, salicylaldehyde derivatives, and styrenesulfonyl or cinnamoyl chloride in H2O as a green solvent. This synthesis procedure was also designed to follow the group‐assisted purification (GAP) chemistry, which can avoid traditional purification such as recrystallization and chromatography methods.

Frontispiece: Domino Transformations of Ene/Yne Tethered Salicylaldehyde Derivatives: Pluripotent Platforms for the Construction of High sp3 Content and Privileged Architectures

Frontispiece: Domino Transformations of Ene/Yne Tethered Salicylaldehyde Derivatives: Pluripotent Platforms for the Construction of High sp³ Content and Privileged Architectures

Synthesis and structural analysis of diorganotin(IV) complexes from salicylaldehyde derivatives and 3-amino-2-napthol

Eighteen mononuclear diorganotin(IV) complexes derived from tridentate Schiff bases and R2SnO (IV) oxides (R = Me, n-Bu, Ph) were synthetized by multicomponent reactions in moderate yields. Complexes were characterized by common spectroscopic techniques such as FT-IR, UV–vis, mass spectrometry and NMR (1H, 13C and 119Sn) spectroscopy analysis. Nine complexes were characterized by single crystal X-ray diffraction analysis (1c, 1d, 1g, 1k, 1n, 1o, 1p, 1q and 1r). 119Sn NMR spectra showed signals at δ = 135–145, 175–185 and 319–323 ppm for Me, n-Bu and Ph derivatives respectively, indicating the pentacoordination of the tin atoms. In solid state, for compounds 1c, 1d, and 1g a distorted octahedral geometry for tin atoms was observed owing the presence of intermolecular Sn⋯O interactions, while for compounds 1k, 1n-1r, the pentacoordinate environment for tin atoms is observed. At supramolecular level the presence of OH⋯O, CH⋯O, CH⋯X (X = Cl, Br), CH⋯π and π⋯π interactions allow the formation of 1D and 2D polymeric chains.

Domino Transformations of Ene/Yne Tethered Salicylaldehyde Derivatives: Pluripotent Platforms for the Construction of High sp3 Content and Privileged Architectures.

Diversity-oriented synthesis (DOS) has become a powerful synthetic tool that facilitates the construction of nature-inspired and privileged chemical space, particularly for sp3 -rich non-flat scaffolds, which are needed for phenotypic screening campaigns. These diverse compound collections led to the discovery of novel chemotypes that can modulate the protein function in underrepresented biological space. In this context, starting material-driven DOS is one of the most important tools used to build diverse compound libraries with rich stereochemical and scaffold diversity. To this end, ene/yne tethered salicylaldehyde derivatives have emerged as a pluripotent chemical platform, the products of which led to the construction of a privileged chemical space with significant biological activities. In this review, various domino transformations employing o-alkene/alkyne tethered aryl aldehyde/ketone platforms are described and discussed, with emphasis on the period from 2011 to date.

Henry Reaction Revisited. Crucial Role of Water in an Asymmetric Henry Reaction Catalyzed by Chiral NNO-Type Copper(II) Complexes

Chiral copper(II) and cobalt(III) complexes (1-5 and 6, respectively) derived from Schiff bases of (S)-2-(aminomethyl)pyrrolidine and salicylaldehyde derivatives were employed in a mechanistic study of the Henry reaction-type condensation of nitromethane and o-nitrobenzaldehyde in CH2Cl2 (CD2Cl2), containing different amounts of water. The reaction kinetics was monitored by 1H and 13C NMR. The addition of water had a different influence on the activity of the two types of complexes, ranging from a crucial positive effect in the case of the copper(II) complex 2 to insignificant in the case of the stereochemically inert cobalt(III) complex 6. No experimental support was found by 1H NMR studies for the classical Lewis acid complexation of the carbonyl group of the aldehyde by the central copper(II) ion, and, moreover, density functional theory (DFT) calculations support the absence of such coordination. On the other hand, a very significant complexation was found for water, and it was supported by DFT calculations. In fact, we suggest that it is the Brønsted acidity of the water molecule coordinated to the metal ion that triggers the aldehyde activation. The rate-limiting step of the reaction was the removal of an α-proton from the nitromethane molecule, as supported by the observed kinetic isotope effect equaling 6.3 in the case of the copper complex 2. It was found by high-resolution mass spectrometry with electrospray ionization that the copper(II) complex 2 existed in CH2Cl2 in a dimeric form. The reaction had a second-order dependence on the catalyst concentration, which implicated two dimeric forms of the copper(II) complex 2 in the rate-limiting step. Furthermore, DFT calculations help to generate a plausible structure of the stereodetermining transition step of the condensation.

Efficient synthesis and anti-bovine viral diarrhea virus evaluation of 5-(aryldiazo)salicylaldehyde thiosemicarbazone derivatives

An efficient procedure for the synthesis of 5-(aryldiazo)salicylaldehyde thiosemicarbazone derivatives 1-25 was achieved via the condensation of 5-(aryldiazo)salicylaldehyde derivatives I–V with N-(4)-substituted thiosemicarbazide derivatives. Antiviral activity of the synthesized compounds was carried out. From the obtained results, it was noticed that compound 11 has a strong antiviral activity.

Direct Formylation of Fluorine-Containing Aromatics with Dichloromethyl Alkyl Ethers.

Formylations of fluorine-containing aromatic compounds with dichloromethyl alkyl ethers have been investigated. Dichloromethyl propyl ether and dichloromethyl butyl ether have been applied for the formylation of fluorine-containing anisoles to give the corresponding aldehydes in good yields. Application of these ethers is preferable to that of methyl ether, which is prepared from volatile methyl formate. Reaction of fluorine-containing phenols with these dichloromethyl alkyl ethers did not give salicylaldehyde derivatives, leading instead to corresponding aryl formates in high yields. A plausible mechanism is discussed.

A New Alternative Synthesis of Salicylaldazine via Microwave Irradiation Method

Two diazine Schiff base ligands, HLa and HLb, derived from thiocarbohydrazide and salicylaldehyde derivatives were synthesized using the microwave-assisted synthesis approach. The confirmation of both ligands was elucidated through physiochemical and spectroscopy techniques as well as single X-ray crystallography diffraction. The analyses showed that the ligands synthesized were formed as azine instead of thiocarbohydrazone based on the missing thione, C=S moiety, throughout FTIR and NMR spectrascopic data. This finding was further concluded by X-ray crystal analysis. The biological properties of these ligands were screened using the disc diffusion method. The result shows that HLb shows significant inhibition towards all of the bacteria tested.

Green Formation of Novel Pyridinyltriazole-Salicylidene Schiff Bases.

In this work, water was used as solvent for the eco-friendly synthesis of imines under microwave irradiation. In the first step of the study, 5-pyridinyl-3-amino-1,2,4-triazole hydrochlorides were synthesized in the reaction of amino guanidine hydrochloride with different pyridine carboxylic acids under acid catalysis. A green method for 5-pyridinyl-3-amino-1,2,4-triazoles was developed with the assistance of microwave synthesis. In the second step, the eco-friendly synthesis of imines was achieved by reacting 5- pyridinyl-2H-1,2,4-triazol-3-amine hydrochlorides with salicylic aldehyde derivatives to produce 2-(5- pyridinyl-2H-1,2,4-triazol-3-ylimino)methyl)phenol imines. Microwave experiments were done using a monomode Anton Paar Monowave 300 microwave reactor (2.45 GHz). Reaction temperatures were monitored by an IR sensor. Microwave experiments were carried out in sealed microwave process vials G10 with maximum reaction volume of 10 mL. When alternative methods were used, it was impossible to obtain good yields from ethanol. Nevertheless, the use of water was successful for this reaction. After 1-h microwave irritation, a yellow solid was obtained in 82% yield. In this work an eco-friendly protocol for the synthesis of Schiff bases from 5-(pyridin-2-, 3- or 4- yl)-3-amino-1,2,4-triazoles and substituted salicylic aldehydes in water under microwave irradiation was developed. Under the found conditions the high yields for the products were achieved at short reaction time and with an easy isolation procedure.

Supramolecular synthesis of coumarin derivatives catalyzed by a coordination-assembled cage in aqueous solution

A self-assembled Pd4L2 cage is employed as a water-soluble molecular flask for the synthesis of functionalized coumarins from a series of salicylaldehyde derivatives and cyanoacetates/malononitrile. The catalytic reaction features mild aqueous conditions and broad substrate scope. Crystal structures of the host-guest complexes for two substrates and one analogous intermediate have been obtained, shedding light on the supramolecular reaction mechanism. Michaelis-Menten kinetic studies were performed in one typical case, revealing that the rate of product formation has been enhanced by over 23-fold in contrast to the background reaction without cage. Moreover, the same reaction catalyzed by a smaller Pd6L4 cage gives a mixture of products and much lower yields, suggesting that fine-tuning on the size and symmetry of the cages’ cavity is crucial for their applications in supramolecular catalysis.

Synthesis, characterization and structural analysis of bis-schiff bases using 3,3′-methylendianiline and salicylaldehyde derivatives

Seven N,N′-bis(salicylidene)diamines of common formula (2-OH-(5X)C6H3CN)2-Z [Z = CH2(m-C6H4), X = H (1a), X = CH3 (1b), X = Cl (1c), X = Br (1d), X = NO2 (1e), X = OH (1f) and (2-OH-(3OH)C6H3CN)2-Z [Z = CH2(m-C6H4) (1g)] have been synthesized and characterized by IR, NMR and mass spectroscopy. Molecular structures of 1a-1d and 1g were elucidated by X-ray diffraction, the structures are stabilized by two intramolecular OH⋯N hydrogen bonds. Furthermore, intermolecular bonds as OH⋯O, CH⋯O, CH⋯N and CH···Hal stabilize the structures at supramolecular level. Compound 1g showed in one side and intramolecular OH⋯N hydrogen bond and, at the other side and NH⋯O hydrogen bond, showing the presence of enol and keto tautomers at the same molecule, which could be attractive to use in sensors and no-lineal optics. Besides, compounds 1a-1d showed weak intermolecular π-interactions.

Design, synthesis, and biological activity of Schiff bases bearing salicyl and 7-hydroxycoumarinyl moieties

18 (11 novel) Schiff bases, derivatives of salicylaldehyde, 2-hydroxyacetophenone, and 6-acetyl-, 8-acetyl-, and 8-formyl-7-hydroxy-4-methylcoumarin were synthesized and characterized by their spectral studies. 6-Acetyl-7-hydroxy-4-methylcoumarin was prepared by novel method under microwave assistance. These Schiff bases were evaluated for antibacterial activities against 12 bacterial and six fungi strains in vitro. N-(3,5-Dichloro-2-hydroxybenzylidene)-4-aminobenzenesulfonic acid sodium salt proved to be the most active against Staphylococcus aureus and MRSA strains (MIC 0.0194 µmol/cm3). The substitution pattern, two chlorine atoms in the salicylidene ring and the SO3Na group, is probably the most beneficial for the activity against Gram-(+) bacteria strains. All Schiff bases were evaluated for cancer efficacy against CFPAC-1 and HeLa cell cultures originating from human pancreas cancer or human cervical cancer. Schiff bases derived from salicylaldehyde are highly effective in pancreas and cervical cancer cells; however, they demonstrate also substantial toxicity towards NIH3T3 cells. Derivatives of coumarin contain three highly selective compounds: 7-hydroxy-8-[(4-methoxyphenylimino)methyl]-4-methyl-2H-chromen-2-one, N-[(7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene]-4-aminobenzenesulfonic acid sodium salt, and 7-hydroxy-8-[1-(4-hydroxyphenylimino)ethyl]-4-methyl-2H-chromen-2-one suggesting more promising potential of the second group of substances.Graphical abstract